Acoustic Change Complex (ACC) using Speech and Non-Speech Stimuli in Normal Hearing Children

Abstract Background Cortical auditory evoked potentials (CAEPs) are brain responses evoked by sound and are processed in or near the auditory cortex. ACC is a cortical auditory evoked potential (P1-N1-P2) elicited by a change within an ongoing sound stimulus. Objective To reach the best stimuli that can elicit ACC and act as an objective tool for assessment of cortical auditory discrimination in normal hearing children. Patients and Methods The present study was originally designed to standardize ACC evoked response in 41 children aged from 2 to 10 years. The mean age in our study group was 6.2 years with no significant difference between males and females. Stimuli used in this study were specifically designed to be used by AEP equipment that is capable of uploading short duration stimuli (500 msec.), thus can be used in a regular AEP lab. ACC was elicited by three groups of stimuli. Gap-in-tones stimuli represent temporal change (6, 10, 30 and 50 msec. gap introduced to 1000 Hz tone separately), frequency pairs stimuli represent frequency change (2%, 4%, 10% and 25% change from base freq. 1000 Hz) and vowel pairs stimuli represent spectral change (/i-u/, /u-i/, /i-a/. /a-i/, /u-a/, /a-u/). ACC response parameters were compared when using the different stimuli as regards percent detectability, morphology, latency and amplitude. Results Gap-in-tones at 6 msec. and 4% frequency change could elicit ACC response in 100% of subjects. For spectral change, /u-i/ was the highest in eliciting ACC (78%) followed by /i-u/ (68.2%) then /a-i/ (58.5%). ACC had the same morphology of the onset response in the majority of subjects, with longer latency and smaller amplitude. ACC amplitude is a better indicator of cortical discrimination compared to latency because it is consistently affected by magnitude of change. Conclusion ACC is a good electrophysiological tool for cortical auditory discrimination for temporal, frequency and spectral change.