| Buchsbaum, G., Bloch, O. Color categories revealed by non-negative matrix factorization of Munsell color spectra Vision Research 2002 (42):559-563 [html] |
| Non-negative matrix factorization (NMF, Nature 401 (1999) ) is a method to derive non-negative basis functions for sets of data that are inherently non-negative, such as color spectra. We applied NMF to Munsell color spectra and investigated the color names associated with the non-negative basis functions. NMF yields basis functions compatible with established color naming categories. |
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| De Valois, R.L., De Valois, K.K., Switkes, E., Mahon, L. Hue scaling of isoluminant and cone-specific lights Vision Research 1997 (37)7:885-97 [html] |
| ing a hue scaling technique, we have examined the appearance of colored spots produced by shifts from white to isoluminant stimuli along various color vectors in order to examine color appearance without the complications of the combined luminance and chromatic stimulation involved in most previous hue scaling studies, which have used flashes of monochromatic light. We also used spots lying along cone-isolating vectors in order to determine what hues would be reported with a change in activation of only single cone types or of only single geniculate opponent-cell types, an issue of direct relevance to any model of color vision. We find that: 1. Unique hues do not correspond either to the change in activation of single cone types or of single geniculate opponent-cell types. This is well known to be the case for yellow and blue, but we find it to be true for red and green as well. 2. These conclusions are not limited to the particular white (Illuminant C) used as an adapting background in most of the experiments. Shifts along the same cone-contrast vectors relative to different backgrounds lead to much the same hue percepts, independent of the starting white used. 3. The shifts of the perceptual colors from the geniculate axes are in the directions, and close to the absolute amounts, predicted by our [De Valois & De Valois (1993). Vision Research, 33, 1053-1065] multi-stage color model in which we postulate that the S-opponent cells are added to or subtracted from the M- and L-opponent cells to form the four perceptual color systems. 4. There are distinct asymmetries with respect to the extent to which various hues within each perceptual opponent system deviate from the geniculate opponent-cell axes. Blue is shifted more from the S-LM axis than is yellow; green is shifted more from the L-M axis than is red. There are also asymmetries in the angular extent of opponent color regions. Blue is seen over a larger range of color vectors than is yellow, and red over a slightly larger range than green. 5. Such asymmetries are not accounted for by any model that treats red-green and yellow-blue each as unitary, mirror-image opponent-color systems. Although red and green are perceptually opponent, the red and green perceptual systems do not appear to be constructed in a mirror-image fashion with respect to input from different cone types or from different geniculate opponent-cell types. The same is true for yellow and blue. |
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| Maloney, L.T. Illuminant cues in surface color perception: tests of three candidate cues Vision Research 2001 (41):2581-2600 [pdf] |
| Many recent computational models of surface color perception presuppose information about illumination in scenes. The models differ primarily in the physical process each makes use of as a cue to the illuminant. We evaluated whether the human visual system makes use of any of three of the following candidate illuminant cues: (1) specular highlight, (2) full surface specularity [Lee, H. C. (1986). Method for computing the scene-illuminant chromaticity from specular highlights. Journal of the Optical Society of America A, 3(10), 1694 1699; D Zmura, M., & Lennie, P. (1986). Mechanisms of color constancy. Journal of the Optical Society of America A, 3(10), 1662 1672], and (3) uniform background. Observers viewed simulated scenes binocularly in a computer-controlled Wheatstone stereoscope. All simulated scenes contained a uniform background plane perpendicular to the observer s line of sight and a small number of specular, colored spheres resting on the uniform background. Scenes were rendered under either standard illuminant D65 or standard illuminant A. Observers adjusted the color of a small, simulated test patch to appear achromatic. In a series of experiments we perturbed the illuminant color signaled by each candidate cue and looked for an influence of the changed cue on achromatic settings. We found that the specular highlight cue had a significant influence, but that the influence was asymmetric: greater when the base illuminant, CIE standard Illuminant A, was perturbed in the direction of Illuminant D65 than vice versa. Neither the full surface specularity cue nor the background cue had any observable influence. The lack of influence of the background cue is likely due to the placement of the test patch in front of the background rather than, as is typical, embedded in the background |
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| Teller, D.Y. Spatial and temporal aspects of infant color vision Vision Research 1998 (38):3275-3282 [html] |
| The present paper constitutes a review of the literature on young infants' chromatic discrimination capabilities. A series of early studies showed that infants as young as two months postnatal can make at least some chromatic discriminations between stationary, homogeneous fields of different wavelength compositions. Current studies of spatial and temporal contrast sensitivity functions (CSFs) for red/green isoluminant stimuli suggest that spatial chromatic CSFs show developmental changes in sensitivity and spatial scale, but not curve shape; while temporal chromatic CSFs (tCSFs) show developmental changes in sensitivity and curve shape, but not temporal scale. Infants can also code the direction of motion of moving isoluminant red/green gratings, for both continuous and quadrature motion. The possible mechanisms that underlie infants' chromatic discriminations are discussed. |
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| Goebel, R. & al Sustained extrastriate cortical activation without visual awareness revealed by fMRI studies of hemianopic patients Vision Research 2001 (3):1459-74 [html] |
