COCHLEAR TUNING IN THE GERBIL - A COMPARISON OF RESPONSES TO SINUSOIDAL AMPLITUDE-MODULATION AND DIFFERENCE TONE STIMULI

Vocalizations often have periodic variations of their acoustic wavefor m envelope. Two simultaneously presented frequencies have an envelope fluctuation with a frequency equal to their difference tone (DT F-2-F- 1) Sinusoidal amplitude modulation (SAM) of a carrier frequency also p roduces an envelope fluctuation. Electrical ensemble responses to DT a nd SAM stimuli were recorded from the gerbil's round window. The predo minant frequency of the response to the DT stimuli is F-2-F-1; to the SAM stimuli, it is the modulation frequency. Both responses are spectr ally, temporally, and dynamically non-linear. Forward masking of a low -frequency DT response produced a tuning curve (TC) with a tip at the high-stimulus frequency. Forward masker TCs of a low-frequency SAM ens emble response had tips at the high frequency of the carrier. Tip thre sholds and sharpness of tuning of DT and SAM TCs are quite similar, wi th cochlear neurons having high characteristic frequencies providing s harply tuned information about low frequency acoustic envelope periodi cities.