Acoustic elements of speechlike stimuli are reflected in surface recorded responses over the guinea pig temporal lobe

Auditory evoked potentials measured from the guinea pig temporal lobe surface reflect acoustic elements of synthesized speech syllables. Eliciting stimuli included a four formant anchor stimulus /ba/, with a 40-ms formant transition duration. The other stimuli differed from /ba/ along simple acoustic dimensions. The /pa/ stimuli differed on a VOT continuum; /da/ stimuli had a higher frequency F2 onset; /wa/ had a longer (80 ms) formant transition duration; and /bi/ differed in three vowel formant frequencies. The /ba/ and /da/ onset response latencies decreased systematically with increasing F2 onset frequency. The response to the /pa/ voicing increased in latency with increasing VOT and showed a physiologic discontinuity at VOT of 15-20 ms. Responses to /ba/ and /wa/ showed similar onset morphology but significant amplitude differences at latencies corresponding to vowel onset. Significant amplitude differences in /ba/ and /bi/ responses corresponded in latency to both consonant and vowel portions of the syllables. Similar to previous reports in the awake monkey for VOT, these results demonstrate in the anesthetized guinea pig that acoustic elements essential to speech perception are reflected in aggregate response of ensembles of cortical neurons.