| Patients with lesions in the primary visual cortex (V1) may show processing of visual stimuli presented in their field of cortical blindness even when they report being unaware of the stimuli. To elucidate the neuroanatomical basis of their residual visual functions, we used functional magnetic resonance imaging in two hemianopic patients, FS and GY. In the first experiment, a rotating spiral stimulus was used to assess the responsiveness of dorsal stream areas. Although no response was detectable within denervated or destroyed early visual cortex, motion-sensitive areas (hMT+/V5) ipsilateral to the lesion showed a strong sustained hemodynamic response. In GY, this activation was at least as strong as that of his contralesional hMT+/V5 to the stimulus in the normal hemifield. In the second experiment, coloured images of natural objects were used to assess the responsiveness of ventral stream areas. Again, no activity was detectable in ipsilesional early visual areas, but extrastriate areas in the lateral occipital cortex (hMT+/V5 and LO) and within the posterior fusiform gyrus (V4/V8) showed a robust sustained hemodynamic response. In both experiments, we observed that ipsilesional areas responded to stimuli presented in either hemifield, whereas the normal hemisphere responded preferentially to stimuli in the sighted hemifield. As only one subject occasionally noticed the onset of stimulation in the impaired field, the unexpectedly strong sustained activity in ipsilesional dorsal and ventral cortical areas appears to be insufficient to generate conscious vision. |
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| Bell, A.J., Sejnowski, T.J. The 'independent components' of natural scenes are edge filters Vision Research 1997 37:3327-3338 [html] |
| Field (1994) has suggested that neurons with line and edge selectivities found in primary visual cortex of cats and monkeys form a sparse, distributed representaton of natural scenes, and Barlow (1989) has reasoned that such responses should emerge from an unsupervised learning algorithm that attempts to find a factorial code of independent visual features. We show here that a new unsupervised learning algorithm that is based on information maximisation, a non-linear `infomax' network (Bell and Sejnowski, 1995) when applied to an ensemble of natural scenes, produces sets of visual filters that are localised and oriented. Some of these filters are Gabor-like and resemble those produced by the sparseness-maximisation network of Olshausen & Field (1996). In addition, the outputs of these filters are as independent as possible, since the infomax network is able to perform Independent Components Analysis (ICA). We compare the resulting ICA filters and their associated basis functions, with ... |
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| Stockman, A., Sharpe L.T., The spectral sensitivities of the middle- and long-wavelength-sensitive cones derived from measurements in observers of known genotype Vision Research 2000 (40)13:1711-37 |
| The spectral sensitivities of middle- (M-) and long- (L-) wavelength-sensitive cones have been measured in dichromats of known genotype: M-cone sensitivities in nine protanopes, and L-cone sensitivities in 20 deuteranopes. We have used these dichromat cone spectral sensitivities, along with new luminous efficiency determinations, and existing spectral sensitivity and color matching data from normal trichromats, to derive estimates of the human M- and L-cone spectral sensitivities for 2 and 10 degrees dia. central targets, and an estimate of the photopic luminosity function [V(lambda)] for 2 degrees dia. targets, which we refer to as V(2)*(lambda). These new estimates are consistent with dichromatic and trichromatic spectral sensitivities and color matches. |
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| Chichilisky, E., Wandell, B.A. Trichromatic opponent color classification Vision Research 1999 [pdf] |
| Stimuli varying in intensity and chromaticity, presented on numerous backgrounds, were classified into red/green, blue/yellow and white/black opponent color categories. These measurements revealed the shapes of the boundaries that separate opponent colors in three-dimensional color space. Opponent color classification boundaries were generally not planar, but their shapes could be summarized by a piecewise linear model in which increment and decrement color signals are combined with different weights at two stages to produce opponent color sensations. The effect of background light on classification was largely explained by separate gain changes in increment and decrement cone signals. |
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| Valberg, A. Unique hues: an old problem for a new generation Vision Research 2001 (41):1645-1657 [html] |
| The practical success of the classical theories of colour vision, such as that of Young-Helmholtz when applied to the measurement and reproduction of colour stimuli, and that of Hering's in art and architecture, has overshadowed the fact that neither theory achieved its main goal, namely to explain colour qualities. Neither the three types of cone, nor the first opponent stages of neural processing in the retina and the lateral geniculate nucleus can serve as direct correlates to the perception of elementary, or unique colours, such as red, green, yellow and blue. While our subjective experiences of these qualities do not submit to measurement, physiological conditions that are required to perceive colours of a constant hue can be identified. For instance, a constant ratio of responses of different types of opponent cells in the retina and the lateral geniculate nucleus of primates may serve as a neurophysiological correlate of a constant hue. This is, however, not the correlate for seeing a particular hue quality, say unique red. This latter correlate, if it exists as a separable entity, must be associated with yet unidentified, higher-level neural activities. The fundamental problems encountered in relating colour qualities to neural activities are discussed and references are made to the current debate about phenomenal consciousness. |
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| Buchsbaum, G., Bloch, O. Color categories revealed by non-negative matrix factorization of Munsell color spectra Vision Research 2002 (42):559-563 |
| De Valois, R.L., De Valois, K.K., Switkes, E., Mahon, L. Hue scaling of isoluminant and cone-specific lights Vision Research 1997 (37)7:885-97 |
| Maloney, L.T. Illuminant cues in surface color perception: tests of three candidate cues Vision Research 2001 (41):2581-2600 |
| Teller, D.Y. Spatial and temporal aspects of infant color vision Vision Research 1998 (38):3275-3282 |
| Goebel, R. & al Sustained extrastriate cortical activation without visual awareness revealed by fMRI studies of hemianopic patients Vision Research 2001 (3):1459-74 |
| Bell, A.J., Sejnowski, T.J. The 'independent components' of natural scenes are edge filters Vision Research 1997 37:3327-3338 |
| Stockman, A., Sharpe L.T., The spectral sensitivities of the middle- and long-wavelength-sensitive cones derived from measurements in observers of known genotype Vision Research 2000 (40)13:1711-37 |
| Chichilisky, E., Wandell, B.A. Trichromatic opponent color classification Vision Research 1999 |
| Valberg, A. Unique hues: an old problem for a new generation Vision Research 2001 (41):1645-1657 |