The Institute of Pennsylvania Hospital and University of Pennsylvania School of Medicine
Historically, the phenomena of hypnosis that have aroused the greatest amount of popular and scientific interest are those that appear to transcend normal voluntary abilities. Attempts to experimentally validate claims of enhanced performance by hypnotized individuals not only have contributed conceptually to an understanding of hypnosis, but also have led to many important methodological developments (e.g., Barber, 1969; London &. Fuhrer, 1961; Orne, 1959; Sheehan & Perry, 1976). Certainly, too, the possible potentiation of human abilities by hypnosis holds considerable pragmatic and therapeutic promise; some of this promise has already been realized, as in the clinical use of hypnosis in the control of pain (J. R. Hilgard & LeBaron, 1984; Orne & Dinges, 1984).
Consistent with this enduring interest in the "extraordinary" potential of hypnosis, a great deal of attention has turned recently to its purported effectiveness in reviving memories that seem to elude normal waking efforts at recollection. Much of the evidence for this hypermnesic effect of hypnosis derives from data obtained in the clinical context -- highlighted by the early work of Breuer and Freud (1895/1955) in the treatment of hysteria. By the beginning of the 20th century, hypnotic hypermnesia was already being classified among the phenomena of hypnosis by major textbooks on the subject (e.g., Bramwell, 1903/1956; Janet, 1925; Moll, 1889/1958). Moreover, several pioneering laboratory experiments seemed to provide empirical evidence for these clinical impressions, documenting a tendency for enhanced recall of temporally remote memories in hypnosis as contrasted with ordinary waking recall (see Hull, 1933, pp. 111-127). Thus, the belief that hypnosis may aid in the recovery of lost memories is virtually contemporaneous with the disciplines of modern psychiatry and psychology.
22 Mechanisms of Memory Enhancement with Hypnosis
Nevertheless, the major impetus to the present resurgence of interest in this topic has been the enthusiastic response by many law enforcement agencies to proposals and demonstrations of the usefulness of hypnosis in the forensic context. Proponents of the use of hypnosis in police investigation point confidently to a number of cases (e.g., the Chowchilla, California, kidnapping, reported in Kroger & Doucé, 1979) in which decisive evidence was apparently uncovered following the hypnotic interviewing of a witness or victim of a crime.
However, the use of hypnosis in the forensic setting has not been limited solely to the purpose of developing leads to physical evidence. In some instances, defendants have voluntarily submitted to hypnotic memory enhancement procedures in an effort to recall information that might help to reduce charges against them or to exonerate them. In other situations, hypnotic memory "refreshment" has been employed where there is a paucity of objective evidence to corroborate the fragmented, inconsistent, or vague recollections of a witness or victim. There is currently considerable controversy over the extent to which the use of hypnosis in an attempt to facilitate testimony in court is justified, given its potential to create a miscarriage of justice.
In this chapter, we examine the current scientific status of the facilitation of memory by hypnotic techniques. Our task begins with a conceptualization of the nature and characteristics of hypnosis, emphasizing possible mechanisms that are relevant to memory enhancement. This is followed by a critical evaluation of the clinical and laboratory evidence delineating the conditions under which hypnotic hypermnesia may be manifested. We also seek to assess whether the risks of false recollections, vulnerability to memory distortion, and unjustified confidence can be exacerbated by hypnosis to the detriment of the legal process. Finally, we consider the impact of such factors in the clinical setting. The discussion focuses on the distinction between forensic and clinical goals and procedures, and their implications for the use of hypnosis in the context of memory retrieval.
HYPNOSIS: INTRINSIC FACTORS AND THEIR RELATION TO MEMORY ENHANCEMENT
The Nature of Hypnosis
One of the more salient aspects of hypnosis to an observer is an apparent increase in the subject's willingness to accept and to respond to suggestions given by the hypnotist. What distinguishes true hypnotic responding, however, is not simple behavioral compliance, but rather the person's ability to experience suggested alterations in perception, memory, or mood (Orne,
23 Reconstructing Memory through Hypnosis
1959, 1977). Whereas untrained nonhypnotized individuals can purposively feign the suggested distortions in a most convincing manner (Orne, 1959), the hypnotically responsive subject tends to experience the change as phenomenally real. These observations underscore the basic unreliability of overt behavioral compliance as a criterion of hypnosis. At the same time, they emphasize that the profound alterations in subjective experience (e.g., involuntariness, belief in the reality of the suggested event, etc.), which accompany attempts to respond to suggestions, constitute the essential characteristic of hypnosis.
A prerequisite for hypnosis is the willingness to adopt the role of "hypnotic subject," with its implicit social contract for uncritical acceptance of appropriate suggestions administered by the hypnotist (Orne, 1959; Sarbin, 1950; White, 1941). This requires the individual temporarily to relinquish reality orientation (Shor, 1959) and critical judgment and to allow the hypnotist to orchestrate the subject's experiences, with little concern for the inherent sense or nonsense of the suggestions or of his or her reactions to them.
The ability to experience hypnosis (i.e., hypnotizability) is a relatively enduring attribute of persons (Morgan, Johnson, & Hilgard, 1974), which has a near-normal distribution within the population (E. R. Hilgard, 1965). Consequently, all but a very few persons are capable of experiencing at least some of the effects of hypnosis when it is carried out in a facilitating context. Among the several factors that are important in this regard are the level of trust placed in the hypnotist by the subject; the subject's motivation to cooperate; and the kind of preconceptions the subject has concerning the nature of hypnosis and its effects. Thus, the induction of hypnosis actually begins with the hypnotist's efforts to establish rapport, while attempting to maximize the subject's expectations to respond and to allay any apprehension about the procedures to follow. Subsequently, any one of a variety of formal induction procedures can be used to promote the hypnotic condition.
General Effects of Hypnosis on Memory
Once an individual has been exposed to a hypnotic induction for the purpose of restoring memory concerning some earlier incident, a number of factors --including the expectancies and motivations of all parties involved, and the very context of hypnosis (apart from the nature of specific suggestions) -- may conspire to shape the content and/or quality of the memories that are reported. In view of the importance of this issue, particularly in the legal context, it seems useful to summarize these factors from the perspective of their implications for the validity and credibility of hypnotically accessed memories.
1. Hypnosis usually takes place in a calm, relaxed atmosphere that invites the subject to relinquish normal reality-monitoring activities, as well
24 Mechanisms of Memory Enhancement with Hypnosis
as responsibility for behaviors manifested during hypnosis. Such a context may be particularly well suited for the elicitation of additional details or novel information in memory reports, much of which the subject may otherwise have been too uncertain about to have reported. Thus, it is possible that hypnosis may not enhance memory per se; instead, it may simply lower the threshold for reporting uncertain items of information.
2. Involvement in imagination or fantasy is an integral component of hypnosis (e.g., J. R. Hilgard, 1970), and one that is instrumental in producing many of the positive effects obtained with the technique in psychotherapeutic and medical applications. Indeed, hypnosis has been defined as "believed-in imaginings" (Sarbin & Coe, 1972). It is therefore reasonable to anticipate that fantasy productions may intrude upon and enmesh with historically valid portions of the memory reports of hypnotized persons.
3. Following the induction of hypnosis, individuals manifest an increase in suggestibility (Hull, 1933), in part as a direct consequence of their willingness to put aside critical evaluative functions while in hypnosis. As a result, memories accessed during hypnosis may be contaminated -- wittingly or unwittingly -- by the way in which suggestions are given, as well as by casual remarks or subtle cues of the hypnotist or others present during the session. Subsequently, it may be impossible for the subject to distinguish such "implanted" details from true memories.
4. When the subject has a belief about an incident in the past, but lacks full recollection of the events that occurred, hypnosis may serve as a catalyst to transform this belief into what is experienced as an actual memory. The increased tendency toward fantasy and the decrease in critical judgment, coupled with the conviction that hypnosis will produce accurate recall, may allow the subject to visualize what he or she believes might have happened and to accept the hypnotic visualization as a true memory of what actually occurred.
5. Without any special knowledge or training, individuals can successfully simulate being hypnotized, and it is exceedingly difficult to detect such purposive simulation (Orne, 1977).1 Moreover, subjects who are in fact deeply hypnotized are still able to lie. Thus, it would be possible for a subject to willfully distort recollections in hypnosis (or while feigning hypnosis), in an effort to enhance the appearance of cooperation or otherwise to serve his or her own interests (Orne, 1961; Orne, Dinges, & Orne, 1984b).
6. Separate from the matter of the veridicality of memories retrieved with hypnosis, there are also characteristics of hypnotic experience that more
25 Reconstructing Memory through Hypnosis
directly affect the credibility of the subject's memory reports. The subject's willingness to accept fantasy as reality during the hypnotic experience, together with the often dramatic vividness of recollections in hypnosis, may inspire great confidence that the recalled material is true to fact. In turn, the subject's conviction that these memories are accurate, and the greater number of details reported subsequent to hypnosis, confer credibility upon his or her memory reports in the minds of others, regardless of their factual status. These processes are often reinforced by the popular misconception that persons are unable to lie when hypnotized and/or by the widely held belief that hypnosis can produce increases in accurate memory (Orne, Soskis, Dinges, & Orne, 1984).
In conclusion, the hypnotic context provides a number of nonspecific influences that may underlie the apparent utility of hypnosis in restoring memory. However, we are particularly interested in assessing the nature and extent of effects that are specific to, or a direct consequence of, the hypnotic process. For example, posthypnotic amnesia is a hypnotic phenomenon in that it requires an appropriate suggestion administered to a hypnotizable person following the induction of hypnosis. Similarly, a demonstration that hypermnesia is specific to hypnosis would require that it result from appropriate suggestions given to a hypnotizable individual after induction. Another possibility is that an effect may be due to the trait of hypnotizability, independent of hypnotic induction. In subsequent sections of this chapter, we try to determine the extent to which the effects of hypnosis on the facilitation of memory can be demonstrated and which specific and nonspecific effects may contribute to the phenomenon.
POTENTIAL MECHANISMS OF HYPNOTIC MEMORY ENHANCEMENT
Our consideration of hypnosis and the role of the hypnotic context in promoting increased memory has focused thus far on processes extraneous to memory that nevertheless can have an important influence on the apparent recovery of forgotten information. In this section, we briefly examine several theoretically relevant cognitive processes purportedly involved in normal memory, which can be assumed to covary with or be made more accessible by hypnosis. Thus, one might reasonably inquire, "What aspects of normal memory are likely to be influenced by hypnosis?" Or, to phrase it another way, "Why should memory be affected by hypnosis at all?"
