Source localization in underwater sound fields

We investigated the acoustical information present in the field of arbitrary sound sources which may provide direction and distance to the source from a local reading of the sound field parameters. If the effects of reflections are negligible, the particle acceleration is directed radially at the instant of sound pressure nulls. The spectral relation between the radial component of the particle aceleration and the sound pressure is characterized by a critical frequency where a sharp transition occurs in the amplitude ratio and the phase relation of these variables. The critical frequency depends on the distance to the source and depends little on the source type (mono-, di- or quadrupole). Thus, a local reading of the particle acceleration and the sound pressure is in principle sufficient to localize the sound source in three dimensions. Fish might use this kind of information for acoustic orientation

Auditory development and multi-sensory integration in the round goby, Neogobius melanostomus

Most animals rely on the integration of information from a number of external sources. Auditory cues can help fish find mates, food and shelter. However, despite all the time spent and the advances in technology that have been made since the 1938 discovery that fish could hear, some questions regarding fish audition have remained unanswered. The main objective of my thesis was to answer some of these fundamental questions and to further our scientific understanding of fish hearing. The first main objective of my thesis was to investigate how auditory thresholds change over the development of a fish. In chapter 1, I examined auditory structure and function in the round goby (Neogobius melanostomus) to ascertain how developmental changes may influence hearing ability. In the second chapter of this dissertation, I investigate how the morphology of auditory and mechanosensory systems can be used to explain a fish\u27s ability to localize sound. I suggest that the overall position of the otoliths and hair cells in the head of the round goby, along with the extensive array of neuromasts on the head both contribute to the localization abilities of this species. In the third data chapter, I investigated the physiological response of the round gobies to conspecific and heterospecific vocalizations. Responding to the vocalizations of a conspecific can help an individual locate food, shelter and mates. The results of this study indicate that on a physiological level, round gobies are able to distinguish their own vocalizations from those of heterospecifics. In the final chapter, I investigated the use of multi-sensory integration in fish. In their aquatic environment, fish receive information from a number of biologically relevant objects. The results from both physiological and behavioural trials to assess the role of visual and olfactory cues in response to auditory stimuli in the round goby (Neogobius melanostomus ) suggest the use of multi-sensory integration in this species. Combined, all of these characteristics made the round goby an ideal model for investigating auditory development, morphology and multi-sensory integration