ENCODING OF ACOUSTIC DIRECTIONAL INFORMATION BY SACCULAR AFFERENTS OFTHE SLEEPER GOBY, DORMITATOR LATIFRONS

This paper reports on directional response properties of saccular affe rents of the sleeper goby, Dormitator latifrons, to 100-Hz acoustic pa rticle motions with a focus on testing the hypothesis that the respons e directionality of a fish's auditory afferents derives from the morph ological polarity of sensory hair cells in the otolithic organs. Spont aneous rates (SR) and best sensitivities (BS) of saccular afferents ra nged from 0 to 162 spikes/sec and from 0.2- to 100-nm RMS displacement . SR did not vary with BS. Most saccular afferents were phase-locked t o sinusoidal stimulation and had sustained temporal response patterns with some adaptation. All saccular afferents were directionally sensit ive to the stimulus, and the sharpness of directional response curves was determined by a directionality index (DI). The DI ranged from 0.64 to 1.50 (mean = 1.02, SE = 0.02, n = 100) and gradually decreased wit h stimulus level throughout afferents' response dynamic range. Many af ferents had approximately symmetric directional response curves relati ve to their best response axes (BRA). BRA of most afferents remained c onstant with stimulus level. The BRA distribution had a peak along an axis that correlates closely with the morphological polarity of saccul ar hair cells. Therefore, our results strongly support the hypothesis.