Scene analysis, or the mental parcellation of complex sensory input into representations of external objects, is the central task of any sensory system. Sensory stimuli can only inform behavior if the nervous system can distinguish between irrelevant background noise and important stimulus sources, and each source must be distinguished both from noise and from other possibly relevant sources. The goal of research in sensory science is to explain how this task is accomplished and to identify stimuli that allow an animal to direct appropriate behaviors. The present study addresses this problem for two important detectors of vibratory stimuli -- the inner ear and the closely related lateral line system of fishes. Unlike the majority of existing studies of these systems, which have been performed against a quiet background, this proposal measures the ability to detect spatially discrete signals and discriminate source location in both quiet and noisy settings. The mammalian sense of hearing (in air) relies only on the detection of pressure fluctuations, but for most aquatic animals, the sensory systems that detect vibratory sources provide information not only about the propagating pressure wave, but also two other aspects of the sound field surrounding a vibratory source: The acceleration detected by inertial sensors of the inner ear; and the pattern of water motions detected by the lateral line. Thus each of these sensors responds to the same stimuli, but detects different physical aspects of the stimulus. This study will test the importance of multisensory interaction in the perception of the natural environment, focusing on how each sensory channel contributes to a perception of source location. This proposal will also develop the octavolateralis system (hearing and lateral line senses) as a model of multisensory complementation, much like human touch relies on complementation between texture, pressure, and vibration sensory channels. Multisensory processing is ubiquitous and one important feature of our experimental approach is the use of natural stimuli (vibratory dipoles) that are more effective than loudspeakers for stimulating multiple hearing-related submodalities. An improved understanding of how multiple sensory systems combine to create unitary percepts will lead to better rehabilitation strategies following partial sensory loss.
