Effect of Consonant Duration on Formation of Consonant-Vowel Syllable Evoked Auditory Cortical Potentials.

OBJECTIVE: To compare P1-N1-P2-N2 response latencies and amplitudes evoked by voiced and unvoiced consonant-vowel syllables (CVS) /bi/-/pi/ and /di/-/ti/ by analyzing how the cortical responses to consonants and vowels interact during the formation of a syllable-evoked response.

MATERIALS AND METHODS: Auditory late latency responses were recorded from 12 healthy individuals between the ages of 20 and 40 years with normal hearing while presenting /bi/-/pi/ and /di/-/ti/ tokens and individual consonant-vowel parts of syllables. Amplitude/latency values of P1-N1-P2-N2 responses were compared between /bi/-/pi/ and /di/-/ti/ pairs. Formation of CVS-evoked responses by consonant and vowel responses was also investigated.

RESULTS: N1-P2-N2 latencies evoked by /bi/ were significantly shorter than /pi/. P2-N2 amplitudes evoked by /di/ were significantly higher and N2 latencies were shorter than /ti/. N1-P2-N2 peaks of /bi/, /pi/, and /di/ seemed to be combinations of respective peaks of consonant and vowel-evoked responses. For /ti/, P1 and N1 seem to be stemming only from the consonant part, P2 from consonant P2 and vowel N1, and N2 from consonant N2 and vowel P2-N2.

CONCLUSION: For both CVS pairs, longer consonant durations resulted in lower amplitudes and/or longer latencies, and this sheds light on why voiced-unvoiced CVSs evoke cortical responses with different features. Obtaining evoked responses to each consonant-vowel part of the syllables among listeners with perceptual difficulties and hearing devices might help to reveal which acoustic cues are not well represented in the auditory brain.