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Noise and light adaptation in rods of the macaque monkey

Published online by Cambridge University Press:  15 December 2000

D.M. SCHNEEWEIS  and
J.L. SCHNAPF
D.M. SCHNEEWEIS
Affiliation:
Smith-Kettlewell Eye Research Institute, 2318 Fillmore Street, San Francisco
J.L. SCHNAPF
Affiliation:
Departments of Ophthalmology and Physiology, University of California, San Francisco
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Abstract

Membrane voltage was recorded in rod photoreceptors in retina isolated from macaque monkey. The size of the single photon response and the magnitude of membrane voltage fluctuations were assessed in dark- and light-adapted retina. The “dark light” rate ID, defined as the rate of spontaneous photopigment isomerizations that would produce a variance equivalent to that of the noise measured in the dark, was calculated after matched filtering. The average value of 0.08 s−1 fell at the higher end of psychophysical estimates of dark light in human observers. In light-adapted rods the photon response decreased in amplitude and duration, and the magnitude of the voltage fluctuations increased with increasing background light intensity. The signal-to-noise ratio (SNR) for single rods was defined as the ratio of the peak amplitude of the photon response to the standard deviation of the noise fluctuations. The signal-to-noise ratio for dark-adapted rods SNRD was about 7. With increasing background intensity I, the SNR fell as SNRD(1 + I/ID)−1/2. This function may account for the increment thresholds measured with small brief test flashes in human psychophysical experiments.

Keywords

Retinal rodsMacaque monkeySingle photon responseNoiseLight adaptation
Type
Research Article
Information
Visual Neuroscience , Volume 17 , Issue 5 , September 2000 , pp. 659 - 666
Copyright
2000 Cambridge University Press

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