Overt and covert aspects of adult speech perception.

The relationship between verbal report and cardiac orienting response measures of speech discrimination in adult listeners was examined in two experiments using stimuli and paradigms previously employed in studies of infant speech perception. The results of Experiment I revealed that all listeners, those who reported discrimination of a synthetic [ba-ga] change (Group D) as well as those who did not (Group ND), demonstrated cardiac discrimination of the stimulus shift. However, this pattern of cardiac activity, both at stimulus onset and the shift, was found to be different in these two groups of listeners. Experiment II replicated the Group D results using a slightly different cardiac paradigm and quasinatural speech syllables. The implications of these findings for developmental research on speech perception with older infants, children, and populations with language disorders are discussed.