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Joshua M. Kunken, Hao Sun, Barry B. Lee; Modeling macaque ganglion cell response in studies of light adaptation using the Westheimer paradigm. Journal of Vision 2004;4(8):226. doi: 10.1167/4.8.226.
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© ARVO (1962-2015); The Authors (2016-present)
Ganglion cell responses to a sinusoidal stimulus with a pedestal of variable size simulating the Westheimer paradigm were obtained via in vivo extracellular recording from macaque retinal ganglion cells. Data were compared to results obtained psychophysically using the same stimulus. On-center magnocellular cell response gradually decreased as pedestal area increased, until a plateau was reached with little recovery, compatible with operation of a local adaptation pool. Off-center cells demonstrated a vigorous response with small pedestals, but as size increased, responsivity decreased dramatically and subsequently recovered as pedestals encroached into the surround. Data from on-center cells were fitted with a feedforward gain control model designed to simulate the effect of an adaptation pool on cell responses. Adaptation pool size was found to be about the size of a ganglion cell receptive field center. Due to the drop in response at intermediate pedestal size, which appeared to be due to an ‘iceberg’ effect due to abolition of maintained firing, the model could not completely fit off-center cell response profiles, but did capture the initial decrease and final recovery level in response at small and large pedestal sizes, respectively. These results, and the comparison with psychophysics, suggest that a complex physiological substrate is most likely responsible for the classical Westheimer curve, involving an interaction between local adaptation pools in the retina and changes in maintained firing rate due to center-surround receptive field mechanisms, followed by a cortical component.
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