Our approach to such questions begins with the almost universal conceptualization of memory as a three-stage process involving the acquisition, retention, and later retrieval of information (e.g., Bourne, Dominowski, &
26 Mechanisms of Memory Enhancement with Hypnosis
Loftus, 1979; Gleitman, 1981). Moreover, in considering the processes by which hypnosis might facilitate recovery of memories, our discussion is confined to mechanisms of retrieval. It is likely, in any case, that deficits related to the acquisition or storage of information would prove unresponsive to attempts at memory remediation by hypnotic or any other means, since in such instances the memory "trace" either was never encoded or was physically ablated, as through organic disease or physical insult. Hypnosis may prove valuable, however, in cases involving retrieval failure, where certain cognitive mechanisms activated by hypnosis may reinforce normal retrieval functions or provide alternate access to the unrecovered memories. Here we consider several hypotheses that posit mechanisms of this sort in the effects of hypnosis on memory.
A purely intuitive basis for anticipating that hypnosis might make contact with mechanisms necessary for the enhancement of memory derives from the phenomenon of suggested posthypnotic amnesia among individuals who have experienced deep hypnosis (L. M. Cooper, 1972; Kihlstrom & Evans, 1979). What is striking is the apparent ease with which such amnesia can be induced and subsequently lifted in hypnotically responsive subjects, simply by administering the relevant suggestion. The reversible nature of posthypnotic amnesia provides assurance that the target memories have not decayed but are merely temporarily inaccessible (Orne, 1966). More importantly, the potential of the amnesia suggestion to render specific memories inaccessible to recall, coupled with the ease of reinstating these recollections by simple suggestion, indicates a pliancy to hypnotic suggestion of some critical substrate of information recovery from the memory store. Thus, it is possible that a direct suggestion for hypermnesia may also activate this substrate in a manner analogous to the cancellation of posthypnotic amnesia, and thereby may breach nonsuggested spontaneous amnesia as well (Nace, Orne, & Hammer, 1974).
Another class of memory retrieval failures consists of those commonly precipitated by an experience involving severe psychological trauma. Amnesias of this nature involve motivated forgetting or repression -- that is, the active exclusion of unacceptable memories from conscious awareness. In extreme cases, however, the inaccessible memories have an etiological role in certain serious clinical disorders (e.g., hysteria, fugue states, and multiple personality). Interestingly, it was the striking similarity of certain hypnotic phenomena (e.g., limb catalepsy, sensory anesthesias, and spontaneous amnesia) to
27 Reconstructing Memory through Hypnosis
the symptomatology of hysteria -- noted in the experiments carried out by Charcot at the Salpêtrière and by Bernheim at Nancy -- that suggested a possible relationship between the two conditions to many 19th-century students of psychopathology (Janet, 1925; see also Ellenberger, 1970). Recent clinical evidence (Frankel, 1976; Spiegel & Spiegel, 1978) confirms that some of these dissociative disorders share characteristics common to hypnosis and are often associated with hypnotizability. Given this long-standing conceptual intimacy between naturally occurring dissociative states and their hypnotic analogues, the use of hypnosis in the treatment of psychogenic amnesia followed logically. Indeed, there are now numerous clinical case reports describing recoveries of repressed memories, and the abatement of corresponding psychological symptoms, following either spontaneous or suggested age regression in the context of hypnotherapy (e.g., Cedercreutz, 1972; Conn, 1960; Frankel, 1976; Garver, Fuselier, & Booth, 1981; MacHovec, 1981; Raginsky, 1969; Spiegel, Shor, & Fishman, 1945; Twerski & Naar, 1976).
Unfortunately, the absence of control procedures in such case studies leaves the mechanism(s) involved in the breaching of amnesia by age regression largely unilluminated. Perhaps the commonality between characteristics of hypnosis and dissociative symptoms is indicative of a common cognitive substrate providing access to ideas and emotions blocked from awareness. Alternatively, hypnosis, via age regression techniques, may be successful in restoring inaccessible memories by mentally reinstating conditions present at the time of the original incident, thereby increasing the availability of relevant retrieval cues. Finally, it is useful to consider the possibility that the memories that are "recovered" following hypnotic age regression may not be the same ones that were "lost"; that is, the hypnotically recovered memories may consist of an indeterminable ratio of fiction to fact. Nevertheless, this lack of historical accuracy need not diminish the therapeutic value of the recollections. The significance of this possibility is taken up in greater detail in a later section.
Mental imagery has been recognized as an important factor in human cognition and memory (e.g., Neisser, 1967; Paivio, 1969). The use of imagery during encoding is thought by many researchers (e.g., Paivio, 1969) to facilitate later recall of certain types of verbal information. For example, the recall of paired-associate nouns can be significantly improved when, during study, subjects imagine the referents of each such pair interacting in some way (Bower, 1970).
Imagery also appears to play a role in the representation of events in memory (e.g., Kosslyn, 1981; Paivio, 1971), as suggested, for example, by studies involving the mental rotation of objects (L. A. Cooper & Shepard,
28 Mechanisms of Memory Enhancement with Hypnosis
1973), image scanning (Kosslyn, 1973), and comparative judgments between images of objects (Paivio, 1975). Moreover, it has specific relevance for the storage of personal experiences in "episodic memory," where items are characterized solely by their perceptible properties and their temporal-spatial relations to other experienced events (Tulving, 1972). Finally, experimental data (e.g., Sheehan, 1972) indicate that imagery production may be a particularly useful strategy for the retrieval of incidentally acquired information -- the kind of information that is often of considerable importance in both the clinical and forensic contexts.
Whatever advantage hypnosis may confer upon the retrieval of episodic experiences from memory can reasonably be linked to its capacity to increase image utilization and vividness (K. S. Bowers, 1976; Crawford & Allen, 1983; S. Sanders, 1969; Sheehan, 1979). In this connection, there is considerable evidence indicating a positive relationship between hypnotizability and vividness of imagery (P. G. Bowers, 1978, 1982; Shor, Orne, & O'Connell, 1966; Spanos, Valois, Ham, & Ham, 1973; Sutcliffe, Perry, & Sheehan, 1970; 't Hoen, 1978) -- a finding that is consistent with the purported tendency for hypnosis to affect imagery. However, this relationship also suggests the possibility that in some circumstances where hypnosis appears to enhance the production of imagery, it does so in a permissive fashion, giving expression to a trait that is associated with the ability to experience hypnosis. In such cases, any corresponding memory enhancement, rather than implying a role for imagery-mediated retrieval, may conceivably reflect a bias in the manner by which events were originally encoded in memory (i.e., "holistic" vs. "detail-oriented" or "deep" vs. "superficial" processing), which is correlated with the individual's imagery ability.
It is well established that encoding strategies that favor deep processing (Craik & Lockhart, 1972) result subsequently in better recall and recognition performance. Moreover, there is some evidence (Crawford & Allen, 1983) that hypnotically responsive subjects are more likely to employ deep-level (imagistic or holistic) processing of visual stimuli, particularly during hypnosis, with the result that performance on tasks dependent upon visual memory is significantly facilitated. Thus, there is support for the view that imagery-mediated retrieval mechanisms evoked during hypnosis, or possibly information-processing biases associated with imagery ability and hypnotic responsiveness, may play some role in the effects of hypnosis on memory.
Reinstatement of Encoding Context and Mood
One way in which hypnotic age regression procedures may interact with imagery processes aroused during hypnosis to facilitate memory is by elaborating images of the context in which the forgotten information was origi-
29 Reconstructing Memory through Hypnosis
nally encoded. Mentally reconstructing the contextual cues present during encoding may then permit those same cues to guide the process of retrieval, much as an experimenter's explicitly providing an appropriate retrieval cue at test reliably enhances a subject's recall relative to an uncued test (Tulving & Pearlstone, 1966).
Compelling evidence for the effectiveness of mentally reinstating the context at acquisition was provided by S. M. Smith (1979), who showed that memory for verbal material was enhanced by recalling the material in the same room in which it was learned. Furthermore, he demonstrated that even when recall was attempted in a different room, memory could be improved simply by visualizing the original learning environment. A related finding was reported by Malpass and Devine (1981), using a "guided-memory" procedure with witnesses to a staged vandalism that had occurred 5 months earlier. Essentially, this technique consists of a series of specific questions that provide considerable correct information and then ask the subject for additional related details. Subjects were instructed to visualize aspects of the original environmental setting, including others present and their activities, as well as to remember whatever thoughts, feelings and reactions they might have experienced at the time of the critical events. Following the detailed guided-memory interview, witnesses were more accurate in identifying the vandal in a photographic lineup than were witnesses who were simply asked to identify the vandal's photograph. Similar findings with eyewitnesses have been reported using a "cognitive interview" technique that also relies upon context reinstatement, as well as repeated attempts to mentally review the events from different perspectives and in different temporal orders (Geiselman et al., 1984).
Cognitive retrieval strategies of this nature, if part of the hypnotic procedure, may account for memory improvement (e.g., Shaul, 1978; Stager & Lundy, 1985). However, such results may not invariably be obtained (see Loftus, Manber, & Keating, 1983; Sturm, 1982), due, among other factors, to situational variability in the degree to which contextual cues become associated with the critical events during encoding or in the degree to which they can be reinstated at recall.
The "context" associated with an event may also include effects that the situation produces on the affective experience of an observer. Research indicates, moreover, that a person's mood or level of autonomic arousal while experiencing a particular event may determine the subsequent accessibility of memory for that event; accessibility is generally improved when the mood state during retrieval is similar to the mood state at acquisition (M. S. Clark, Milberg, & Ross, 1983; Teasdale & Fogarty, 1979). The capacity to alter an individual's mood by hypnotic suggestion (Hodge, Wagner, & Schreiner, 1966; Orne & Hammer, 1974) appears to provide a potentially effective
30 Mechanisms of Memory Enhancement with Hypnosis
technique for the recovery of mood-specific memories, as demonstrated by the research of Bower and his associates (Bower, 1981; Bower, Monteiro, & Gilligan, 1978).2 Thus, hypnotic reinstatement of the affect uniquely associated with certain episodic events may possibly increase the availability of relevant retrieval cues, and consequently may improve an individual's memory for such events.
