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The extent to which a sensory system can distinguish two similar stimuli (two-point discrimination) provides a measure of the accuracy and reliability of sensory coding and subsequent production of behaviour. Weakly electric fish detect and recognize objects in the dark using an electric sense. Objects in the surrounding water distort the fish's self-generated dipole-like electric field. The profile of the resulting changes in voltage across their skin surface, the so-called electric image, is encoded by specialized electroreceptors and provides a basis for the electric sense. The physics of electric fields dictates that the electric image will be a blurry representation of the environment. To determine the perceptual consequences of this blurriness, we have experimentally tested two-point discrimination in electric fish. We find that the spatial resolution of electrosensory perception is close to the limit imposed by the blurry electric images. Through the exploration of simplified but physiologically-based neural models, we show that the dynamics of mixed excitatory-inhibitory feedback pathways in the electrosensory system can lead to improved discrimination performance in this perceptual task. |
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