ADAPTATION OF RETINAL PROCESSING TO IMAGE-CONTRAST AND SPATIAL SCALE

Citation
Sm. Smirnakis et al., ADAPTATION OF RETINAL PROCESSING TO IMAGE-CONTRAST AND SPATIAL SCALE, Nature, 386(6620), 1997, pp. 69-73
Citations number
28
Categorie Soggetti
Multidisciplinary Sciences
Journal title
NatureACNP
ISSN journal
00280836
Volume
386
Issue
6620
Year of publication
1997
Pages
69 - 73
Database
ISI
SICI code
0028-0836(1997)386:6620<69:AORPTI>2.0.ZU;2-E
Abstract
Owing to the limited dynamic range of a neuron's output, neural circui ts are faced with a trade-off between encoding the full range of their inputs and resolving gradations among those inputs. For example, the ambient light level varies daily over more than nine orders of magnitu de(1), whereas the firing rate of optic nerve fibres spans less than t wo(2). This discrepancy is alleviated by light adaptation(3): as the m ean intensity increases, the retina becomes proportionately less sensi tive. However, image statistics other than the mean intensity also var y drastically during routine visual processing. Theory predicts that a n efficient visual encoder should adapt its strategy not only to the m ean, but to the full shape of the intensity distribution(4-6). Here we report that retinal ganglion cells, the output neurons of the retina, adapt to both image contrast-the range of light intensities-and to sp atial correlations within the scene, even at constant mean intensity. The adaptation occurs on a scale of seconds, one hundred times more sl owly than the immediate light response, and involves 2-5-fold changes in the firing rate. It is mediated within the retinal network: two ind ependent sites of modulation after the photoreceptor cells appear to b e involved. Our results demonstrate a remarkable plasticity in retinal processing that may contribute to the contrast adaptation of human vi sion(7).