We provide a summary of our recent research on the control of rapid
action sequences in speech production, emphasizing findings about the
advance planning and hierarchical organization of such sequences. The
effects of number of elements in the utterance (its "length") and other
factors on maximum production rates of short utterances lead us to
infer that a "motor program" for the whole utterance, prepared in
advance, controls the execution of each of its "units". Findings from
studies of typewriting as well as speech production have led us to a
model in which the performance of each unit is controlled by two
processes arranged in sequence: one (subprogram selection)
whose duration increases linearly with sequence length, and the other
(command) whose duration depends on type of unit.
Quantitative aspects of the production of utterances composed of
different types of element suggest that the action unit in speech is
the stress group or metrical foot. The virtual identity of the timing
of word and nonword utterances implies that the utterance program is
sufficiently detailed so it can be executed without reference to
learned routines for words stored elsewhere in memory.
We review our search for properties of performance that are suggested
by the model: First, the time from a reaction signal to the first unit
(the latency) increases linearly with utterance length. Second, the
maximum length utterance controlled by one program depends on unit
size. Third, the effect of utterance length on production timing is
localized (intermittent), rather than affecting all parts of the
articulatory stream. And fourth, the effect of utterance length on
production timing appears in just one epoch per unit.