Analysis of Auditory Evoked Responses Elicited by Gaps in Noise
Psychophysical detection of gaps embedded in ongoing sounds is commonly used to measure temporal resolution in hearing tests. Cortical auditory responses to such gaps in noise are investigated as electrophysiological assessment of temporal resolution. This study was conducted to investigate the characteristics of auditory evoked potentials (AEPs) to gaps in broadband noise. Transient responses such as Auditory Brainstem (ABR), Middle Latency (MLR) and Late latency (LLR) were recorded as well as 40Hz Auditory Steady-State Responses (ASSR) and Quasi ASSR generated by jittered 40Hz gaps. Gaps of short and long durations were presented at different rates to study the effect of rate and duration on AEPs. Also, the influence of gap onset/offset on the transient evoked responses was examined. AEPs were elicited at four rates 0.5, 1, 5, and 40Hz. 0.5Hz responses showed cortical waves while 1 Hz responses showed ABR, MLR and LLR components. 40 and 5 Hz responses were characterized by ABR and MLR components with no LLRs likely. For short gaps, results suggest that amplitudes of MLR, LLR and QASSR were affected by gap duration; as the duration decreases the amplitudes diminish. For long gaps, two distinct onset and offset responses were observed. Waveform changes as the gap shortens from 300ms to 6ms suggest overlap of the onset and offset responses resulting in different AEP morphologies.