Multiple Retrieval Attempts and Nonhypnotic Hypermnesia
An alternative process to those considered above, which has nothing to do with hypnosis per se, may occur as the product of allocating extended time and effort to memory retrieval. Laboratory studies suggest that the amount of information retrieved from memory on any given recall trial is often not exhaustive of the total set of items available in storage (e.g., Brown, 1923; Tulving & Pearlstone, 1966). Moreover, particularly in circumstances where pictorial or imagistic stimuli have served as input material (Erdelyi & Becker, 1974; Erdelyi, Finkelstein, Herrell, Miller, & Thomas, 1976; Erdelyi & Kleinbard, 1978; Popkin & Small, 1979; Roediger & Payne, 1985), repeated memory testing has been found to yield progressive increases in accurate recall over trials. This effect (referred to as hypermnesia) appears to involve a true increase in memory accessibility as opposed to a change in report criterion3 (e.g., reporting an increasingly higher proportion of guesses over successive trials), since intertrial increments in correct recall occur even when subjects are required to produce a constant high output across trials (Erdelyi & Becker, 1974; Erdelyi & Kleinbard, 1978).
Some researchers (e.g., Roediger & Payne, 1982) have suggested that hypermnesia occurs specifically because of repeated testing (whether conducted at an overt or a covert level), which conceivably leads to better organization of recall and hence to more efficient retrieval strategies over trials. Regardless of the underlying mechanism, however, the phenomenon is robust and reliable under a variety of multitrial-recall conditions (Erdelyi, 1984;
3. When memory is indexed by the information a person is able to recall with or without the aid of retrieval cues, it seems to us useful to refer to the subjective standard that the individual invokes to distinguish information retrieved from memory as the "report criterion." In a recognition task, where the person is not required to produce information, but merely to judge (typically by responding "yes" or "no") whether some currently presented information is the same as that which was previously encoded in memory, we refer to the level of subjective certainty required for a "yes" response as the "response criterion."
31 Reconstructing Memory through Hypnosis
Roediger & Payne, 1985), given appropriate imagistic or meaningful stimulus materials.
The significance of this phenomenon for understanding the potential enhancement of memory by hypnosis resides in the simple fact that the efficacy of hypnosis is assessed in many situations by the uncovering of previously inaccessible memories. That is, one or more overt or covert attempts to retrieve the elusive memories in the normal waking condition precede the use of hypnosis to aid recollection. This pattern is probably characteristic of the majority of cases in which clinical hypermnesias with hypnosis have been observed, and is true of virtually every instance in which hypnosis has been used for investigative purposes by law enforcement officials. These same issues also apply to laboratory studies of hypnotic hypermnesia where a hypnotic recall follows a waking test.
Thus, what is taken as support for the efficacy of hypnosis in aiding memory retrieval may at times be a true hypermnesic process, but one that has little to do with hypnosis per se. Of course, the ubiquity of nonhypnotic hypermnesia resulting from repeated recall attempts does not preclude effects in hypnosis of the kinds of cognitive processes that we have discussed above. Indeed, nonhypnotic hypermnesia can be thought to subsume a variety of such effects, as suggested, for example, by its apparent dependence on imagery processes. However, the phenomenon of nonhypnotic hypermnesia requires that apparent memory enhancement effects attributed to hypnosis be evaluated against the proper baseline control procedure -- one that takes account of the role of repeated testing, retrieval time, and effort in facilitating recall.
This section has reviewed certain mechanisms of normal memory that conceivably may be optimized by the hypnotic process. Our objective in selecting representative mechanisms has been to highlight those that may readily (perhaps unwittingly) be brought into play, even in nondirective applications of hypnotic procedures. For example, it does not necessarily require a specific suggestion to alter mood; age regression to a psychologically disturbing episode in a person's life can be quite effective! Then, too, the list is not exhaustive, and other possible mechanisms could be appended, such as anxiety reduction (cf. Erdelyi,. 1985, pp. 240-242) or memorial "focusing" (Loftus, 1982).
Consequently, it should be clear that many of the procedures utilized during hypnosis incidentally involve the kind of cognitive strategies discussed above. Since these strategies can be shown to affect recall without hypnosis, it becomes relevant to ask whether hypnosis or hypnotizability adds to, or interacts with, these processes to yield hypermnesia. We turn our attention now to the rapidly accumulating scientific literature to evaluate the evidence bearing on this issue.
32 Mechanisms of Memory Enhancement with Hypnosis
EMPIRICAL STATUS OF THE FACILITATION OF MEMORY BY HYPNOSIS
Hypnotic Age Regression
Near the end of the 19th century, psychiatry had become alerted to the pathogenic influence of persistent memories (both conscious and unconscious) of early traumatic events as an etiological factor in many psychological disorders. Pierre Janet, in reviewing the clinical evidence for this prevalent viewpoint, outlined the rationale for the use of hypnosis in certain cases:
[I]t soon became apparent to me that many of the most important traumatic memories might be imperfectly known by the subject.... Sometimes we had to look for them when the patient was in a special mental condition; sometimes, lost memories would crop up in the somnambulist state, in automatic writing, in dreams. (1925, p. 594)
In an earlier work (L'Automatisme Psychologique, 1889, cited in Ellenberger, 1970), Janet described the hypnotic treatment of a patient, Marie, who during a previous hypnosis had attributed her present convulsive attacks and delirium to a childhood experience that occurred at the time of her menarche:
... I tried to take away from somnambulic consciousness this fixed and absurd idea that the menstruation was stopped by a cold bath. At first, I could not manage to do it; the fixed idea persisted . . . . I was able to succeed only thanks to a singular means. It was necessary to bring her back, through suggestion, to the age of thirteen, put her back into the initial circumstances of the delirium, convince her that the menstruation had lasted for three days and was not interrupted through any regrettable incident. Now, once this was done, the following menstruation came at the due point, and lasted for three days, without any pain, convulsion or delirium. (Ellenberger, 1970, p. 365)
This was one of the earliest reports of a psychotherapeutic use of hypnotic age regression, in this case for the purpose of hypnotically modifying the traumatic memories that subserved a hysterical illness; in other instances, Janet employed the technique to elicit the unconscious memories and emotions themselves, if they were not spontaneously forthcoming when the patient was questioned in hypnosis (cf. Ellenberger, 1970, p. 364). The issue of whether such hypnotically elicited memories had historical validity was not of relevance to Janet; his use of age regression involved supplanting whatever disturbing memories (veridical or not) the patient reported with psychologically more tolerable ones.
Freud's use of hypnosis was for a different purpose -- namely to explore the emotionally stressful childhood events that were thought to be the basis of patients' psychological symptoms (Breuer & Freud, 1895/1955). The phe-
33 Reconstructing Memory through Hypnosis
nomena that emerged in the course of this work endowed these hypnotic remembrances with an aura of credibility. Thus, the intense emotional reactions and the wealth of detail that characterized the hypnotic reminiscences of his patients, as well as the often dramatic alleviation of their symptoms subsequent to the hypnotic reliving of painful life events, originally had misled Freud to suppose that such recollections corresponded to true autobiographical occurrences.
But clinical experience soon caused Freud to question the historical accuracy of the recollections reported in hypnosis; he eventually came to recognize that while emotionally valid, these memories were not necessarily veridical relivings of traumatic childhood experiences (cf. Freud, 1906/1953, p. 274). Rather, the hypnotically elicited memories of such early events were often comprised of various proportions of fact, fantasy, and confabulation.
Laboratory research into the mechanisms of hypnotic age regression has typically concerned itself with whether age regression produces a genuine reviviscence -- an actual reliving of earlier developmental stages accompanied by behavioral, psychological, and physiological responses appropriate to such stages. Thus, several studies reported, with varying rates of success, the elicitation of the neonatal Babinski reflex to plantar stimulation when subjects were regressed to an age of 5 months or less (Gidro-Frank & Bowers Buch, 1948; McCranie, Crasilneck, & Teter, 1955; True & Stephenson, 1951). However, Barber (1962) reviewed evidence from three studies observing over 500 normal infants, and concluded that, contrary to popular belief, the Babinski sign was not the modal response to plantar stimulation among infants less than 7 months of age. Carefully controlled studies (e.g., McCranie et al., 1955) have also failed to document the claimed occurrence of spontaneous characteristic changes in electroencephalographic (EEG) patterns when adult subjects are age-regressed to infancy.
Similarly, a systematic replication and extension of the classic monograph study of Reiff and Scheerer (1959), carried out by O'Connell, Shor, and Orne (1970), revealed that many of the apparent developmental changes in cognitive functioning reported in the original investigation resulted from experimenter bias and situational demand characteristics. Of particular relevance to the present evaluation, however, was the failure of O'Connell et al. (1970) to find any evidence of hypermnesia during age regression for remote autobiographical information, such as the name of a subject's second-grade teacher or fellow classmates, as was apparently obtained in the original study of Reiff and Scheerer (1959). Other dramatic claims for hypermnesia during hypnotic age regression (e.g., True, 1949) also could not be replicated (Barber, 1961; O'Connell et al., 1970; Orne, 1951). In summary, the weight of experimental evidence from carefully controlled studies of hypnotic age regression fails to provide convincing support for a literal revivification process, at least in the domains of memory, physiological functions, and perceptual/ cognitive development.
34 Mechanisms of Memory Enhancement with Hypnosis
Some recent work (Nash, Johnson, & Tipton, 1979; Nash, Lynn, Stanley, Frauman, & Rhue, 1985) has demonstrated apparent age-dependent changes of an affective nature involving interpersonal and object relations (i.e., toward a transitional object), which occur in hypnotized, but not in simulating, subjects who are regressed to age 3. These findings suggest a possible link to mechanisms of the kind that occasion intense emotional abreaction when age regression is employed in the context of dynamic hypnotherapy. However, an interesting and highly germane footnote to the research program of Nash and his colleagues is that despite the more characteristically childlike affective response exhibited by hypnotizable subjects during age regression, the same subjects were significantly less accurate in recalling their own childhood transitional objects than were simulators, when retrospective reports by parents served as a criterion (Nash, Drake, Wiley, Khalsa, & Lynn, 1986). Of course, parental memory surely cannot constitute an infallible standard; hence this finding should be regarded merely as suggestive, but, as we shall see, it does not stand alone.
