Rate and timing cues associated with the cochlear amplifier: Level discrimination based on monaural cross-frequency coincidence detection

The perceptual significance of the cochlear amplifier was evaluated by pred icting level-discrimination performance based on stochastic auditory-nerve (AN) activity. Performance was calculated for three models of processing: t he optimal all-information processor (based on discharge times), the optima l rate-place processor (based on discharge counts), and a monaural coincide nce-based processor that uses a non-optimal combination of rate and tempora l information. An analytical AN model included compressive magnitude and le vel-dependent-phase responses associated with the cochlear amplifier, and h igh-, medium-, and low-spontaneous-rate (SR) fibers with characteristic fre quencies (CFs) spanning the AN population. The relative contributions of no nlinear magnitude and nonlinear phase responses to level encoding were comp ared by using four versions of the model, which included and excluded the n onlinear gain and phase responses in all possible combinations. Nonlinear b asilar-membrane (BM) phase responses are robustly encoded in near-CF AN fib ers at low frequencies. Strongly compressive BM responses at high frequenci es near CF interact with the high thresholds of low-SR AN fibers to produce large dynamic ranges. Coincidence performance based on a narrow range of A N CFs was robust across a wide dynamic range at both low and high frequenci es, and matched human performance levels. Coincidence performance based on all CFs demonstrated the "near-miss" to Weber's law at low frequencies and the high-frequency "mid-level bump." Monaural coincidence detection is a ph ysiologically realistic mechanism that is extremely general in that it can utilize AN information (average-rate, synchrony, and nonlinear-phase cues) from all SR groups. (C) 2001 Acoustical Society of America.