A cross-linguistic examination of cortical auditory evoked potentials for a categorical voicing contrast.

Behavioral perceptions and cortical auditory evoked potentials (CAEPs) from native English (N=10) and Spanish speakers (N=10) were recorded for speech stimuli that constitute phonetically relevant categories of voicing. The stimuli were synthesized bilabial stop consonant-vowel syllables in a continuum ranging from/ba/to/pa/that varied in voice onset time (VOT) from 0 to 60 ms. Different behavioral perceptions were evidenced by significantly different categorical phonetic boundaries between the two groups (p<.0001). In contrast, there were no significant differences in CAEP component P1, N1, and P2 mean latencies or P1-N1 and N1-P2 amplitudes between groups (p>.05). Peak P1, N1, and P2 response latencies and P1-N1 and N1-P2 amplitudes increased significantly with increasing VOTs (p<.0001 and p<.001, respectively). There were no systematic changes in CAEP morphology that corresponded to listeners' perceptual categorical boundaries. These findings are consistent with the notion that changes in morphology of the P1-N1-P2 response are related to acoustical changes in speech sounds and are independent of phonetic categorization of voicing cues across language groups.