Acoustic change complex using short duration stimuli in normal hearing children: temporal resolution and frequency discrimination 

Objective: Acoustic Change Complex (ACC) is a cortical auditory evoked potential elicited in response to a change in an ongoing sound. Since it is supposed to reflect auditory discrimination at the cortical level, recording of this potential has recently gained much attention. From a technical standpoint, the stimulus used should be long enough to accommodate the needed change. This research addresses the development and standardization of short duration tonal stimuli which can be implemented in most of the Evoked Potential (EP) equipment used in regular Audiology clinics. Methods: Short duration tonal stimuli (500 msec.) were generated and edited using Audacity software. Temporal change was done using gap-in-tones stimuli (6, 10, 30 and 50 msec. in 1000 Hz tone). Frequency change was represented by frequency pairs (2%, 4%, 10% and 25% change from 1000 Hz base frequency). The developed stimuli were then used to generate ACC potential in 41 normal hearing children ranging in age from 2 to 10 years. A comparison was held between ACC response recorded using the different stimuli in reference to percent identifiability, morphology, latency and amplitude measures. Results: Gap-in-tones at 10 msec. and 4% frequency change could elicit ACC response in 100% of subjects. ACC had the same morphology of the onset response in the majority of subjects, with longer latency and smaller amplitude. ACC amplitude was consistently affected by magnitude of change. Conclusion: ACC was successfully recorded in 100% of normal hearing children using the developed short duration tonal stimuli for temporal change (10 msec.) and frequency change (4%). These stimuli can be uploaded in clinical EP equipment. ACC amplitude could be a better indicator of cortical discrimination compared to latency.