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Marcus H. Howlett, Maarten Kamermans; Cones Modify Their Frequency Tuning Curve In Response To Contrast Due To Membrane Properties. Invest. Ophthalmol. Vis. Sci. 2012;53(14):772.
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© ARVO (1962-2015); The Authors (2016-present)
In natural scenes light intensity and contrast are statistically independent. The visual system seems to utilize this phenomenon as adaptive mechanisms for luminance and contrast operate independently in many classes of visual neurons. Retinal luminance adaption begins at the photoreceptor level whereas retinal contrast adaption is believed to start at later stages of processing as cones have been reported not to adapt to contrast. However, we find that this might not be entirely the case.
Light responses of cone photoreceptors from isolated gold fish retina were recorded by whole cell voltage and current clamp techniques. Both naturalistic chromatic time series of intensities and monochromatic artificial time series of intensities were used. Different contrast levels were generated by using different modulation depths with equal mean luminance. Transfer functions were derived.
When analysing the overall response amplitudes of cones in voltage clamp conditions the shape of the transfer function does not change. However, in current clamp cones attenuated higher frequency components of the lower contrast stimuli to a greater extent than they did for the higher contrast stimuli indicating that cones shift their bandwidth depending on the contrast of the stimulus.
Cones adapt to different contrast conditions not by scaling their response amplitudes but by altering their frequency bandwidth. The difference between current and voltage clamp recording indicates that this process is mediated by cone membrane properties and not the phototransduction cascade. Such an adaptive filtering system is consistent with van Hateren’s (1992) proposed adaptive filter employed to maximise sensory information in different signal to noise ratio conditions.
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