Computation of Color and Brightness Differences by Rabbit Visual Cortex Neurons

Abstract

Extracellular recording of the activity of 54 neurons in the rabbit visual cortex in responses to substitutions of eight colored and eight monochromatic stimuli in pairs was studied. Stimuli were uniform flashes of light displayed on an SVGA monitor and illuminated the whole retina. The responses of phasic neurons showed an initial discharge (50-90 msec from the moment of the change in stimulus), associated with the brightness or color difference between the stimuli. These "discrimination discharges" were used to construct an 8 x 8 matrix for each neuron, showing the mean number of spikes per sec in responses to changes in different pairs of stimuli. Processing of the matrix by factor analysis identified the major factors determining the axes of the sensory space. A brightness space with only two dimensions, with darkness and brightness orthogonal axes, was seen for 30% of neurons. A four-dimensional color space was seen in 22% of neurons, with two color and two achromatic axes. The sensory space of these neurons was similar to the spaces obtained by analyzing the early components of visual evoked potentials in rabbits induced by changes in color stimuli and behavioral operant responses in conditioned reflex color differentiation. The fundamental coincidence of the sensory spaces obtained by different methods identifies the general nature of the principle of vector coding and the existence of special neuronal mechanisms for detection of color and brightness differences in the visual field.

Odour concentration affects odour identity in honeybees

“…Human colour vision, for example, works well with just three types of broadband detectors in the retina; olfaction, however, must devote much of its neural capacity to sensing thousands of potential odorant molecules and their combinations in the environment (Firestein 2001). Other sensory systems do not get intensity invariance 'for free' (vision, for example, employs a large range of optical, retinal and cortical processes to maintain its high degree of brightness invariance) (Colburn et al 2003;Escabi et al 2003;Polyansky et al 2005;Roe et al 2005). For olfaction, the cost of adhering strictly to concentration-invariant coding over a wide range of stimulus intensities may simply be too high; this may be supported by the fact that olfactory systems appear to have evolved convergently in diverse organisms (Hildebrand & Shepherd 1997;Eisthen 2002).…”

Coding of Luminance and Color Differences on Neurons in the Rabbit's Visual System

“…Summing up, it should be said that the sensory spaces of neurons in the superior colliculus revealed on the basis of the spikes' frequency in the early and late discharges were isomorphic to the spaces of neurons in other sections of the visual analyser (Polianskii, Evtikhin, & Sokolov, 2006;Polianskii, Evtikhin, Sokolov, & Alymkulov, 2007), and also to spaces obtained by other methods: on the basis of an analysis of the amplitudes of component N85 in evoked potentials in the visual cortex (Polianskii et al, 2000), and also on the basis of the probability of reactions under conditioned reflex differentials (Polianskii et al, 1998). This fact may serve as confirmation of Sokolov's hypothesis (Sokolov, 2000) on the vector coding of sensory information in the brain of animals and man.…”

The representation of colors in spherical space

“…5,19 A disadvantage is that, unlike one, two and three-dimensional spaces, a four-dimensional space is difficult to visualize. Nevertheless, by choosing the appropriate geometry and holding various parameters constant one can generate two-and three-dimensional images that aid visualization of classical relationships among chromaticity and luminance, e.g., the hue circle (Fig.…”

“…For example, a study of neuronal responses to substitutions of chromatic and achromatic luminous stimuli in the rabbit, a deuteranopic species, revealed two discrete populations of neuron involved in color discrimination. 19 Factor analyses of data from the two populations identified the major factors determining the axes of the sensory space as a ''brightness space'' of two dimensions and a ''color space'' of four dimensions. The significance of these findings was underscored by the observation that the two populations accounted for more than half of the neuronal cells in the cortical visual area from which recordings were made.…”

“…In the spherical model of color perception, 5,19 the coordinate, Q, is interpreted as reflecting the ''dark effect'' of retinal ''off-cells'' whose spontaneous activity is suppressed by lateral inhibition when light stimulates adjacent areas of the retina. 16 Off-cells accentuate border contrast at the retinal level and project to higher levels of the visual system.…”