Contribution of different lateral geniculate cell types to visual behavior

Acquisition of color opponent representation by a three-layered neural network model

This paper discusses color representation in the visual system by analysis of a three-layered neural network model. The model incorporates physiological knowledge of color representation at the sensor level (broad-band trichromatic representation by cones) and the higher level (narrow-band color representation by color-coded cells in V4). We trained the model to perform a mapping between these color representations by the back propagation algorithm and analyzed the acquired characteristics of the hidden units. It turned out that the hidden units learned characteristics similar to those of the color opponent cells found in the visual system. It was concluded that the R-G and Y-B color opponent representations reflect the efficiency of the color representation in the visual system from investigations on the efficiency of color representation in the hidden layer and on the capability of the color recognition task of the model.

Effects of patterned backgrounds on responses of lateral geniculate neurons in cat

In the lateral geniculate nucleus (LGN) of paralyzed cats under urethane anaesthesia, an extensive disinhibitory region (DIR) outside the inhibitory surround of the receptive field (RF) was found in both sustained and transient cells. Its extent is comparable to that of McIlwain's periphery effect (1964). The responses to a light spot, flashed into different parts of the RF center, were used to assess the effect of different background patterns, located over the DIR, on responsiveness and receptive field organization. A straight line background cutting across the RF center led to a marked shrinkage in RF size and to a suppression of the center response. In sustained cells, these influences were not due to the light flux of the background, but were mainly due to the spatial property of the line itself. This was demonstrated by comparing the effect of a straight line background with that of a zigzag line or of distributed dots. The light flux for the different patterns and their spatial weighting was the same, so that they differed from each other solely in their form. A straight line background elicited much stronger suppression of the center response and more marked shrinkage of the RF than if the component dots are dispersed over a wider area, but keeping the radial distances of the individual dots from the RF-center constant. The data suggest that the dispersion of the component dots in different backgrounds plays an important role as response amplitude and RF diameter increase proportional to the dispersive area of the background patterns. For transient cells, all backgrounds used showed similar effects on center responses and RF diameter, indicating that for them it was the light flux of the backgrounds rather than their spatial property that caused the effects.

Early color deprivation and subsequent color vision in a dichromatic monkey

A squirrel monkey (Saimiri sciureus) was reared for the first 4 months of life in a dim, colorless environment. Following an additional 10 months of normal visual experience, tests of color vision and spectral sensitivity were run on this animal and a control subject. The results suggest that the adult expression of dichromatic color vision does not depend on color experience during the first 4 months of life.

Colour-spatial vision

A critical survey is made of neurophysiological and psychophysiological investigations of colour vision. A neuronal model of colour-spatial vision is suggested. The model allows a unified explanation of the whole range of psychophysiological phenomena: the mixing of colours of high-frequency image components, the McCollough type colour after-effects, the simultaneous and successive colour contrast, the hue constancy perception, the appearance of non-spectral colours by mixing of monochromatic lights. A suggestion is made as to the existence of two main mechanisms of colour vision. The first of these, by means of Fourier transforms, gives a set of coefficients which describes the spatial distribution of light (quantity of energy) and hue (quality of energy) in the visual field. The second mechanism establishes colour names in each chromatically homogenous area of the field described by the first mechanism. Both mechanisms cooperate on the basis of their common spatial organization.