Retinal bipolar cells: Contrast encoding for sinusoidal modulation and steps of luminance contrast
Contrast encoding for sinusoidal modulations of luminance contrast was investigated by intracellular recording in the intact salamander retina. In what appears to be the first study of this kind for vertebrate bipolar cells, responses of the central receptive-field mechanism of cone-driven cells to...
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Published in | Visual neuroscience Vol. 21; no. 6; pp. 883 - 893 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
New York, USA
Cambridge University Press
01.11.2004
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Subjects | |
Online Access | Get full text |
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Summary: | Contrast encoding for sinusoidal modulations of luminance contrast
was investigated by intracellular recording in the intact salamander
retina. In what appears to be the first study of this kind for
vertebrate bipolar cells, responses of the central receptive-field
mechanism of cone-driven cells to modulation of 3 Hz were analyzed
quantitatively via both signal averaging and a Fast Fourier
Transform (FFT) while the retina was light adapted to 20
cd/m2. Depolarizing and hyperpolarizing bipolar cells
showed very similar encoding. Both responded with sinusoidal waveforms
whose amplitude varied linearly with modulation depths ranging up to
7–8%. The slope of the modulation/response curve was very
steep in this range. Thus, the contrast gain was high, reaching values
of 6–7, and the half-maximal response was achieved at modulations
of 9% or less. At modulations above ∼15%, the responses typically
showed strong compressive nonlinearity and the waveform was
increasingly distorted. At maximum modulation, the higher harmonics of
the FFT constituted about 30% of the amplitude of the fundamental.
Measurements were also made for cones and horizontal cells. Both cell
types showed predominantly linear responses and low contrast gain, in
marked contrast to bipolar cells. These results suggest that the high
contrast gain and strong nonlinearity of bipolar cells largely arise
postsynaptic to cone transmitter release. Further experiments were
performed to compare responses to contrast steps versus those to
sinusoidal modulation. In the linear range, we show that the contrast
gains of cones and horizontal cells are low and virtually identical for
both steps and sinusoidal modulations. In bipolar cells, on the other
hand, the contrast gain is about two times greater for steps than that
for the 3-Hz sine waves. These results suggest that mechanisms
intrinsic to bipolar cells act like a high-pass filter with a short
time constant to selectively emphasize contrast transients over slower
changes in contrast. |
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Bibliography: | istex:6881B0422C42AFBA1ECE6FDE001650BDC783EBE7 PII:S095252380421608X ark:/67375/6GQ-8Q44RRVL-5 ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23 ObjectType-Article-1 ObjectType-Feature-2 |
ISSN: | 0952-5238 1469-8714 |
DOI: | 10.1017/S095252380421608X |