The coding of uniform colour figures in monkey visual cortex (original) (raw)
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The spatial transformation of color in the primary visual cortex of the macaque monkey
nature neuroscience, 2001
Perceptually, color is used to discriminate objects by hue and to identify color boundaries. The primate retina and the lateral geniculate nucleus (LGN) have cell populations sensitive to color modulation, but the role of the primary visual cortex (V1) in color signal processing is uncertain. We reevaluated color processing in V1 by studying single-neuron responses to luminance and to equiluminant color patterns equated for cone contrast.
Color in the Cortex: single- and double-opponent cells
Vision Research, 2011
This is a review of the research during the past 25 years on cortical processing of color signals. At the beginning of the period the modular view of cortical processing predominated. However, at present an alternative view, that color and form are linked inextricably in visual cortical processing, is more persuasive than it seemed in 1985. Also, the role of the primary visual cortex, V1, in color processing now seems much larger than it did in 1985. The re-evaluation of the important role of V1 in color vision was caused in part by investigations of human V1 responses to color, measured with functional magnetic resonance imaging, fMRI, and in part by the results of numerous studies of single-unit neurophysiology in non-human primates. The neurophysiological results have highlighted the importance of double-opponent cells in V1. Another new concept is population coding of hue, saturation, and brightness in cortical neuronal population activity.
A contrast and surface code explains complex responses to black and white stimuli in V1
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2014
We investigated the cortical mechanisms underlying the visual perception of luminance-defined surfaces and the preference for black over white stimuli in the macaque primary visual cortex, V1. We measured V1 population responses with voltage-sensitive dye imaging in fixating monkeys that were presented with white or black squares of equal contrast around a mid-gray. Regions corresponding to the squares' edges exhibited higher activity than those corresponding to the center. Responses to black were higher than to white, surprisingly to a much greater extent in the representation of the square's center. Additionally, the square-evoked activation patterns exhibited spatial modulations along the edges and corners. A model comprised of neural mechanisms that compute local contrast, local luminance temporal modulations in the black and white directions, and cortical center-surround interactions, could explain the observed population activity patterns in detail. The model captured ...
The Impact of Suppressive Surrounds on Chromatic Properties of Cortical Neurons
Journal of Neuroscience, 2004
Stimulation of the suppressive surround of a cortical neuron affects the responsivity and tuning of the classical receptive field (CRF) on several stimulus dimensions. In V1 and V2 of macaques prepared for acute electrophysiological experiments, we explored the chromatic sensitivity of the surround and its influence on the chromatic tuning of the CRF. We studied receptive fields of single neurons with patches of drifting grating of optimal spatial frequency and orientation and variable size, modulated along achromatic or isoluminant color directions. The responses of most neurons declined as the patch was enlarged beyond the optimal size (surround suppression). In V1 the suppression evoked by isoluminant gratings was less than one-half that evoked by achromatic gratings. Consequently, many cells were most sensitive to achromatic modulation when patches just covered the CRF but were most sensitive to isoluminant modulation when patches were enlarged to cover the suppressive surround. Non-oriented neurons that were strongly chromatically opponent generally lacked suppressive surrounds. In V2 most neurons showed equal surround suppression from isoluminant gratings and achromatic gratings. This makes the relative sensitivity of V2 neurons to achromatic and isoluminant gratings mainly independent of the size of the grating. We also measured the chromatic properties of the CRF in the presence of differently colored surrounds. In neither V1 nor V2 did the surround alter the chromatic tuning of the CRF. Cortical mechanisms sensitive to chromatic contrast seem to provide little input to the suppressive surrounds of V1 neurons but substantial input to those of V2 neurons.
