Abstract
Models of how listeners understand speech must specify the types of representations that are computed, the nature of the flow of information, and the control structures that modify performance. Three experiments are reported that focus on the control processes in speech perception. Subjects in the experiments tried to discriminate stimuli in which a phoneme had been replaced with white noise from stimuli in which white noise was merely superimposed on a phoneme. In the first two experiments, subjects practiced the discrimination for thousands of trials but did not improve, suggesting that they have poor access to low-level representations of the speech signal. In the third experiment, each (auditory) stimulus was preceded by a visual cue that could potentially be used to focus attention in order to enhance performance. Only subjects who received information about both the identity of the impending word and the identity of the critical phoneme showed enhanced discrimination. Other cues, including syllabic plus phonemic information, were ineffective. The results indicate that attentional control of processing is difficult but possible, and that lexical representations play a central role in the allocation of attention.