Coding of consonant-vowel transition in children with central auditory processing disorder: an electrophysiological study.

INTRODUCTION: Acoustic change complex (ACC) is an important tool to investigate the encoding of the acoustic property of speech signals in various populations. However, there is a limited number of research papers that have explored the usefulness of ACC as a tool to study the neural encoding of consonant-vowel (CV) transition in children with central auditory processing disorder (CAPD). Thus, the present study aims to investigate the utility of ACC as an objective tool to study the neural representation of consonant-vowel (CV) transition in children with CAPD. METHODS: Twenty children diagnosed having CAPD and 20 normal counterparts in the age range of 8-14 years were the participants. The ACC was acquired using naturally produced CV syllable /sa/ with a duration of 380 ms. RESULTS: Latency of N1' and P2' was found to be prolonged in children with CAPD compared to normal counterparts, whereas the amplitude of N1' and P2' did not show any significant difference. Scalp topography showed significantly different activation patterns for children with and without CAPD. CONCLUSION: Prolonged latencies of ACC indicated poor encoding of CV transition in children with CAPD. The difference in scalp topography might be because of the involvement of additional brain areas for the neural discrimination task in children with CAPD.

Effect of pre-transition stimulus duration on acoustic change complex.

OBJECTIVE: To investigate the effect of pre-transition duration on acoustic change complex (ACC) for speech and tonal stimulus. DESIGN: Cortical potentials were recorded for consonant-vowel syllable and tonal complex stimuli with varying pre-transition durations. STUDY SAMPLE: Ten individuals (three male and seven female) in the age range from 18 to 26 years, with normal hearing sensitivity, participated in the study. RESULTS: The results revealed that a minimum pre-transition duration of 100 ms for tonal stimulus (with spectral change) and 80 ms for consonant-vowel syllable is necessary in order to elicit ACC. The latency of N1(1) and P2(1), which is the response for change within the ongoing stimulus, increased with increase in pre-transition duration. The amplitude of the evoked responses did not show any significant change. CONCLUSIONS: It was found that minimum pre-transition duration required in eliciting ACC for speech and non-speech stimulus is not same. The speech stimulus required lesser duration of pre-transition than non-speech stimulus. Further studies regarding the acoustic aspects of sound on CAEP in isolation are warranted.