The Journal of Neuroscience, April 15, 2001, 21(8):2842-2850
Neuronal Population Codes and the Perception of Object Distance
in Weakly Electric Fish
John E.
Lewis and
Leonard
Maler
Department of Cellular and Molecular Medicine, University of
Ottawa, Ottawa, Ontario, Canada K1H 8M5
Weakly electric fish use an electric sense to navigate and capture
prey in the dark. Objects in the surroundings of the fish produce
distortions in their self-generated electric field; these distortions
form a two-dimensional Gaussian-like electric image on the skin
surface. To determine the distance of an object, the peak amplitude and
width of its electric image must be estimated. These sensory features
are encoded by a neuronal population in the early stages of the
electrosensory pathway, but are not represented with classic
bell-shaped neuronal tuning curves. In contrast, bell-shaped tuning
curves do characterize the neuronal responses to the location of the
electric image on the body surface, such that parallel two-dimensional
maps of this feature are formed. In the case of such two-dimensional
maps, theoretical results suggest that the width of neural tuning
should have no effect on the accuracy of a population code. Here we
show that although the spatial scale of the electrosensory maps does
not affect the accuracy of encoding the body surface location of the
electric image, maps with narrower tuning are better for estimating
image width and those with wider tuning are better for estimating image amplitude. We quantitatively evaluate a two-step algorithm for distance
perception involving the sequential estimation of peak amplitude and
width of the electric image. This algorithm is best implemented by two
neural maps with different tuning widths. These results suggest that
multiple maps of sensory features may be specialized with different
tuning widths, for encoding additional sensory features that are not
explicitly mapped.
Key words:
depth perception; electrolocation; electrosensory system; neuronal tuning; population coding; sensory coding
Copyright © 2001 Society for Neuroscience 0270-6474/01/2182842-09$05.00/0
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