Auditory evoked-potential correlates of decrement detection

Decrement detection is a commonly used psychophysical technique in which a subject is required to detect partially filled gaps in an ongoing sound. The paradigm provides information regarding both temporal resolution and intensity discrimination. The purpose of this project was to determine if an evoked-potential paradigm using decrements in an ongoing noise approximates psychophysical data. If so, the evoked-response paradigm would be useful in estimating decrement detection in laboratory animals, where training time for a psychophysical model of decrement detection might prove prohibitive. In this study, Mongolian gerbils aged 3–10 months were used as subjects. The stimulus was a broadband noise (low-pass filtered at 5 or 30 kHz, overall level of 70 dB SPL), interrupted for durations of 2–32 ms. Within each off period, a second, identically filtered noise at levels of 0–70 dB SPL was presented. In a manner qualitatively similar to previous human and animal psychophysical studies, the ABR threshold decreased as the duration of the decrement was increased. Latency and amplitudes changed as a function of decrement duration when the decrement depth was held constant, but minimal change as a function of decrement depth occurred when the decrement duration was held constant. The results suggest that ABR paradigm for decrement detection is a qualitative alternative to psychophysical techniques, but that amplitude and latency data may not provide more information on temporal and intensity coding than ABR measures of gap detection.