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Two signals in the human rod visual system: A model based on electrophysiological data

Published online by Cambridge University Press:  02 June 2009

Andrew Stockman
Affiliation:
Department of Psychology, University of California San Diego, La Jolla
Lindsay T. Sharpe
Affiliation:
Forschungsstelle für Experimentelle Ophthalmologie, University of Tübingen, D-72076 Tübingen, Germany
Klaus Rüther
Affiliation:
Pathophysiologie des Sehens und Neuro-Ophthalmologie, Universitäts-Augenklinik, University of Tübingen, D-72076 Tübingen, Germany
Knut Nordby
Affiliation:
Norwegian Telecommunications Administration, Research Department, N-2007 Kjeller, Norway

Abstract

In the human rod visual system, self-cancellation of flicker signals is observed at high rod intensity levels near 15 Hz, both perceptually and in the electroretinogram (ERG). This and other evidence suggests that two rod signals are transmitted through the human retina with different speeds of transmission. Here we report a series of flicker ERG recordings from a normal observer and an observer who lacks cone vision. From these results, we propose a quantitative model of the two rod signals, which assumes (1) that the amplitude of the slow signal grows linearly with log intensity but then saturates at ~1 scot, td; (2) that the amplitude of the fast signal grows linearly with intensity; (3) that there is a difference in time delay of ~33 ms between two rod signals of the same polarity (or of ~67 ms if the signals are of inverted polarity); and (4) that the time delay of both signals declines linearly with log intensity (by ~10 ms per log scot. td). These simple assumptions provide a remarkably good account of the experimental data. Our results and model are relevant to current anatomical theories of the mammalian rod visual system. We speculate that the slower signal in the human ERG may reflect the transmission of the rod response via the rod bipolars and the An amacrine cells, while the faster signal may reflect its transmission via the rod-cone gap junctions and the cone bipolars. There are, however, several objections to this simple correspondence.

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Type
Research Articles
Copyright
Copyright © Cambridge University Press 1995

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