(NAS Colloquium) Vision From Photon to Perception (1999) / Chapter Skim
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Multineuronal codes in retinal signaling
Multineuronal codes in retinal signaling
Pages 53-58
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From page 53... ...
In the cat retina, for example, the coverage factors within each of the ON and OFF subdivisions range up to 3 for Y cells and up to 15 for X cells (7~. The conclusion that overlapping receptive fields imply redundant optic nerve signals results from the assumption that different neurons in the ganglion cell population operate independently of each other.
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From page 54... ...
The efficiency of monitoring a large number of cells and the long lifetime of the amphibian preparation have allowed a more thorough statistical analysis of concerted firing patterns, as well as an assessment of their role in visual signaling. During spontaneous activity in darkness, nearby ganglion cells had a pronounced tendency to fire synchronously, within 10-20 ms of each other (Fig.
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From page 55... ...
To what extent is a combinatorial multiunit code beneficial at all, compared with a system that simply uses independent ganglion cells with large and overlapping receptive fields? Could the same information about the visual scene be extracted from the spike trains of two independent ganglion cells, without an explicit encoding of the receptive field subunits deriving from amacrine cells?
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From page 56... ...
It was argued above that the visual input to the retina, after transduction by photoreceptors, varies on a time scale much longer than the coincidence interval within which ganglion cells exhibit synchronous firing. This can be incorporated in a more realistic analysis by holding the stimulus steady for N time units, and collecting the N resulting firing patterns as the response (Fig.
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From page 57... ...
Closer analysis showed that the enhanced spatial acuity of network A results because its concerted firing patterns explicitly represent the activities of retinal interneurons, each of which has a smaller receptive field than the ganglion cells. Thus, the output of network A represents three independent samples of the visual scene, whereas the output of B contains only two independent samples.
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From page 58... ...
Such a representation may be more adapted to the requirements for subsequent neural processing. Whether such decoding of concerted firing patterns does in fact occur must be resolved by future experiments which will provide a critical test of the retinal coding mechanisms proposed here.
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