Hypnotic Effects on Recall and Recognition of Verifiable Facts
One common methodological weakness associated with research on hypnotic age regression, and illustrated in the aforementioned study by Nash et al. (1986), is the difficulty of obtaining reliable corroborative evidence with which to determine the veridicality of the subject's apparent memories (see also O'Connell et al., 1970; Reiff & Scheerer, 1959). The issue is not peculiar to the research laboratory; indeed, it is a crucial and persistent concern in the forensic use of hypnosis, and although the validity of memory may be of lesser importance to the psychotherapeutic process, its verification in the clinical setting is no less problematic. Consequently, when the evidence for hypnotic hypermnesia is being evaluated, those studies in which there is explicit foreknowledge of or control over the to-be-remembered stimuli must be weighted more heavily, because they are able to identify confabulations and pseudomemories. Due to space limitations, a critical review of each of these studies is not possible here. Instead, we focus discussion on certain key investigations and draw generalizations, where warranted, from other related experiments.
Meaningful versus Nonmeaningful Stimulus Material
With only a single exception (Augustynek, 1978, 1979), attempts to demonstrate memory enhancement by hypnosis have failed when the stimulus items have been devoid of either inherent or contextual meaning. Although the studies whose findings give rise to this conclusion vary considerably in
35 Reconstructing Memory through Hypnosis
methodological sophistication, they are nevertheless remarkably consistent on this score. Among the memory materials found to be intractable to hypnotic enhancement procedures are nonsense syllables (Baker, Haynes, & Patrick, 1983; Barber & Calverley, 1966; Dhanens & Lundy, 1975; Eysenck, 1941; Huse, 1930; Mitchell, 1932; White, Fox, & Harris, 1940); lists of unrelated words or word pairs (Das, 1961; Salzberg & DePiano, 1980; Young, 1925); and ostensibly irrelevant, incidental, or peripheral details (Baker et al., 1983; Young, 1926; but see DePiano & Salzberg, 1981, and Sheehan & Tilden, 1984, for exceptions involving meaningful peripheral materials).
On the other hand, the various stimulus materials that tend to be conducive to apparent memory enhancement by hypnosis are those that can be characterized as more or less personally, intrinsically, or contextually meaningful. Thus, pictures, poetry, stories, films, and other thematic materials have been found to give rise to greater recall during hypnosis than during the nonhypnotic condition (DePiano & Salzberg, 1981; Dhanens & Lundy, 1975; Rosenthal, 1944; Stager & Lundy, 1985; Stalnaker & Riddle, 1932; White et al., 1940). However, stimulus meaningfulness is not a sufficient condition to ensure the superiority of the hypnotic treatment over waking memory. Thus, the impact of the hypnotic intervention may be greater with subjects high, rather than low, in hypnotizability (Dhanens & Lundy, 1975; Dywan & Bowers, 1983; Stager & Lundy, 1985); or it may fail to differentiate hypnotic and nonhypnotic recall (McConkey & Nogrady, 1984; Nogrady, McConkey, & Perry, 1985; Putnam, 1979; Sheehan & Tilden, 1983), particularly when hypnosis is compared with motivating instructions (L. M. Cooper & London, 1973; Nogrady et al., 1985; Shaul, 1978).
The influence of stimulus meaningfulness on the expression of hypnotic hypermnesia may be attributable to differential constraints on the extent of spontaneous perceptual processing of meaningful and nonmeaningful materials (Shields & Knox, 1986). This conceptual outlook derives from the levels-of-processing framework of Craik and Lockhart (1972), which holds that retention is a positive function of the depth of analysis or extent of encoding elaboration an item receives. Accordingly, nonmeaningful materials, by definition, lack semantic attributes that are necessary for deep-level processing and hence are poorly registered and poorly retained in memory. In contrast, meaningful stimuli can (but need not) be more readily submitted to deep-level analysis (i.e., processed semantically and/or associated with existing cognitive structures) to ensure their persistence in memory and accessibility during retrieval. Support for the view that hypnosis may improve memory for deeply, but not shallowly, processed stimuli that have been equated for meaningfulness has been reported by Shields and Knox (1986; see also Crawford & Allen, 1983), but was not found in a face recognition task (Redston & Knox, 1983). Further experimental work is needed to determine whether this alternative conceptual approach provides better clari-
36 Mechanisms of Memory Enhancement with Hypnosis
fication of the conditions under which hypnotic memory enhancement may occur.
Recent versus Remote Memories
Laboratory studies of the effects of hypnosis on memory have generally confined themselves to assessing the retention of comparatively recently presented information. This bias has arisen and is maintained largely because of the difficulty in controlling variability of longer retention intervals, as well as other methodological considerations (e.g., the control of stimulus content and acquisition factors) and pragmatic issues (e.g., minimizing subject attrition). Unfortunately, such studies can be criticized from the perspective of their external validity for failing to adequately reconstruct the conditions around which real-life claims of the utility of hypnosis to improve memory often revolve. Thus, when hypnosis is employed in a police investigation or in a therapeutic setting, it is often for the purpose of helping individuals to remember the details of an autobiographical episode thought to have transpired days, weeks, months, or even years previously.
A good deal of the evidence relevant to this issue has already been taken up in the discussion of hypnotic age regression. On the basis of available data from properly controlled experiments and studies in which the researchers had access to biographical records, there is no support for the view that hypnotic age regression improves accurate recollection of childhood memories (cf. O'Connell et al., 1970).
In a classic investigation, Stalnaker and Riddle (1932) used subjects of high hypnotic responsivity to study the capacity of hypnosis to improve recall for poetry and prose selections learned at least 1 year previously. In terms of the total number of words from these selections that were correctly recalled by all subjects combined, hypnosis accounted for a gain of approximately 54% over ordinary waking recall. However, word counts and excerpts from some of the subjects' protocols obtained in both the waking and hypnotic conditions revealed the likely source of the superiority of hypnotic recall: As summarized by Stalnaker and Riddle, "the subjects wrote more of both correct and incorrect words in the trance state than in the waking" (p. 439). This indicates that the effect of hypnosis was primarily to increase the number of responses produced (correct as well as incorrect) over the number proferred during waking recall trials. In reviewing these findings in 1933, Hull already suggests the mechanism whereby the hypnotic enhancement effect might have been realized:
Moreover, there is strong indication in the Stalnaker-Riddle results that the standard of material which the subjects were willing to offer as satisfactory recall in the trance was considerably lower than that characteristic of the waking
37 Reconstructing Memory through Hypnosis
condition. It is conceivable that this difference in standard of certainty or accuracy may be entirely responsible for the increased amount of recall characteristic of the trance state. (p. 115)
These observations by Stalnaker and Riddle (1932) and by Hull (1933) directly pertain to what is now termed the "response criterion problem" (Klatzky & Erdelyi, 1985). Very simply, the "problem" is that an increase in correct recall does not distinguish whether hypnosis actually improves the accessibility of information in memory, or instead merely liberalizes the subject's criterion for reporting such information. The qualitative evidence highlighted by Stalnaker and Riddle and by Hull is, however, more consistent with the latter possibility.
The Stalnaker and Riddle (1932) study was also the first to focus on the increased tendency toward confabulation in hypnotic recollection. For example, one subject, who was unable in the waking condition to furnish the second stanza of Longfellow's "The Village Blacksmith," once hypnotized, "recalled" the following:
The smithy whistles at his forge
As he shapes the iron band;
The smith is very happy
As he owes not any man.
Considered on its own merits, the subject's reproduction appears quite plausible -- a common characteristic of confabulation. It possesses a realistic quality that results partly from the careful attention to structure (i.e., rhyme, meter) and style. But, with the exception of the final line, it bears only the faintest resemblance to Longfellow's original second stanza:
His hair is crisp, and black and long,
His face is like the tan:
His brow is wet with honest sweat,
He earns what e'er he can,
And looks the whole world in the face,
For he owes not any man.
Stalnaker and Riddle (1932) provide several other examples of the increased willingness of their subjects to confabulate or improvise verses of poetry while recalling in hypnosis -- an inclination that was relatively slight in the waking condition. It is not difficult to see how, in the absence of a source of verification, such confabulations can masquerade as true recollections, thereby appearing to confirm the effectiveness of hypnosis in restoring lost memories. The study by Stalnaker and Riddle, although interpreted by them to have clearly established hypnotic hypermnesia for meaningful material learned more than a year previously, remains, paradoxically, one of the most instructive sources of evidence available concerning pseudohypermnesic effects of hypnosis.
38 Mechanisms of Memory Enhancement with Hypnosis
More recent studies have investigated the effects of hypnosis on memories of approximately 1 week's vintage. Some of these have been concerned with the effects of hypnosis on eyewitness recognition memory for photographs of faces, videotaped crime sequences, and staged enactments. In all such cases, hypnosis failed to increase recognition accuracy beyond that of nonhypnotic performance (G.S. Sanders & Simmons, 1983; Wagstaff, 1982; Wagstaff, Traverse, & Milner, 1982), and actually led to fewer correct (G.S. Sanders & Simmons, 1983) as well as more incorrect identifications (Wagstaff, 1982; Wagstaff et al., 1982). L.M. Cooper and London (1973), using a within-subjects design involving immediate and delayed (2 weeks) cued-recall tests for meaningful information, found no significant improvement over waking recall due either to hypnosis or to hypnotizability. However, a significant nonspecific hypermnesia effect was obtained, in that all treatment groups exhibited greater recall on the second (delayed) test than they had on the first test.
A notable exception to the outcomes of the preceding studies is an experiment by Stager and Lundy (1985). These investigators found an increase in cued recall for information presented in a film 1 week earlier among hypnotizable subjects given a hypnotic treatment. What is striking about these results is that the increase in correct recall apparently occurred without a concomitant increase in errors -- a finding that would seem unlikely if hypnosis had merely augmented subjects' productivity. In view of the singular status of this pattern of findings and its implications for the hypnotic improvement of memory, two independent attempts (Lytle & Lundy, 1986; Whitehouse, Dinges, Orne, & Orne, 1987) to replicate these results were carried out, but neither could reproduce the hypnotic hypermnesia reported by Stager and Lundy (1985).
Impact of Emotionally Arousing Stimuli
The success of hypnosis in the therapeutic situation probably owes much to the fact that, whatever experiences are remembered during hypnosis, they often involve intense emotions of which the patient was previously unaware. Such "abreaction" is generally followed by clinical improvement. This covariation of memory and emotion leads naturally to debate over which process is responsible for the patient's improvement -- insight from the memory, or experience of the intense emotion, or both.
