Background: Acoustic change complex (ACC) is an auditory-evoked cortical potential elicited for a change in the physical properties of the sound. It can be elicited for a change in frequency, amplitude, or periodicity in the ongoing speech and nonspeech stimuli. Earlier investigations have established a significant effect of stimulus-related factors on the cortical auditory-evoked potentials. However, investigations to understand the effects of stimulus factors on the ACC are rare. Purpose: This study aimed to investigate the effect of inter-stimulus interval (ISI) between the stimuli on the ACC elicited for speech and tone-complex stimuli. Research Design: This is a cross-sectional study. Method: A total of 12 young adults aged between 18 and 22 years with normal hearing in both ears participated in the study. The ACC was elicited using a consonant-vowel syllable/sa/and frequency-changing tone-complex. Tone-complex had an onset frequency of 1000 Hz and changed its frequency to 2000 Hz at 120 ms after the onset. Both stimuli had a total duration of 350 ms and changed their characteristics at 120 ms after the onset. The stimulus was presented monaurally with ISIs of 500, 1000, 1500, and 2000 ms, and the ACC was recorded from Cz to Fz. Results: The present study showed a significant effect of ISI on peak latencies and peak-to-peak amplitudes. Shorter ISI was found to elicit peaks with smaller amplitude and slightly longer latency, whereas longer ISI elicited peaks with larger amplitude and shorter latency. Further, the amplitude of response for tone-complex was larger than response for syllable/sa/. Conclusions: ISI is one of the stimulus-related factors which significantly affects the ACC. Longer ISIs (≥1500 ms) should be used to elicit the ACC.
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