A psychophysical dissection of the brain sites involved in color-generating comparisons

Moutoussis, Konstantinos; Zeki, Semir

doi:10.1073/pnas.110570897

Cited by 19 publications

(15 citation statements)

References 35 publications

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“…On the other hand, the fact that neurons modulate their chromatic responses with extra-classical receptive-field changes as early as V1 and LGN suggests that color-constancy relevant computations are initiated much earlier in the system than area V4. This has been also clearly demonstrated psychophysically, by dichoptically separating the "target" from the "surround" and showing that, in this case, there is a total failure of any spatial interactions between the two (Moutoussis and Zeki 2000). We therefore believe that, although spatial chromatic interactions begin to take place very early in the visual system, the generation of color per se is a property of higher visual areas of the brain.…”

Section: Role Of V4 In Color Perceptionmentioning

confidence: 86%

“…Whatever the implementation strategy may be, it must involve a comparison of the amounts of long-, middle-, and short-wave light reflected from one surface and from surrounding surfaces (Land 1974;Land and McCann 1971). Psychophysical, imaging and electrophysiological evidence suggests that such a comparison is shared between early and late stages of the visual pathway (Bartels and Zeki 2000;Moutoussis and Zeki 2000). Physiological evidence shows that cells whose responses correlate with color as perceived by humans, rather than the wavelength composition of the stimulus, occur in area V4 but not V1 (Zeki 1983; but see also Wachtler et al 2003 and DISCUSSION).…”

Section: Introductionmentioning

confidence: 99%

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

Kusunoki

Moutoussis²,

Zeki³

2006

Journal of Neurophysiology

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. 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...

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Section: Role Of V4 In Color Perceptionmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 99%

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

Kusunoki

Moutoussis²,

Zeki³

2006

Journal of Neurophysiology

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“…A possible strategy by which the brain achieves this is to compare the different amounts of long-, middle-, and short-wave light across space (Land 1974;Land and McCann 1971). Recent psychophysical and imaging evidence suggests that such a comparison is shared between early and late stages of the visual pathway (Bartels and Zeki 2000;Moutoussis and Zeki 2000). On the other hand, physiological evidence shows that cells whose responses correlate with color as perceived by humans, rather than the wavelength composition of the stimulus, occur in area V4 but not V1 (Zeki 1983a): striate cortex (and some V4) cells were found to respond to an area of any color in the scene, as long as it is made to reflect a sufficient minimum amount of light of their preferred wavelength and lesser amounts of the other two wavelengths.…”

Section: Introductionmentioning

confidence: 99%

Responses of Spectrally Selective Cells in Macaque Area V2 to Wavelengths and Colors

Moutoussis

Zeki

2002

Journal of Neurophysiology

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Moutoussis, K. and S. Zeki. Responses of spectrally selective cells in macaque area V2 to wavelengths and colors. J Neurophysiol 87: 2104 -2112, 2002; 10.1152/jn.00248.2001. We have recorded from wavelength-selective cells in macaque monkey visual area V2, interposed between areas V1 and V4 of the color-specialized pathway, to learn whether their responses correlate with perceived colors or are determined by the wavelength composition of light reflected from their receptive fields. All the cells we recorded from were unselective for the orientation and direction of motion of the stimulus, and all were histologically identified to be in the thin cytochrome oxidase stripes. Using multi-colored "Mondrian" scenes of the appropriate spatial configuration, areas of different color were placed in the receptive field of each cell and the entire scene illuminated by three projectors, passing long-, middle-, and short-wave light, respectively, in various combinations. Our results show that wavelength-selective cells in V2 respond to an area of any color depending on whether or not it reflects a sufficient amount of light of their preferred wavelength. In addition, the responses of a third of the cells tested were also influenced by the wavelength composition of their immediate surrounds, thus signaling the result of a local spatial comparison with respect to the amount of their preferred wavelength present. The responses of all also depended on the sequence with which their receptive fields were illuminated with light of the three different wavebands: cells were activated when there was an increase (and inhibited when there was a decrease) in the amount of their preferred wavelength with respect to the other two; the temporal route taken was therefore a determining factor, and, depending on it, cells would either respond or not to a particular combination of wavelengths. We conclude that although spatiotemporal wavelength comparisons are taking place in the color-specialized subdivisions of area V2, the determination of complete color-constant behavior at the neuronal level requires further processing, in other areas.

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“…4), and the dotted curves represent the performance for serial processing; both curves are optimized for best fit at low n. Other details as for Fig. 2. early in the visual pathway, perhaps within the eye itself (49,50), but as illuminant changes can be discriminated moderately well from spectral-reflectance changes with dichoptically viewed images, cone-excitation ratios might also be computed more centrally, as part of a multistage analysis of surface color (27,51,52). They cannot, of course, account completely for color constancy, which requires a spectral reference to anchor coneratio information (53,54).…”

Section: Discussionmentioning

confidence: 99%

Parallel detection of violations of color constancy

Foster

Nascimento

Amano

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

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The perceived colors of reflecting surfaces generally remain stable despite changes in the spectrum of the illuminating light. This color constancy can be measured operationally by asking observers to distinguish illuminant changes on a scene from changes in the reflecting properties of the surfaces comprising it. It is shown here that during fast illuminant changes, simultaneous changes in spectral reflectance of one or more surfaces in an array of other surfaces can be readily detected almost independent of the numbers of surfaces, suggesting a preattentive, spatially parallel process. This process, which is perfect over a spatial window delimited by the anatomical fovea, may form an early input to a multistage analysis of surface color, providing the visual system with information about a rapidly changing world in advance of the generation of a more elaborate and stable perceptual representation.parallel processing ͉ cone-excitation ratios ͉ surface color ͉ transient chromatic signals

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A psychophysical dissection of the brain sites involved in color-generating comparisons

Cited by 19 publications

References 35 publications

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

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

Responses of Spectrally Selective Cells in Macaque Area V2 to Wavelengths and Colors

Parallel detection of violations of color constancy

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