On other grounds, the relationship can be seen to exemplify notions of "encoding specificity" (Tulving & Thomson, 1973) or "mood-state dependency" (Bower, 1981), which have been proposed as determinants of the efficacy of memory retrieval processes. As we have seen, the work of Bower and his associates provides some indication that hypnosis can be utilized to modulate mood to provide greater access to memories characterized by
39 Reconstructing Memory through Hypnosis
similar affective tone (Bower, 1981; Bower et al., 1978). It should be noted, however, that failures to find mood-dependent retrieval with hypnosis have also been reported (e.g., Bower & Mayer, 1985), just as more generally applicable nonhypnotic procedures of mood induction (e.g., Velten, 1968) have successfully yielded mood-specific retrieval effects (Teasdale & Fogarty, 1979).
The characteristic of hypnosis that many consider instrumental to the uncovering of traumatic memories is its ability to diminish anxiety (e.g., Schafer & Rubio, 1978; Spiegel, 1980). Typically, hypnotic induction and deepening procedures are replete with suggestions for calmness, security, pleasantness, and profound relaxation. When accepted by the patient or eyewitness to a crime, these suggestions may coalesce to form a powerful antagonist to the fear and anxiety that otherwise may be aroused by remembering emotionally charged events, thereby making the individual more willing to think about and recall these events.4
Laboratory studies of the impact of hypnosis on memory for emotionally stressful events have yielded inconclusive results. An early investigation by Rosenthal (1944) found that hypnosis produced a significant increase (relative to nonhypnotic retrieval) in the recall of poetry and nonsense material that was learned in, and made relevant by, an experimentally induced anxious state. However, several more recent studies (Baker & Patrick, 1987; DePiano & Salzberg, 1981; Helwig, 1978; Shaul, 1978; Zelig & Beidleman, 1981) have failed to provide support for these findings. In view of the procedural differences among such a small number of studies, however, and the difficulties inherent in effectively controlling manipulations of stress and arousal, further experimental work is necessary before firm conclusions on the matter can be justified.
Forensic Simulation Studies and Case Illustrations
A number of researchers have assessed the effects of hypnotic procedures on memory for stimuli and events that share certain features with actual forensic cases. It is fair to say, however, that no laboratory studies successfully mimic, in all details, the circumstances confronting an eyewitness or victim of a crime (DePiano & Salzberg, 1981; M. C. Smith, 1983). Nevertheless, attempts to investigate these ecologically more relevant variables, albeit often in isolation, have yielded remarkably consistent observations.
In an investigation reported by Putnam (1979), subjects of equivalent
40 Mechanisms of Memory Enhancement with Hypnosis
hypnotizability viewed a videotape depicting a traffic accident. Subsequently, half of the subjects received a hypnotic induction while the remaining subjects did not, and all were questioned about details of the event while mentally reviewing the episode on an imaginary television set (cf. Reiser, 1976). Hypnosis did not increase the amount of correctly remembered information over the amount obtained in the nonhypnotic condition. However, 6 of the 15 questions that were put to all subjects were misleading questions, in that they were designed to subtly suggest a specific incorrect answer. Putnam found that hypnotized subjects were significantly more susceptible to making errors in response to these leading questions than were nonhypnotized control subjects. In addition, despite making more errors, hypnotized subjects were just as confident in the accuracy of their memories, both correct and incorrect, as were control subjects. A more recent study by Zelig and Beidleman (1981), using an emotionally upsetting accident film as a stimulus, obtained the same pattern of findings. Thus, hypnotized subjects made more errors in response to leading questions and exhibited misplaced confidence in the accuracy of their responses, compared with subjects tested in the waking condition. Again, though, hypnosis did not increase the quantity of accurate information beyond that provided by nonhypnotized subjects.
The failure of hypnosis to enhance memory under controlled conditions has been observed in several other investigations that have some generalizability to the forensic domain, such as studies involving films or slide sequences of vehicular accidents and criminal acts (Buckhout, Eugenio & Grosso, 1981; Helwig, 1978; G. S. Sanders & Simmons, 1983; Sheehan, Grigg, & McCann, 1984; Sheehan & Tilden, 1983, 1984; Sturm, 1982; Yuille & McEwan, 1985); studies involving staged incidents and mock crimes (Timm, 1981; Wagstaff et al., 1982); and most significantly, a major field study of hypnotic interviews by police officers of witnesses and victims of actual crimes (Sloane, 1981). Nearly as common is the finding that these hypnotically acquired memories are less reliable than nonhypnotic memories (G. S. Sanders & Simmons, 1983; Sheehan & Tilden, 1983; Sturm, 1982; Tallant, 1984; Wagstaff, 1982; Wagstaff et al., 1982), and incommensurate in accuracy with the degree of confidence that is placed in them (G. S. Sanders & Simmons, 1983; Sheehan et al., 1984; Sheehan & Tilden, 1983, 1984; Timm, 1982; Wagstaff, 1982; Wagstaff et al., 1982).
The aspects of hypnosis that make hypnotic recall less accurate and the subsequent memories less reliable are not mere laboratory curiosities, but have been demonstrated in a very considerable number of court cases in which hypnotically created testimony played a significant role (for an extended discussion of such cases, see Orne, Soskis, Dinges, Orne, & Tonry, 1985). Increased errors and confabulation in hypnotic recall were illustrated, for example, in People v. Kempinski (1980), where, during hypnosis, a witness "remembered" the facial characteristics of someone under conditions
41 Reconstructing Memory through Hypnosis
that vastly exceeded the limits of the human eye. Similarly, in State v. Mack (1980), a hypnotized person remembered eating a pizza in a restaurant that did not serve pizza, seeing tattoos on someone who had none, and having been stabbed with scissors or a knife where there was no evidence that a weapon was involved. The effect of leading questions was dramatically illustrated in State v. Forney (1984). In this case, a suspect was hypnotized and asked leading questions about a rake, which only the police, the hypnotist, and the assailant knew had been used on the murder victim. Subsequently, the suspects hypnotically created "recollection" of a rake was used as proof of his guilt, since the fact could only have been known by the true perpetrator. Finally, dangers associated with hypnotically augmented confidence are exemplified in numerous cases where a witness was originally uncertain about what had occurred, but subsequent to hypnosis became convinced, and in turn provided convincing testimony leading to an indictment and conviction of an individual (e.g., Commonwealth v. Kater, 1983; People v. Shirley, 1982; State v. McQueen, 1978).
Modification of Subjective Report Criteria
Regardless of whether a particular study shows an increase in correct recall or, alternatively, an escalation of inaccurate recall following a hypnotic induction, such evidence cannot tell us directly whether hypnosis has its effect on memory accessibility or upon the criterion that subjects adopt in reporting their remembrances. If hypnosis has a true effect on memory accessibility, it should act upon the same processes that are affected by variables such as the allocation of attention, stimulus familiarity and meaningfulness, rehearsal strategy, retention interval, and so on -- in short, mechanisms of information processing, storage, and retrieval. If, on the other hand, hypnosis modulates the threshold for acceptable recall, the effect may be brought about exclusively by performance factors, motivation, and incentives. Thus, for example, altering the consequences (i.e., payoffs and risks) for correct relative to incorrect memories can substantially change the amount of uncertain information an individual may be willing to report. Deciding between these alternatives requires special methodology, such as the application of signal detection theory (Green & Swets, 1966) to data obtained in the recognition memory paradigm, or the control of report criteria in free recall by requiring both hypnotized and nonhypnotized subjects to produce responses to the same (usually high) output level (Klatzky & Erdelyi, 1985). The critical evidence in all such studies relies on the concurrent evaluation of correctly recalled or recognized information (hits) and incorrect recalls (distortions, confabulations) and recognitions (false alarms). (For an expanded discussion of these issues and methodological procedures, see Erdelyi, Chapter 3, this volume.)
42 Mechanisms of Memory Enhancement with Hypnosis
Unfortunately, laboratory studies of the effects of hypnosis on recognition memory almost universally show no enhancement or a decrement compared with nonhypnotic recognition performance (e.g., Redston & Knox, 1983; G. S. Sanders & Simmons, 1983; Sheehan et al., 1984; Sheehan & Tilden, 1983; Timm, 1981; Wagstaff, 1982; Wagstaff et al., 1982). To our knowledge, the only contradiction to this general pattern was a study reported by Shields and Knox (1986), in which words studied at a semantic level of analysis were recognized more accurately by hypnotized subjects than by their nonhypnotized counterparts. This was a statistically significant but modest effect. On the whole, however, the amenability of recognition memory data to signal detection analyses for the purpose of separating potential hypnotic effects on memory from response bias or criterion effects appears to be quite beside the point; typically, there are no such effects of hypnosis to warrant analysis.
Very few studies have attempted the alternative strategy of controlling subjects' report criteria in the context of the free-recall paradigm. The first such study sought to evaluate the effects of hypnosis on memory for pictorial stimuli (Dywan & Bowers, 1983), using a modification of the forced-recall procedure developed by Erdelyi (Erdelyi & Becker, 1974; Erdelyi & Kleinbard, 1978). Using this technique, Dywan and Bowers repeatedly tested recall of a set of line drawings over a 1-week interval that culminated in a final forced-recall session in which half of the subjects were given a hypnotic induction procedure and half were given task-motivating instructions for enhanced recall. With potential differences in report criteria ostensibly controlled, both between treatments and within subjects, Dywan and Bowers (1983) found that highly hypnotizable subjects recalling in hypnosis retrieved significantly more additional correct items than did control subjects; however, they also produced three times as many errors!
Thus what appears to be a true memory-enhancing effect of hypnosis is dwarfed by the magnitude of recall intrusions elicited by the procedure. However, because the analysis was based only on novel correct and incorrect responses that the subjects confidently "presented as memories" (Dywan & Bowers, 1983, p. 184), the resulting data set was equivalent to one produced by a free-recall procedure (i.e., one dependent on report-criterion rather than that produced by the forced-recall method). Consequently, the data that were reported fail to identify the locus of the effect of hypnosis on recall. They are, nonetheless, fully consistent with the possibility that hypnosis merely liberalized the report criteria of the hypnotically responsive subjects.
This study is unique, however, in providing a quantitative estimate of the effects of hypnosis on recall following repeated concerted efforts to remember --conditions that virtually exhaust normal waking hypermnesia (e.g., Erdelyi & Kleinbard, 1978). This provides a conceptual parallel to the life situation of witnesses or victims who repeatedly try to remember what
43 Reconstructing Memory through Hypnosis
occurred in the course of a crime and are highly motivated to do so. Under such circumstances, hypnosis appears to allow the individual to tender previously unreported items as confident memories, even though most of them are incorrect. It is this aspect of hypnosis that makes it seem to an observer that the procedure brings forth totally new information, and thus makes it attractive as a technique to elicit inaccessible memories, particularly when they cannot be checked.
