Effect of Background Colors on the Tuning of Color-Selective Cells in Monkey Area V4

Abstract

. When objects are viewed in different illuminants, their color does not change or changes little in spite of significant changes in the wavelength composition of the light reflected from them. In previous studies, we have addressed the physiology underlying this color constancy by recording from cells in areas V1, V2, and V4 of the anesthetized monkey. Truly color-coded cells, ones that respond to a patch of a given color irrespective of the wavelength composition of the light reflected from it, were only found in area V4. In the present study, we have used a different approach to test the responses of V4 cells in both anesthetized and awake behaving monkeys. Stimuli of different colors, embedded within a Mondriantype multicolored background, were used to identify the chromatic selectivity of neurons. The illumination of the background was then varied, and the tuning of V4 neurons was tested again for each background illumination. With anesthetized monkeys, the psychophysical effect of changing background illumination was inferred from our own experience, whereas in the awake behaving animal, it was directly reported by the monkey. We found that the majority of V4 neurons shifted their color-tuning profile with each change in the background illumination: each time the color of the background on the computer screen was changed so as to simulate a change in illumination, cells shifted their color-tuning function in the direction of the chromaticity component that had been increased. A similar shift was also observed in colored match-to-sample psychometric functions of both human and monkey. The shift in monkey psychometric functions was quantitatively equivalent to the shift in the responses of the corresponding population of cells. We conclude that neurons in area V4 exhibit the property of color constancy and that their response properties are thus able to reflect color perception. I N T R O D U C T I O NPerhaps the most striking characteristic of the organization of the visual cortex is its functional specialization, by which we mean that different attributes of the visual scene, among them color, are processed by anatomically separate and functionally specialized systems (Livingstone and Hubel 1988;Zeki 1978;Zeki et al. 1991). Functional specialization is also reflected in the temporal perceptual dimension because different attributes of the visual scene are perceived asynchronously, color being perceived before motion and form (Arnold et al. 2001; Moutoussis and Zeki 1997a,b). The notion of a cortical specialization for color should in fact have been hinted at before these discoveries, through the clinical studies of a patient with acquired color vision defects after lesions in the lingual and fusiform gyri (Verrey 1888). But this evidence was rapidly dismissed by Salomon Henschen and by Gordon Holmes (see Zeki 1990 for a review) because Verrey, without explicitly saying so, had implied that the primary visual receptive center in the brain was not restricted to the calcarine (striate) cortex, as supposed by...

Dissociable Effects of Natural Image Structure and Color on LFP and Spiking Activity in the Lateral Prefrontal Cortex and Extrastriate Visual Area V4

“…Accordingly, we did not find significant stimulus correlations between VEPs and spiking activity. The lack of color sensitivity at the population level in V4 seems to be at odds with previous studies recording single unit activity that illustrate the importance of V4 in color processing (Zeki, 1980(Zeki, , 1983aWild et al, 1985;Walsh et al, 1993;Kusunoki et al, 2006;Stoughton and Conway, 2008;Conway and Tsao, 2009). Instead, our findings might rather be consistent with studies questioning a specific role of V4 neurons in color processing (Schein et al, 1982;Tootell et al, 2004).…”

Shape encoding consistency across colors in primate V4

“…Past studies in area V4 have demonstrated selectivity for both stimulus form (Desimone and Schein 1987;Gallant et al 1993;Kobatake and Tanaka 1994;Connor 1999, 2001) and color (Bushnell et al 2011b;Conway et al 2007;Kotake et al 2009;Kusunoki et al 2006;Schein and Desimone 1990;Zeki 1973). However, because characterizations of tuning have typically been performed along the dimension of interest (shape or color) while holding the other (color or shape) constant, past V4 results do not reveal whether selectivity for form and color interact at the single-neuron level, i.e., whether shape preferences are the same regardless of the color of the stimulus.…”

Perceptual Color Map in Macaque Visual Area V4

“…Furthermore, the color map may incorporate knowledge or qualities that are intrinsic constructs, such as color constancy (Schein and Desimone, 1990), the percept of which cannot be simply predicted from the physical properties of the light (McCann et al, 1976;Land, 1977;Lotto and Purves, 2002;Kusunoki et al, 2006). Thus, some aspects of its recorded activity may not only represent colors in the external world but also reflect correlations to internal factors, arising from the complex dynamics of the underlying cortical circuits (Harris, 2005).…”