Effects of attention on cortical auditory evoked potentials during a gap detection task

Gap-detection testing is a measure of temporal resolution, a component of auditory processing that is sometimes affected in Central Auditory Processing Disorder (CAPD). Using behavioural gap-detection tasks as part of a CAPD battery can be confounded by attention, in that it is difficult to distinguish whether poor performance is a result of attention deficits or central auditory processing deficits. Researchers have assessed the utility of cortical auditory evoked potentials (CAEPs) as an objective measure of gap-detection thresholds. The present study aimed to compare CAEPs during a passive and active gap-detection task to assess the effects of attention on electrophysiological gap-detection testing. The results showed no significant differences in gap-detection thresholds obtained behaviourally, obtained electrophysiologically during the passive task, and obtained behaviourally or electrophysiologically during the active task. N1-P2 amplitudes were found to be significantly larger in the active gap-detection task compared to the passive task. In conditions where a 0 ms duration or subthreshold duration gap was presented, an N2b waveform was evoked. The N2b is an endogenous event-related potential (ERP) that is usually evoked when a prepotent response must be withheld, such as during the no-go trials of a go/no-go task. Because the gap-detection task could be considered as a go/no-go paradigm, the N2b was likely evoked due to the unfulfilled expectation of a gap occurring with predictable timing and high probability. The goal of experiment 2 was to investigate the occurrence of this endogenously-evoked no-go N2b as previous literature has focused primarily on the N2b evoked by exogenous stimuli. The results found that all participants had an N2b wave to no-gap and subthreshold gap conditions. There were no significant correlations between N2b-P3a amplitudes and behavioural thresholds or between N2b-P3a amplitudes or N2b latencies and reaction time or reaction time standard deviation. There was a significant correlation between P3a amplitudes and ex-Gaussian reaction time standard deviation. No significant differences were found between N2b amplitudes for correct rejections or misses. Overall, this study demonstrated that the no-go N2b can be evoked by an endogenous signal in the form of the omission of an expected gap in noise.Medicine, Faculty ofAudiology and Speech Sciences, School ofGraduat