We have recently completed a study (Whitehouse et al., 1987) using the forced-recall methodology to assess the effects of hypnosis on interrogatory recall of filmed material. The focus of this study was to understand the nature of the hypnotic enhancement of correct recall reported by Stager and Lundy (1985). Although the positive effect observed in the Stager and Lundy study occurred without a concomitant increase in errors, the effect may nonetheless have been due to a shift in report criterion. This is possible because some of their subjects apparently availed themselves of a third response category -- effectively, "I don't know" -- or simply omitted responses to some questions (cf. Stager, 1974, p. 67). Thus, if hypnosis produced a shift in report criterion (i.e., an increased willingness to offer responses), then some of the "I don't know" responses given prior to hypnosis inevitably would be replaced by correct responses during the hypnotic recall, creating the appearance of enhanced memory. The fact that hypnotized subjects did not also produce more erroneous responses may have been due to the use of questions that provided an extensive amount of accurate description and detail to serve as retrieval cues for the target information.
To determine the viability of this interpretation, we employed the same materials and procedures that had been used by Stager and Lundy (1985), but in addition we required subjects to answer each question (by guessing if necessary), and to rate their confidence in the accuracy of each response. Two such forced-recall tests were carried out, the first of which occurred in the waking condition for all subjects. Half of the subjects were exposed next to a hypnotic induction and received suggestions for improved recollection, while the remaining subjects performed an irrelevant task, prior to being tested for recall a second time. Both groups of subjects recalled additional correct information on the second test, but the magnitude of improvement was no greater for hypnotized subjects than it was for waking subjects. Moreover, during this second recall, hypnotized subjects were more likely than were waking subjects to increase confidence ratings for responses previously identified as guesses, irrespective of their accuracy. This finding, that previously uncertain responses (which are not likely to be reported in the absence of a forced-recall requirement) were endowed with greater certainty in hypnosis, is consistent with the occurrence of a shift in report criterion.
A second forced-recall study by our laboratory (Dinges, Orne, Whitehouse, Orne, Powell, & Erdelyi, 1987) compared the efficacy of hypnosis to
44 Mechanisms of Memory Enhancement with Hypnosis
motivated waking recall using a multitrial hypermnesia paradigm (e.g., Erdelyi & Kleinbard, 1978). Subjects viewed a set of pictorial stimuli and, following a 1-week retention interval, they received a series of eight forced-recall trials. Although the complexity of the experimental design prohibits a detailed description, the important findings were: (1) All subjects (without regard to hypnotic versus waking treatment) continued to produce additional correct recall on each successive trial; (2) The recall improvement (i.e., hypermnesia) observed in hypnotized subjects was less than that seen in waking subjects; and (3) Although there was a significant general pattern among subjects to become more confident of their recall productions over trials, this effect was particularly evident in the confidence that highly hypnotizable subjects invested in their erroneous recall.
Each of these studies from our laboratory (Dinges et al., 1987; Whitehouse et al., 1987) relied on forced-recall procedures to prevent the occurrence of a shift in report criterion when hypnosis was induced. Neither found hypnosis to be superior to the waking treatment in eliciting further accurate recall; in fact, Dinges et al. (1987) observed a decremental influence of hypnosis on the hypermnesia normally observed with repeated attempts to remember. Although further research using this methodological approach is needed, these findings of no enhancement of recall by hypnosis when report criterion is controlled raise serious doubts about the reality of hypnotic hypermnesia.
Vulnerability to Memory Distortion by Postevent Information
Loftus and her colleagues (e.g., Loftus, 1979; Loftus, Miller, & Burns, 1978) have suggested that information encountered after a witnessed event has the potential to revise an individual's memory concerning specific details of the target event. Although this "integration" viewpoint has aroused theoretical controversy (Bekerian & Bowers, 1983; McCloskey & Zaragoza, 1985), the empirical phenomenon itself has been well established under conditions much like those of the typical eyewitness situation. Thus, when subjects are presented with subtle misinformation following a stimulus such as a slide sequence of a traffic accident, the incorrect postevent information can often be more readily elicited than the originally perceived details in subject's subsequent recognition memory reports.
In the context of hypnosis, where imagination, fantasy, and the uncritical acceptance of the hypnotist's suggestions are strongly encouraged and socially reinforced, there is a good possibility that the tendency to incorporate postevent information into memory may be exaggerated, particularly among highly hypnotizable persons. Studies germane to this topic have investigated the effects of two techniques known to induce memory distortion: the use of subtle leading questions (Loftus & Zanni, 1975), and the interpolation of misinformation between the target event and the memory
45 Reconstructing Memory through Hypnosis
test (Loftus, 1979). Following visual presentations depicting a traffic accident and a series of shop accidents, respectively, Putnam (1979) and Zelig and Beidleman (1981) exposed hypnotized and nonhypnotized subjects to leading questions such as "Did you see the stop sign at the intersection?" (Putnam, 1979) or "Did you see Lucky take off his hat after his friend died?" (Zelig & Beidlemen, 1981), which tended to suggest an affirmative response as being correct. Both studies found that subjects in the hypnosis groups responded significantly more often in the direction implied by the misleading questions, and therefore were more frequently incorrect, than nonhypnotized control subjects. These findings suggest that hypnosis served to sensitize the subjects to subtle cues that communicated the nature of the "memories" that were ostensibly being sought, rather than increasing the accessibility of the subjects' true memories. In fact, on nonleading questions, no difference in the accuracy of responses by hypnotized and nonhypnotized subjects (i.e., no hypnotic hypermnesia) was found in either of the two studies.
Using the paradigm of interpolated misinformation, recent studies conducted at Sheehan's laboratory (Sheehan & Tilden, 1983, 1984) have found no differential effect of hypnosis or of hypnotizability. That is, hypnotized subjects were neither more nor less likely than nonhypnotized subjects to incorporate earlier misleading information into their memory reports. These null effects for susceptibility to misleading postevent information contrast with findings (Sheehan & Tilden, 1984) of increased distortion in free narrative recall by hypnotically responsive subjects given hypnosis. Recently, however, Sheehan et al. (1984) introduced misleading information following a hypnotic-induction procedure, carried out with highly hypnotizable subjects, and with relatively unhypnotizable subjects instructed to simulate hypnosis, and obtained significantly greater integration of the suggested false information among the hypnotized group.
Thus, the results of Sheehan et al. (1984) are consistent with those of Putnam (1979) and Zelig and Beidleman (1981). These investigations indicate that vulnerability of memory reports to distortion by intentional or unwitting cues and by counterfactual information is particularly acute for hypnotically responsive individuals while they are in the hypnotic condition.
A recent demonstration by Laurence and Perry (1983) bears out and extends the implications of the preceding studies of memory distortion in hypnosis. Highly hypnotizable subjects were interviewed to establish that they had slept uneventfully through a particular night of the previous week. Following this, they were hypnotized and age-regressed to the night in question. During the hypnotic reliving of the night's sleep, the subjects were asked whether they had heard some loud noises that had awakened them. Out of 27 subjects, 17 responded to the suggestion implicit in the leading question and reported hearing noises that aroused them from their sleep. When hypnosis was terminated, some subjects were tested immediately, whereas the remaining subjects were tested 7 days later, for spontaneous (i.e.,
46 Mechanisms of Memory Enhancement with Hypnosis
nonsuggested) posthypnotic retention of the pseudomemory created in hypnosis. Overall, 13 subjects (6 with utter certainty) now recalled the noises and insisted that they had actually occurred and had awakened them during the night in question. Even when confronted with the fact that the noises had been suggested to them in hypnosis, they remained unshakeable in their conviction.
This demonstration by Laurence and Perry (1983) illustrates the malleability of memory in hypnosis; more importantly, it shows the persistence and seeming reality following hypnosis of such hypnotically created (distorted) memories. This point is crucial when the hypnotically "refreshed" memory of an eyewitness or victim forms the basis for courtroom testimony. Apart from the heightened susceptibility of hypnotized persons to sources of memory bias and distortion, their relative inability to distinguish between hypnotic memories (whether accurate or not) and prior waking recollections renders any such testimony incompetent (cf. Diamond, 1980).
Confidence, Accuracy, and Credibility
The demeanor of a witness, and particularly the level of confidence the witness conveys regarding his or her testimony, are major determinants of perceived credibility (Lindsay, Wells, & Rumpel, 1981; Wells, Lindsay, & Ferguson, 1979). At the same time, however, displayed confidence need have little to do with the accuracy of eyewitness information (Wells et al., 1979); many witnesses truly believe their incorrect memories.
It is a natural corollary to the "report-criterion shift" hypothesis of hypnotic hypermnesia that a consequence of the procedure will be an increase in confidence about one's memory productions (Orne, 1979). Those studies in which subjects' confidence in their reported memories was assessed between hypnotic and nonhypnotic treatments provide an overwhelmingly consistent confirmation of this view. Thus, for example, Dywan (1983) and Nogrady et al. (1985) -- both employing the multitrial-recall paradigm of waking hypermnesia (e.g., Erdelyi & Becker, 1974; Erdelyi & Kleinbard, 1978), with forced-recall and free-recall response formats, respectively -- found significant increases in both correct items over trials (i.e., productivity). This effect was greater for hypnotized subjects with high hypnotic ability in Dywan's study (see Dywan & Bowers, 1983), but was found not to differentiate groups in the Nogrady et al. study. Importantly, however, Dywan (1983) reported a corresponding increase in confidence due to hypnosis in highly hypnotizable subjects. Nogrady et al. (1985) similarly observed an increase in confidence for subjects high (but not for those low) in hypnotizability who were tested in the hypnotic condition -- an effect that was significantly associated with incorrect items during the last three recall tests. In both studies, therefore, the increase in confidence produced by hypnosis was attended by a parallel increase in intrusions, and hence was unjustified.
