The effects of very slow rates of stimulus presentation on event-related potential estimates of hearing threshold.

The present study evaluated the use of slow rates of stimulus presentation on the accuracy of the N1-P2 cortical response in estimating hearing threshold. Long interstimulus intervals (ISI) allow the non-specific component of the N1 response to emerge, believed to reflect widespread cortical arousal that facilitates sensory and motor responses. We examined whether the non-specific N1 would be elicited at intensity levels near threshold. Event-related potentials were recorded to 0.5-, 1.0, and 4.0-kHz tone bursts with a long ISI (8-12 s) while the eleven subjects read a book. The stimulus level varied from -5 to 45 dB nHL. The 1.0-kHz tone burst was also presented with a shorter ISI (1.5-2.5 s), akin to that typically used in the audiological setting. The amplitude of N1-P2 was significantly enhanced in the long compared to short ISI condition, but, importantly, only for the stimuli with a level > or =25 dB nHL. Therefore, the N1-P2 recorded with long ISIs was not more precise in estimating threshold than that recorded with short ISIs, remaining visible to within 10 dB of behavioural threshold.