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Sherry X. Xian, Tirin Moore; Contextual influences on the chromatic properties of macaque V4 neurons. Journal of Vision 2006;6(6):688. doi: 10.1167/6.6.688.
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We recently found that a large proportion of V4 neurons are highly selective to cone isolating stimuli. Most color selective V4 neurons respond best to a narrow range of chromaticities in color space, and thus these neurons indeed seem to play a role in color perception. V4 neurons also have large, suppressive non-classical receptive field surrounds (Schein & Desimone, 1990). Here we examine how contextual influences from complex backgrounds modulate responses of V4 neurons and how these modulations correspond to perceptual measurements of color appearance changes caused by local induction and induction from grouping (Xian & Shevell, 2005).
The experiments were carried out in two alert, fixating monkeys. Stimuli were chromatic, oriented bars (1°×0.25°, 25cd/m2) presented on a complex and variable background (16° diameter, 15cd/m2) and centered on the receptive field (RF) of individual V4 neurons. Each bar had different L- or S-cone contrasts relative to equal energy spectrum and the luminance of all bar colors was held constant. A minimum motion technique was used to determine equiluminance for each monkey using the method of Logothetis and Charles (1990). During each experimental trial, monkeys fixated a central point to receive a juice reward. Once the monkey began fixating, a pseudo-random sequence of 5–11 colors was presented. Each bar stimulus lasted 100–250 msec and was followed by 50 msec of background.
We found that the chromatic tuning of V4 neurons could be significantly altered by changes in chromatic context, and in ways consistent with perceptual observations from human psychophysical experiments.
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