ASA 127th Meeting M.I.T. 1994 June 6-10

2aPP14. Temporal process model for periodicity extraction in frog auditory system.

Dept. of Psychol., Brown Univ., Providence, RI 02912

One simple time-domain demodulation model, equipped primarily with (1) a bandpass filter, (2) a nonlinear rectifier, and (3) a lowpass filter, has been contrived to test the suggestion that frog auditory nerve fibers encode periodicity by a temporal mechanism, rather than by a rate-place mechanism, as strongly indicated from physiological experiments [A. M. Simmons and M. Ferragamo, J. Comp. Physiol. 172, 57--69 (1993); A. M. Simmons et al., J. Acoust. Soc. Am. 93, 3374--3389 (1993)]. With one set of model parameters, this model can quantitatively replicate up to 80% of the periodicity extraction observed in all fibers stimulated with complex sounds. The sensitivity of the model to phase information has been examined through driving it with seven frequency-component stimuli with different phase combinations. Different intensities (+10, +20, and +30 dB above threshold) are employed to test the effect of nonlinear gain control and saturation on dynamic range. Extensive numerical simulation has been used to identify the optimal parameter set to maximally match model response with experimental results. Partitioning of fibers into different CF groups provided further insight between model parameters and physiological data. A short-term adaptation unit has been added to the model and tested with experimental data as well. [Work supported by NIH.]