47 Reconstructing Memory through Hypnosis
Analogous findings have been reported in the memory distortion studies carried out by Sheehan and his colleagues (Sheehan & Tilden, 1983, 1984; Sheehan et al., 1984). Sheehan and Tilden (1983) found that highly responsive subjects displayed increased confidence in their recognition memory in the hypnosis condition, while hypnotizable subjects in the waking condition did not. Similarly, highly hypnotizable subjects asserted significantly greater confidence in memories elicited during hypnosis than they assigned to responses given on a subsequent waking test (Sheehan et al., 1984; see also Perry & Laurence, 1983). Sheehan and Tilden (1984) reported, however, that unhypnotizable subjects who were instructed to simulate hypnosis also exhibited increased confidence, even in regard to their distorted recognition responses. It appears, therefore, that the increase in confidence or certitude produced by hypnosis is consistent with subjects' preconceptions about the effects of hypnosis in retrieving accurate memories (e.g., Orne, Soskis, et al., 1984; Putnam, 1979).
In the domain of eyewitness identification, the confidence of a witness is often a key variable in determining whether a suspect can be charged and prosecuted successfully. Accordingly, many forensic simulation studies of hypnotic effects on memory have incorporated measures of confidence. Putnam (1979) and Zelig and Beidleman (1981) reported, not an increase in confidence during hypnosis, but rather a persistence of confidence despite an increase in errors due to leading questions. A similar pattern was obtained by G. S. Sanders and Simmons (1983): Both hypnosis and control subjects tended generally to be conservative in the degree of confidence they awarded to their recollections, but, for those items about which subjects were willing to testify in court, hypnosis subjects were significantly more often incorrect. In addition, in the Zelig and Beidleman (1981) study, a small but significant positive correlation (r = .33) was obtained between subjects' hypnotizability and their confidence ratings across treatment conditions, reflecting the tendency for highly hypnotizable subjects to place greater overall confidence in their remembrances. Finally, the use of hypnosis to enhance memory in lineup recognition tasks consistently fails to improve memory but often succeeds in escalating eyewitness confidence (G. S. Sanders & Simmons, 1983; Timm, 1982; Wagstaff, 1982; Wagstaff et al., 1982).
Another factor known to influence the credibility of a witness's testimony is the amount of peripheral detail he or she provides in recounting the events in question (see the analysis of John Dean's Watergate testimony in Neisser, 1982; see also Wells & Leippe, 1981). A shift in report criterion caused by hypnosis is one mechanism through which hypnotically accessed memories can differ from normal recollections in terms of a greater quantity of detail. Similarly, the inclination to confabulate and to draw inferences to fill in missing information is apparently greater in hypnosis, and, as a consequence, can render the memory reports of hypnotized individuals deceptively more believable than normal recall (e.g., Stalnaker & Riddle, 1932).
48 Mechanisms of Memory Enhancement with Hypnosis
In this regard, the studies of Sheehan et al. (1984) and Sheehan and Tilden (1984) showed that highly hypnotizable subjects who provided a free narrative recall during hypnosis introduced significantly more peripheral details -- both correct and incorrect -- and errors of inference than did unhypnotizable subjects simulating hypnosis. It is not clear, however, whether this was an effect of hypnosis or of hypnotizability, since the two variables were confounded in these experiments. An independent experiment by McConkey and Nogrady (1984) found a decrease in the number of correct inferences related to story recall; this was a function of hypnotic ability, but not of hypnosis. On the other hand, when subjects unselected for hypnotizability were exposed to either task-motivating instructions or hypnosis plus task-motivating instructions for hypermnesia of specifically cued peripheral details, there was a significant recall advantage for the hypnosis condition (DePiano & Salzberg, 1981). Thus, there is evidence that either hypnotic responsiveness or the effect of a hypnotic induction procedure, or both, serve to encourage the reporting of inferential and peripheral information. A consequence of this additional detail in the memory report is to endow such testimony with greater credibility.
SIGNIFICANCE OF EMPIRICAL FINDINGS FOR CONTINUED INVESTIGATION AND USE OF HYPNOSIS IN THE SERVICE OF MEMORY RECONSTRUCTION
Forensic Relevance in Research Designs
The continuing controversy over the utility of hypnosis for enhancing the memories of witnesses and victims of crimes (e.g., Diamond, 1980; Orne, Soskis, et al., 1984; Perry & Laurence, 1983; Reiser, 1985) has inspired vigorous research activity. Thus far, this research has begun to elucidate the promises, perils, and limitations of hypnosis in the legal context. However, there is a pressing need for properly designed studies that have high ecological validity, while possessing adequate methodological power to isolate the source of effects despite the limitations of the typical forensic setting.
There are numerous anecdotal reports (e.g., Block, 1976; Reiser, 1976) claiming to document increased recall as a consequence of hypnosis. Although in some of these cases it appears that hypnotically obtained information may have provided the clues essential to the apprehension of a suspect, it is generally impossible to determine the specific role, if any, that hypnosis played in eliciting this information. Some of the most widely cited statistics (e.g., Reiser & Nielson, 1980) are based upon ratings by the senior investigating officer about how useful hypnosis was, without providing any criteria on which these ratings were based; such data in consumer surveys are called "happiness reports."
49 Reconstructing Memory through Hypnosis
Any laboratory investigation that hopes to elucidate the processes underlying this phenomenon must involve a context in which at least apparent hypermnesia -- analogous to what is claimed in the field -- is produced. Such "apparent" hypermnesia need not consist of an increase in accurate memory; it might involve either more details or changes in what is remembered, or more overall novel information, in some combination or other. The failure to produce at least an ostensible hypermnesia may, like any null finding, help raise questions about the existence of hypermnesia, but it does not permit inference about other consequences of hypnosis (e.g., increased confidence) that might occur in situations where apparent hypermnesia is produced.
In addition, studies should attempt to distinguish whether the hypnotic treatment produces a bona fide increase in memory accessibility as opposed to a change in subjective report criterion. From a practical perspective, such a distinction might seem inconsequential. What difference should it make why novel memories become available in hypnosis, so long as they do? The answer is that hypnosis, as we have seen, has multiple effects (e.g., susceptibility to memory distortion, heightened confidence, etc.), many of which contraindicate its use in the legal context. Accordingly, analysis of the mechanisms of hypnotic memory enhancement will determine whether equally effective substitute procedures can be developed that do not entail the risks associated with hypnosis.
Efforts along these lines have already begun in the development of techniques such as "guided memory" (Malpass & Devine, 1981) and the "cognitive interview" (Geiselman et al., 1984); in fact, studies typically find no statistically significant differences in recall output between such procedures and hypnosis (Geiselman, Fisher, MacKinnon, & Holland, 1985; Sturm, 1982; Yuille & McEwan, 1985). Of course, it is important to consider that these retrieval mnemonics may be as efficacious as hypnosis in sponsoring increased memory productivity for the simple reason that they are not mere surrogates, but, like hypnosis, actively invite the subject to alter his or her standard of judgment. Furthermore, such techniques may explicitly tap some of the critical processes that inhere in hypnosis (see also E. R. Hilgard, 1984; Perry & Nogrady, 1985), including fantasy, imagery, and confabulation. It will be necessary for further research to decide whether these procedures provide viable alternatives to hypnosis or whether they share critical features of hypnosis, albeit in disguise.
Finally, research is needed on the role of perceived consequences as a motivational factor determining memory reports in the context of hypnosis. In reviewing the nonhypnotic literature on this topic, M. C. Smith (1983) concluded, "The results . . . do not support the hypothesis that processes underlying recall differ when there are perceived serious consequences associated with that recall" (p. 398). However, Orne (1961) suggested that the hypnotic context (independent of the condition of hypnosis) can serve as a facilitator of information that an individual may be fearful or embarrassed to report, or motivated by guilt to suppress. The function of the hypnotic
50 Mechanisms of Memory Enhancement with Hypnosis
context implicated here is the subject's abrogation of responsibility for information that is revealed in hypnosis, with the resulting perception of immunity from serious consequences. Thus, some of the differences in evidence for hypnotic hypermnesia that have been found between laboratory studies of hypnosis and its forensic use in the field may reside in the illusion of freedom from reprisal and/or legal sanctions that might ordinarily motivate witnesses to "forget" certain details of actual crimes. While this possibility has received some theoretical consideration (e.g., Perry & Nogrady, 1985; Timm, 1982), systematic research on the topic has yet to be inaugurated.
Contraindications for Courtroom Testimony
Elsewhere, we have reviewed evidence pertinent to the use of hypnosis for investigative purposes and in the preparation of a witness's testimony for trial (including the consequential hazards to justice), as well as the history of judicial posture on the admissibility of hypnotically "refreshed" testimony in court (Orne, Dinges, & Orne, 1984a; Orne, Soskis, et al., 1984; Orne et al., 1985). In the present chapter, we have cited evidence from a number of scientific studies that establishes (1) the fundamental unreliability of recollections elicited in hypnosis; (2) the persistence of these recollections in the waking condition, whereupon they may be impossible for the individual to distinguish from memories that existed prior to hypnosis; and (3) the unwarranted increase or maintenance of confidence in the accuracy of hypnotically elicited recall, which thereby reinforces its credibility. These considerations compel the conclusion that hypnotically induced memories should never be permitted to form the basis for testimony by witnesses or victims in a court of law.
To the degree that hypnosis may prove useful in searching for leads,5 risks are likely to be reduced in those investigative circumstances in which neither the person to be hypnotized, the authorities, the general public, nor the media have any substantive or presumptive knowledge or beliefs about facts relating to possible perpetrators. In the absence of any such preconceptions that could influence the nature of the memories reported, hypnosis remains an unreliable procedure, but it is less dangerous in the sense that it does not lead an individual to confirm his or her own beliefs or the suspicions of the hypnotist. It should be clear, however, that in such cases the purpose of the hypnotic intervention is to develop leads that result in new independent physical evidence, not to elicit testimony. Accordingly, the possible increases in inaccurate information that may attend any accurate recollections reported in hypnosis have the principal disadvantage of wasting time and effort, but if
51 Reconstructing Memory through Hypnosis
the investigative hypnotic session is carried out properly (see Orne, 1979; Orne, Soskis, et al., 1984), and it is recognized that the individual cannot subsequently testify, it need not threaten the interests of justice.
