ABSTRACT
The hypothesis that fish may remove 180° ambiguities concerning the sound source direction by a timing analysis between particle motion components is addressed. Analysis of the phase difference ψ (w, v) between the horizontal (v) and the vertical (w) components of the particle velocity of sound signals by teleost fish is investigated by cardiac conditioning. Standing wave sound stimuli (90 Hz) are used with ψ (w, v) = + or – 90° and equal amplitudes of v and w. The water particles move along circular trajectories for such stimuli: however, the direction of revolution is reversed in the two stimuli. These stimuli were discriminated by one whiting, one catfish and several cod, indicating that these teleosts are able to discriminate signals on a pure timing cue. If the w/v ratio is lowered, the cod can discriminate the resulting elliptical motions on the direction of revolution down to a w/v ratio of –12 dB. Moreover, down to the same w/v ratio the cod discriminates an elliptical particle motion signal from a pure translatory particle motion signal. At this level, the threshold signal-to-noise ratio for the w component is exceeded by 9 dB. Apparently phase analysis can be limited by ‘cross talk’ between horizontal and vertical particle motion detectors. The results are discussed with respect to models of directional hearing by fish.
