Rods respond linearly to stimuli whose dynamic contrast is similar to that of natural scenes

Tothu (Tania) Vu, Sean T. McCarthy, W. Geoffrey Owen

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Purpose: The reflectances of natural objects fall within a narrow range (Krinov, '54) suggesting that the range of contrasts in a natural scene is similarly limited, (Shapley et al. '83). Small incremental flashes superimposed on any background elicit linear current responses in rod photo receptors. We test the hypothesis that when presented with light that is dynamically modulated about a mean intensity and whose contrast varies within the range encountered in a natural scene, the rod photocurrent is a linear transformation of the stimulus. Methods: We systematically measured light intensities in a variety of natural environments using a photometer equipped with a narrow-field detector. We then exposed solitary rods, isolated mechanically from the tiger salamander retina, to dynamic stimuli whose contrast varied within the measured limits, while recording the rod's circulating current with a suction pipette, (Baylor et al. 79). The light source was a narrow-bandwidth green LED modulated either by a Gaussian white noise or by a random waveform whose power spectral density varied as I/o)2. Results: We calculated the contrasts, (C = 1(1 - ImeanXImaan)l). in the ten different natural environments we examined. Of 220 samples taken, 89% had a contrast, ICI,

Original languageEnglish (US)
JournalInvestigative Ophthalmology and Visual Science
Issue number4
Publication statusPublished - 1997
Externally publishedYes


ASJC Scopus subject areas

  • Ophthalmology

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