The Perception of Temporal Order:
Fundamental Issues and a General Model.

Dedicated to the Memory of Robert R. Bush.

How do people judge the order of two nearly simultaneous stimuli, such as a light and a tone? We consider this question in the context of a general independent-channels model that incorporates most existing models of order perception as special cases, and which has been implicitly assumed when temporal-order judgments are used to study perceptual latency. In the model, a "decision function" converts a difference in central "arrival times" of two sensory signals into an order judgment. The psychometric function for order is regarded as a distribution function, and can be represented additively in terms of the central arrival latencies and the decision function. Various distinct decision functions correspond to various previously proposed mechanisms involving a "perceptual moment," attention switching, a threshold for arrival-time differences, and so forth (Section II).

One test of the model is to compare reaction-time measurements with order judgments (Section III). Discrepancies can be understood by an analysis of the concept of perceptual latency that recognizes the internal response to a pulse as being spread out in time (Section IV).

An alternative test is to determine whether experimental factors that influence two signal chnannels selectively have additive effects on the mean, variance, and higher cumulants of the psychometric function for order, as the general model implies. Some data confirm the model when examined in this way, but others do not. We consider extensions of the model from order judgments to other perceptual domains in which the relative arrival time of a pair of signals is thought to determine the percept. An additivity test applied to binaural lateralization favors extending the model to that phenomenon, and suggests a new method for tracing information flow in sensory channels by analyzing time-intensity trading relations at different "levels." Such an analysis reveals different effects of stimulus intensity on latency for different visual tasks, and leads to speculations about the locus of steroscopic depth perception in relation to other processes (Section V).

The influence of attentional bias on the point of subjective simultaneity makes tests of the model difficult. However, the model suggests how to study this "prior-entry" phenomenon and determine whether attention influences the sensory channels or the decision mechanism (Section VI).

Implications of transitivity of perceived order are examined, particularly in relation to the idea of a single multisensory "simultaneity center" in the brain; some experimental tests of transitivity are reviewed (Section VIII).

The problem of perceived order of three or more stimuli bears on several important questions, including transitivity. But existing experiments with multiple stimuli shed little light on these issues (Section IX).

Several aspects of experimental method are considered (Section X).