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Eduardo C Solessio, Yumiko Umino; Light adaptation and temporal contrast sensitivity in mouse. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):990.
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© ARVO (1962-2015); The Authors (2016-present)
Although the cellular mechanisms that contribute to computation of temporal contrast continue to be dissected, it remains obscure how those mechanisms translate to overall visual performance. In order to dissect these mechanisms, we have developed a novel operant conditioning assay that allows determination of temporal contrast sensitivity (TCS) functions in behaving mice.
In these operant studies, each mouse is maintained on a food-restriction schedule sufficient to provide necessary motivation to learn and perform the behavioral task [85% of expected body weight]. Mice are trained to perform a forced choice visual task: discriminate presence or absence of flicker in the overhead light illuminating the chamber. Following training we test daily the ability of mice to detect flickering from non-flickering light. Because the percent correct metric is prone to noise and response bias, we obtain a measure of performance independent of response bias and motivation by application of Theory of Signal Detection to estimate the sensitivity index, also known as discriminability factor, or d’. Contrast threshold is arbitrarily defined as the contrast necessary to elicit a d’ = 1, which by TSD produces 76% correct responses in alternative forced choice tasks. Contrast sensitivity is the inverse of the threshold. We measure TCS as a function of temporal frequency (1.5 - 48 Hz) in response to full-field flicker.
Our results show that TCS in mice shares many key features with TCS in humans: a) Weber adaptation, in which contrast threshold remains constant in response to low temporal frequencies and increasing background illumination, b) a shift in the shape of temporal contrast sensitivity functions from low to band pass filters (peak at ~15-20Hz) with increasing background illumination and c) increased temporal resolution (up to ~50Hz) with increasing background illumination.
Our data confirm that mouse is an appropriate model for studies of the cellular basis of TCS. Operant conditioning methods have previously been applied to test mouse vision, including absolute, spectral and spatial contrast sensitivities. To our knowledge, however, only one earlier behavioral study - using a water maze - reported temporal resolution in mice. Unfortunately, as described in detail by Nathan et al, the use of the water maze is problematical for a systematic study of TCS . Our approach provides a practical alternative.
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