| Gegenfurtner, K.R. Cortical mechanisms of colour vision Nature reviews 2003 (4):563-572 [pdf] |
| The perception of colour is a central component of primate vision. Colour facilitates object perception and recognition, and has an important role in scene segmentation and visual memory. Moreover, it provides an aesthetic component to visual experiences that is fundamental to our perception of the world. Despite the long history of colour vision studies, much has still to be learned about the physiological basis of colour perception. Recent advances in our understanding of the early processing in the retina and thalamus have enabled us to take a fresh look at cortical processing of colour. These studies are beginning to indicate that colour is processed not in isolation, but together with information about luminance and visual form, by the same neural circuits, to achieve a unitary and robust representation of the visual world. |
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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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| Yamauchi, Y. & al What determines unique yellow, L/M cone ratio or visual experience ? 9th Congress of the International Colour Association 2002 (4421):275-278 [pdf] |
| Unique yellow is considered to represent the equilibrium point of the red-green opponent chromatic mechanism. There are several hypotheses that attempt to explain how this equilibrium point is established. The determinant for unique yellow, however, has not yet been clarified. Here we explored whether the L/M cone ratio or visual information determines unique yellow. If the former is the case, we expect that subjects with large differences in their L/M cone ratio would set different spectral lights to appear as unique yellow. The results of such an experiment, however, did not show a substantial difference in the value of unique yellow for two subjects with very different cone ratios. On the other hand, if the latter is the case, unique yellow should change when altering the chromaticity of the surrounding visual environment. To test this hypothesis, we conducted long-term adaptation experiments, in which subjects spent 8 to 12 hours in a chromatically altered environment. A significant shift of unique yellow was observed after spending time in such an environment for several days. These results indicate that the red-green opponent channel includes a plastic normalization mechanism that adjusts its balance point based on visual experience. |
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