[Visual evoked potentials in rabbit's visual cortex reflect variations in orientation and intensity of lines]

Amplitude variations of visual evoked potentials (VEP) in rabbit were studied using changes of three types of stimuli: lines with different orientations (0-90 degree) but constant in intensity, lines with different intensities but constant in orientation, and complex stimuli with different intensities and different orientations. Factor analysis of component N85 of VEP to stimuli with varying orientation and constant intensity revealed two-dimensional sensorial space of orientations. Also, the two-dimensional achromatic sensorial space was revealed for stimuli different only in intensities. In experiments with complex stimuli, two versions of stimulation were used. In the first version, four stimuli with varying orientation from 0 to 38.58 degrees were of 5 cd/m2 in intensity, the remaining four stimuli (from 51.44 to 90 degrees) were of 15 cd/m2 in intensity. In the sensorial space, stimuli with different intensities were disposed on the plane formed by the first two significant factors in the opposite quadrants, whereas within each quadrant, stimuli were arranged according to their orientation from minimum to maximum degrees. It is suggested that, in this version of stimulation, the interaction between two characteristics (intensity and orientation) took place with clear-cut dominance of the factor of intensity. In the second version of the experiments, also eight complex stimuli were used. Each stimulus was characterized by specific combination of orientation (one of the eight directions in the range from 0 to 90 degrees) and intensity (one of the eight intensities in the range from 5 to 21 cd/m2). Three or four significant factors were revealed in each test. Only the plane of intensity of sensorial space (XIX2) formed by two significant factors was revealed in the overwhelming majority of cases. On this plane, stimuli were arranged according to their intensities. This fact can be explained by specific (twilight) type of rabbit's vision with predominant discrimination of intensities. However, some findings suggest that visual evoked potentials reflect simultaneous processing of two characteristics of visual stimuli (intensity and orientation) being indicative of a possibility of the complex stimuli analysis in the primary visual cortex.