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Chun-I Yeh, Dajun Xing, Robert M. Shapley; ‘Black’ dominance measured with different stimulus ensembles in macaque primary visual cortex V1. Journal of Vision 2010;10(7):939. doi: 10.1167/10.7.939.
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© ARVO (1962-2015); The Authors (2016-present)
Most neurons in layer 2/3 (not layer 4c) of V1 have stronger responses to ‘black’ (negative contrast) than to ‘white’ (positive contrast) when measured by reverse correlation with sparse noise (Jones and Palmer 1987). Furthermore, the degree of the black dominance in V1 depends on the stimulus ensemble – the black dominance is much stronger when neuronal responses are measured with sparse noise than with Hartley stimuli (Ringach et al 1997). Sparse and Hartley stimuli differ in many ways. First, the individual stimulus size of sparse noise is much smaller than that of Hartley stimuli. Second, the dark and bright pixels of sparse noise are present separately in time while those of Hartley stimuli are shown simultaneously. Third, there are spatial correlations along the long axis of Hartley stimuli that are not present in sparse noise. Which of these differences might contribute to the disparity in black dominance? Here we introduced a third stimulus ensemble – a binary checkerboard white noise (m-sequence, Reid et al 1997) to measure the black-dominant responses in sufentanil-anesthetized monkey V1. Both white noise and Hartley stimuli activate a larger population of neurons than sparse noise, and dark and bright pixels appear simultaneously under both conditions. Unlike Hartley stimuli, neighboring pixels of white noise are uncorrelated. Among the V1 neurons with significant responses (signal-to-noise ratio>1.5) to all three ensembles, black-dominant neurons (BDNs) largely outnumbered white-dominant neurons in output layer 2/3 with all three stimulus ensembles (% of BDNs: 76~82%) while the numbers of black and white-dominant neurons were nearly equal in input layer 4c (% of BDNs: 40~60%). The degree of the black-dominant response was significantly stronger for white noise than for Hartley stimuli (p<0.02, Wilcoxon signed rank test). These results indicate that the degree of black dominance depends on the spatial structure of the stimulus ensemble.
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