Eyes over ears? Bats as neuroethological models for understanding visual capture

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How we perceive the world depends on the environmental information available to our senses and our brain's ability to integrate the resulting neural information into a unified experience. My long-term objective is better understand how animals - vertebrates and invertebrates alike - use sensory information to construct internal representations of their often changing external environments. Over the course of this 5-year research grant, I will use bats to investigate how they and other vertebrates, including ourselves, combine visual and auditory information to build representations of the spatial arrangements of objects in our surroundings. Such representations are important for orientation and object recognition and are used to make decisions about what to eat, what to avoid, who to court, and how to get home. Among the senses, vision and hearing have most in common and the greatest potential for similarity in the way the brain represents the information gathered through them. For this same reason, if visual and auditory information are contradictory there is potential for confusion, especially if the brain cannot quickly decide which is the more accurate and reliable source.* For many birds and mammals, when auditory and visual information do not agree, the brain often chooses visual over auditory information to localize objects. Several explanations, none mutually exclusive, have been suggested to account for this. One is historical - because vision precedes hearing in the evolution of vertebrates, vision has had a greater impact on the evolution of hearing than hearing has had on vision. A second is developmental - suggesting that as the brain develops the visual system has a disproportionate influence on how the auditory system builds images of the outside world. A third postulates that the brain makes real-time estimations on the relative value of available visual and auditory information. This last explanation implies that visual dominance largely results because for much of the time for many animals visible light is more reliable than audible sound. Testing these different hypotheses using bats as subjects is the focus of my research proposal.* Bats have evolved to operate under the cover of night. The majority of today's species, through extraordinary adaptations to their auditory and vocal systems, are able to `see' with their ears. As a result of laryngeal echolocation, bats can do things that non-echolocating animals cannot do using sound: based on the echoes from their calls they can accurately determine an object's distance and also its size, shape, and texture. Bats are not blind, but because many species rely more on echoes than light for orientation, bats provide an excellent opportunity to study how the mammalian brain builds visual and auditory images and how evolution, development, and current environmental conditions each impact how mammals, faced with conflicting information, decide which sense to rely on.* Evolution, development, and current conditions must all exert an influence on how vertebrates prioritize and integrate audio-visual information. I will conduct behavioural, comparative, and neuroanatomical studies to disentangle their roles. I have also designed experiments to see if some bats are capable of cross-modal recognition. That is do bats perceive through echolocation images similar to those perceived through vision? In meeting these short-term objectives, my research will add to our understanding of how animals build coherent internal representations of the world around them. Ultimately, the results may help us to better comprehend aspects of the autism spectrum and schizophrenia, disorders associated with difficulties in integrating sensory information.