Mechanisms of directional hearing in toadfish (Opsanus tau)

Abstract

Neurophysiological experiments on toadfish indicate the different strategies by which toadfish localize sources in azimuth and elevation. The saccules of the toadfish respond with great sensitivity to acoustic particle motion in the manner of inertial accelerometers. The directional response properties of otolithic afferents were studied in the horizontal and mid-sagittal planes using a 3-D shaker system. Most primary afferents have a cosine directionality response pattern. In the horizontal plane, an afferent’s best azimuthal direction is determined primarily by the orientation of the otolith organ in the head, and azimuth could be encoded as interaural response differences deriving from each organ’s gross directionality. The elevation of the axis of particle motion could be represented by a within-organ pattern of response magnitude over the afferent array that is determined by the patterns of hair cell orientation. In humans, source elevation can be estimated from the head-related transfer function, a monaural computation based on tonotopy. In toadfish, the saccule is not organized tonotopically, but directly with respect to the elevation of most effective particle motion. Thus, sound localization in fishes could be based on mechanisms of monaural and binaural computation substantially similar to those operating in other vertebrates. [Work supported by NIH and NIDCD.]