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Andrew J. Zele, Dingcai Cao, Joel Pokorny; Dark-adapted rods alter cone temporal impulse response functions. Journal of Vision 2006;6(13):68. doi: 10.1167/6.13.68.
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Purpose: Dark-adapted rods in the area surrounding a luminance-modulated field suppress flicker detection (e.g. Cao, Zele & Pokorny, 2006; Goldberg, Frumkes & Nygaard, 1983). Here we consider whether rod mediated suppression is due to a change in the cone impulse response function (IRF) or due to temporal modulation per se.
Methods: A 2-channel, 4-primary photostimulator provided control of cone stimulation. Periodic temporal contrast sensitivity functions (TCSF) and 2-pulse summation data were determined for 80 Td luminance stimuli (2∞ field; 7.5° eccentricity). Measurements were made under three conditions, with an 80 Td 13° surround, with a dark-surround following 30 min of dark adaptation, or with a dark surround during the cone-plateau after recovery from a bleach (∼52%). Cone IRFs were derived from TCSFs using the Stork & Falk (1987) method or directly from 2-pulse data using the Burr & Marrone (1993) method.
Results: For each of the three conditions, the two methods generated similar IRF estimates. IRFs for the 80 Td surround condition had the largest amplitudes. For the dark surround, amplitudes of the IRFs were smaller following dark adaptation than following the bleach.
Conclusions: Dark-adapted rods in the surround area reduce cone IRF amplitudes, derived from both periodic and pulsed luminance stimuli. Rod suppression of cone function is not due to temporal modulation per se. This suppression may have consequences in real world situations where objects or persons are viewed in dim light conditions.
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