Abstract
The objective of this study was to investigate the effect of stimuli, transducers and gender on the latency and amplitude of acoustic change complex (ACC). ACC is a multiple overlapping P1-N1-P2 complex reflecting acoustic changes across the entire stimulus. Fifteen males and 15 females, in the age range of 18 to 25 (mean=21.67) years, having normal hearing participated in the study. The ACC was recorded using the vertical montage. The naturally produced stimuli /sa/ and /si/ were presented through the insert earphone/loud speaker to record the ACC. The ACC obtained from different stimuli presented through different transducers from male/female participants were analyzed using mixed analysis of variance. Dependent t-test and independent t-test were performed when indicated. There was a significant difference in latency of 2N1 at the transition, with latency for /sa/ being earlier; but not at the onset portions of ACC. There was no significant difference in amplitude of ACC between the stimuli. Among the transducers, there was no significant difference in latency and amplitude of ACC, for both /sa/ and /si/ stimuli. Female participants showed earlier latency for 2N1 and larger amplitude of N1 and 2P2 than male participants, which was significant. ACC provides important insight in detecting the subtle spectral changes in each stimulus. Among the transducers, no difference in ACC was noted as the spectra of stimuli delivered were within the frequency response of the transducers. The earlier 2N1 latency and larger N1 and 2P2 amplitudes noticed in female participants could be due to smaller head circumference. The findings of this study will be useful in determining the capacity of the auditory pathway in detecting subtle spectral changes in the stimulus at the level of the auditory cortex.
Highlights
Speech evoked cortical auditory potentials are frequently used to study the cortical representation of speech sounds in the cortex
The underlying assumption is that speech perception is dependent on neural detection of time varying spectral and temporal cues contained in the speech signal
Central auditory evoked potentials (CAEPs) are evoked by brief stimuli such as clicks1 or tone burst,2 CAEPs can be elicited in response to natural speech stimuli3 that are longer in duration and contain time-varying acoustic cues
Summary
Speech evoked cortical auditory potentials are frequently used to study the cortical representation of speech sounds in the cortex. The underlying assumption is that speech perception is dependent on neural detection of time varying spectral and temporal cues contained in the speech signal. CAEPs are evoked by brief stimuli such as clicks or tone burst, CAEPs can be elicited in response to natural speech stimuli that are longer in duration and contain time-varying acoustic cues.. In addition to the CAEPs reflecting the neural detection in response to time-varying cues mentioned earlier, it reveals changes in amplitude, periodicity, changes in temporal cues (voice onset time of 60 ms), changes from a harmonic tonal complex to a noise band with the same spectral envelope and formant frequency changes alone in the ongoing vowels with no amplitude increment which suggests authors would like to acknowledge the reviewer for the valuable comments that the CAEPs reflect cortical detection of complex changes in ongoand Ms Joy Reddy for English editing
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