Recently, the Council on Scientific Affairs of the American Medical Association (1985) has issued a report on hypnosis and memory based on a comprehensive review of the extant scientific literature.6 It concludes as follows:
[H]ypnosis can be useful during the investigative process, when even a single correct recall may lead to important new evidence and where it matters relatively little if the hypnotized subject also produces many incorrect responses. This use of hypnosis is in stark contrast to its use with a witness who is to testify in court. . . .The value of [the] investigative use of hypnosis must be balanced against the potential testimonial incapacitation or restriction of evidence by the hypnotic subject as a trial witness. (1985, p. 1922)
The Council's report recognizes that hypnosis may be of some benefit in an investigative context, although it emphasizes the lack of scientific evidence to document a memory-enhancing effect of hypnosis, and it recommends procedural safeguards to protect the integrity of the memory report as well as the welfare of the subject and the public. Furthermore, the Council warns of the potential dangers to the judicial process of the use of hypnosis with witnesses whose testimony will be used in court. The position outlined in the Council's report echoes the concerns enumerated in twin resolutions previously adopted by the Society for Clinical and Experimental Hypnosis (1979) and by the International Society of Hypnosis (1979). Accordingly, there is now consensus among major groups within the relevant scientific community regarding the unreliability of hypnosis as a memory-restoring technique, and the potentially grave legal implications associated with its use in the forensic context.7
Relevance to Psychotherapy
In juxtaposition to the discouraging laboratory evidence for the hypnotic enhancement of memory are the clinical claims of dramatic memory recover-
6. This report is of particular interest because the official recognition of hypnosis as a therapeutic modality by the American Medical Association, and subsequently by the American Psychiatric Association and the American Psychological Association, has been taken as evidence in forensic areas for the acceptance of hypnosis to "refresh" recall, which has therefore justified its use as a basis for testimony in court. However, although the relevant scientific community considers hypnosis appropriate for therapy, it has never accepted the technique to be a reliable method of enhancing recall -- an issue that is clarified by the Council's (1985) report.
7. The American Medical Association's position (which was ratified by its House of Delegates in December 1984) was also adopted as the official position of the Society for Clinical and Experimental Hypnosis in 1985 and of the International Society of Hypnosis in 1986.
52 Mechanisms of Memory Enhancement with Hypnosis
ies brought about through hypnosis. We now consider some of the reasons that may account for this discrepancy.
The autobiographical memories retrieved with the aid of hypnosis in the clinical setting often deal with intense, meaningful experiences, some of which may be inaccessible to consciousness and involve material that is unacceptable to the individual. Laboratory studies of the efficacy of hypnosis in aiding recall of emotionally charged materials have thus far yielded equivocal results. However, it must be kept in mind that the laboratory rarely if ever reproduces the intensity of emotion associated with some autobiographical memories, and certainly does not approximate the guilt-related, highly personal, traumatic experiences that are often involved in treatment. Unless the stimulus material concerns experiential memories unacceptable to the individual and dynamically kept out of awareness, the relative ease of nonhypnotic recall would mitigate against positive findings.
Another possibility, acknowledged by Freud (1906/1953), that may have even greater generality and relevance is that the recollections of patients in hypnosis often include some measure of fantasy and confabulation that is not identified as such. As we have discussed above, the concomitants and sequelae of hypnotic recollections -- particularly the reporting of vivid details, the intense affect, and the therapeutic improvement resulting from abreaction -- tend to be accepted as convincing evidence that the patient's recollections are accurate. Moreover, the therapist is interested in the meaning, rather than the historical accuracy, of the abreacted experiences or other memories related during hypnosis. In age regression, for example, the therapist is not apt to challenge the veridicality of what is reported (except in a case of obvious anachronisms), since to do so, especially prematurely, may undermine treatment. For these reasons, together with the assumption that the patient would not jeopardize clinical improvement by deliberately inventing fictitious memories, the therapist's role involves accepting the patient's statements as historically accurate. Thus, the operational criteria for the validity of a "memory" in the context of psychotherapy are orthogonal to those of the laboratory and the forensic setting.
Reconstruction in Hypnotic Memory Retrieval
As we have seen, the task of the therapist is not to establish the accuracy of historical events recounted by the patient, but to help the patient to work through his or her own version of history, which may involve valid memories mixed with condensation, confabulation, and fantasy. At times, the therapeutic strategy of choice has been one that facilitates the "reconstruction" of that history. The early work of Janet (1889, cited in Ellenberger, 1970), and more recently the work of Erickson (1935; Erickson & Rossi, 1980) and others (e.g., Lamb, 1985), explicitly reveal the considerable therapeutic benefit that
53 Reconstructing Memory through Hypnosis
accrues from such constructions when ego-syntonic endings can be grafted onto memories of earlier traumatic experiences.
Many therapists feel that suggesting an ego-syntonic ending to earlier traumatic experiences is manipulative and therefore an inappropriate strategy. It is reasonable to assume, however, that when hypnosis is used in an attempt to reinstate traumatic memories, historical reconstruction takes place "spontaneously." One of the major advantages to the use of hypnosis as an adjunct to dynamic psychotherapy may be precisely the ease with which patients can alter their memories in response to subtle or unwitting cues. Given the diminution of the patient's critical faculties while hypnotized that allows him or her to accept the re-experienced events as memories, and given the features of hypnosis that render it convincing to the observer, hypnosis allows a reconstruction of history in ways that may be compelling to both therapist and patient. In this way, the therapist becomes able to provide validation for the importance and the presumed accuracy of the patient's memory. To be sure, such processes need not be dependent on hypnosis for their occurrence (see Spence, 1982), but they would seem to be facilitated by it. Thus, in the absence of hypnosis, some patients in psychotherapy may require more time and effort to work through the feelings associated with their memories in ways that make them acceptable.
In contrast to its utility in the reconstruction of "memory" in psychotherapy, the use of hypnosis in law enforcement is concerned with ascertaining the truth of the matter. Obviously, hard physical evidence is most desirable, but often it is simply not available. Eyewitness reports have a particularly vital status in the criminal justice system, but, unfortunately, these too are often not to be had. It is hardly surprising, therefore, that many law enforcement officials look to any potential scientific aid to make their difficult task more manageable. Just as the use of Amytal Sodium or Pentothal as a "truth serum" was once favored in law enforcement, so there is a tendency to accept a "new" investigative tool, such as hypnosis without adequate scientific data. A real danger is inherent in the willingness of investigators and prosecutors to accept the view that, because hypnosis yields additional details about which witnesses often tend to be certain after hypnosis, these novel recollections are likely to be accurate. The wish to believe in the accuracy of reports obtained during hypnosis is so strong that, in one case, a rape victim who had never seen her assailant because he wore a mask was instructed in hypnosis to remove the mask and look at his face! This "eyewitness" identification was actually used in an attempt to gain a conviction.
Obviously, in a forensic context, the accuracy of information is paramount; nevertheless, it may be impossible to ascertain what really happened in any specific instance. Despite the problems associated with recall induced by hypnosis, there is a temptation to argue that if the information obtained in hypnosis independently corroborates (or is corroborated by) other evidence,
54 Mechanisms of Memory Enhancement with Hypnosis
then the previously hypnotized witness should be permitted to testify. Unfortunately, this argument is seriously flawed, in that it is a simple matter to inadvertently create such corroborating "memories" in hypnosis. For example, the identification of a suspect may be corroborated by hypnotic recall created either by subtle cues that may be present during, or prior to (Alexander, 1971), the hypnotic interview, or by the translation of pre-existing beliefs into "recollections" via hypnosis. The "corroboration" thus obtained by the use of hypnosis is illusory. It is for such reasons that the overwhelming majority of courts that have ruled upon the matter have excluded testimony based on recollections of a witness following hypnosis, although some courts have permitted prehypnotic statements, reliably recorded, to be offered in testimony.
With regard to the clinical setting, however, the ability of hypnosis to alter memories in a psychotherapeutically desirable fashion may be useful. Clearly, the fact that a patient improves does not speak to the accuracy of the memories that were obtained, since purposively created pseudomemories can be therapeutic. Nonetheless, in hypnotic age regression, it often appears as if there is an actual reliving of an early childhood event, with accompanying accurate recollections. But in a clinical context, it is no easier than in a forensic one to ascertain the origin of the memory for such events. Thus, for example, it is not uncommon for a 2-year-old child to do something that is considered cute or precocious by the family, and hence the deed becomes worthy of periodic mention at family gatherings thereafter. If, as an adult, the individual "relives" the particular event while in hypnosis, and the facts are corroborated by a parent, this would not permit one to distinguish whether the recollection truly dates from age 2 or is the consequence of later family recountings. In a therapeutic context, such a distinction is unimportant; in qualifying an eyewitness in the forensic context, however, the source of the memory is the crucial issue.
We have sought to review the relevant scientific literature concerning the accuracy and consequences of memory elicited during hypnosis, and to discuss the implications of such evidence for the use of hypnosis in reconstructing memory in therapeutic and forensic settings. In the clinical context, the therapist and patient jointly define the events, realities, and "memories" that are relevant to the goals of psychotherapy, which involve helping the patient to cope more effectively and to feel better. The historical accuracy of remembered events is less important in determining the patient's therapeutic progress than is the manner in which the events are expressed, understood, and dealt with. On the other hand, in the forensic domain, an overriding
55 Reconstructing Memory through Hypnosis
commitment is made to the uncovering of "truth." Here, however, such truth cannot be determined by consensus of the witness and hypnotist.
Despite the well-known vagaries of normal human memory (Loftus, 1979), it is nevertheless considerably more reliable than are memories induced by the hypnotic process. It appears that the criminal justice system's traditional use of a jury as the trier of fact, of the adversarial process, and of cross-examination has served as the best available means of defining "truth." However, this process can be subverted by a technique, such as hypnosis, that greatly facilitates the reconstruction of history, that allows an individual to be influenced unwittingly, and that may catalyze beliefs into "memories." The resultant testimony may then be presented under oath by an honest individual who is convinced of the accuracy of what may well be pseudomemories. Paradoxically, then, the same attributes of hypnosis that make it a useful adjunct to psychotherapy also create the greatest obstacles to its use in the forensic domain.
At the present stage of scientific knowledge, we cannot distinguish between veridical recall and pseudomemories elicited during hypnosis without prior knowledge or truly independent proof. Perhaps future research will provide ways for making this crucial distinction. Until such techniques become available, testimony based on hypnosis or on any other procedures that invite fantasy, diminish critical judgment, and increase the risk of pseudomemories, should be prohibited.
Preparation of this chapter was supported in part by Grant No. MH 19156 from the National Institute of Mental Health, U.S. Public Health Service; in part by Grant No. 82-IJ-CX-0007 from the National Institute of Justice, U.S. Department of Justice; and in part by a grant from the Institute for Experimental Psychiatry Research Foundation. We are grateful to our colleagues Matthew H. Erdelyi,. Germain Lavoie, Campbell Perry, Helen M. Pettinati, and David A. Soskis for their valuable comments. We also thank Mary Fleming Auxier for editorial assistance.
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