Psychophysical Chromatic Mechanisms in Macaque Monkey
Journal of Neuroscience, 2012
Chromatic mechanisms have been studied extensively with psychophysical techniques in humans, but the number and nature of the mechanisms are still controversial. Appeals to monkey neurophysiology are often used to sort out the competing claims and to test hypotheses arising from the experiments in humans, but psychophysical chromatic mechanisms have never been assessed in monkeys. Here we address this issue by measuring color-detection thresholds in monkeys before and after chromatic adaptation, employing a standard approach used to determine chromatic mechanisms in humans. We conducted separate experiments using adaptation configured as either flickering full-field colors or heterochromatic gratings. Full-field colors would favor activity within the visual system at or before the arrival of retinal signals to V1, before the spatialtransformationofcolorsignalsbythecortex.Conversely,gratingswouldfavoractivitywithinthecortexwhereneuronsareoftensensitive tospatialchromaticstructure.Detectionthresholdswereselectivelyelevatedforthecolorsoffull-fieldadaptationwhenitmodulatedalongeither of the two cardinal chromatic axes that define cone-opponent color space [L vs M or S vs (L ϩ M)], providing evidence for two privileged cardinal chromatic mechanisms implemented early in the visual-processing hierarchy. Adaptation with gratings produced elevated thresholds for colors of the adaptation regardless of its chromatic makeup, suggesting a cortical representation comprised of multiple higher-order mechanisms each selective for a different direction in color space. The results suggest that color is represented by two cardinal channels early in the processing hierarchy and many chromatic channels in brain regions closer to perceptual readout.
Colour coding in rhesus monkey prestriate cortex
Brain Research, 1973
One of the striking features of the anatomical organisation of the prestriate cortex in the monkey is the mosaic of sub-areas into which it may be divided on the basis of the afferent input, efferent output and inter-hemispheric connections of its individual partsl, 5-s. Such a mosaic organisation no doubt reflects a functional division of labour within the prestriate cortex for handling the various parameters of vision, the emphasis on any particular function in any particular area being presumably dictated by the organisation of the afferent input to that area. The topographically organised point-to-point input from the lateral geniculate nucleus to area 17 is reflected functionally in the detailed region-by-region form analysis that this area performs 4. On the other hand, the overlapping, convergent input from area 17 to the cortex of the posterior bank of the superior temporal sulcus is reflected functionally in the generalisation for receptive field position and the emergence of movement as a critical stimulus parameter 2. In this paper, we report briefly the response properties of units to simple visual stimulation in another prestriate area, the fourth visual area (V4) which we have already defined anatomically 7. This area lies in the anterior bank of the lunate sulcus dorsally and, because of the complicated gyral changes, emerges ventrally in the posterior bank of the inferior occipital sulcus 7. It receives an input from areas 18 and 19 but this projection does not appear to be very precisely defined topographically. We have recorded from 77 single units in this area, in 8 monkeys, using tungsten-inglass microelectrodes, and in every case the units have been cotour coded, responding vigorously to one wavelength and grudgingly, or not at all, to other wavelengths or to white light at different intensities. The animals were anaesthetised with sodium pentobarbital and paralysed with gallamine triethiodide (5 mg/kg/h). A hole was drilled in the skull over the appropriate
eneuro, 2016
The lateral geniculate nucleus is thought to represent color using two populations of cone-opponent neurons [L vs M; S vs (L ϩ M)], which establish the cardinal directions in color space (reddish vs cyan; lavender vs lime). How is this representation transformed to bring about color perception? Prior work implicates populations of glob cells in posterior inferior temporal cortex (PIT; the V4 complex), but the correspondence between the neural representation of color in PIT/V4 complex and the organization of perceptual color space is unclear. We compared color-tuning data for populations of glob cells and interglob cells to predictions obtained using models that varied in the color-tuning narrowness of the cells, and the color preference distribution across the populations. Glob cells were best accounted for by simulated neurons that have nonlinear (narrow) tuning and, as a population, represent a color space designed to be perceptually uniform (CIELUV). Multidimensional scaling and representational similarity analyses showed that the color space representations in both glob and interglob populations were correlated with the organization of CIELUV space, but glob cells showed a stronger correlation. Hue could be classified invariant to luminance with high accuracy given glob responses and above-chance accuracy given interglob responses. Luminance could be read out invariant to changes in hue in both populations, but interglob cells tended to prefer stimuli having luminance contrast, regardless of hue, whereas glob cells typically retained hue tuning as luminance contrast was modulated. The combined luminance/hue sensitivity of glob cells is predicted for neurons that can distinguish two colors of the same hue at different luminance levels (orange/brown).