Effects of interactions of two moving lines on single unit responses in the cat's visual cortex

Representation of spatial details in textured patterns by cells of the cat striate cortex

The ability of single cells to represent the spatial details of textured stimuli was investigated. Two complementary aspects of cell response were considered, the ability to discriminate fine stimulus details and the property of integration over wider areas of a structure to encode differences in mean luminance. Responses of simple and complex cells were distinct in some respects. Spatial discrimination: Simple cells would encode orientation of line arrays as long as individual line elements could be spatially resolved. By contrast, complex cells were able to distinguish the orientation of texture areas even when the individual lines of the stimulus were not resolved in their response. Threshold sensitivity for texture orientation was of the same order in both cell classes despite differences in receptive field size. Spatial integration: Complex cells responded to texture luminance differences of much coarser patterns than did simple cells. These responses, however, were not biased for contour orientation unless finer patterns were used. Only with very fine textures did responses become indistinguishable from those to uniform stimuli for both simple and complex cells. For complex cells, there was a smooth transition from resolution to fusion of spatial details with increasing structural density. Simple cells were insensitive to both detailed and global properties of a stimulus pattern over a wide range of texture density. Implications for alternative measures of visual acuity of single cells are discussed.

Neural interactions of two slits in the orientation domain in the visual cortical units of the cat

The responses of the cat's visual cortical cells to an optimally oriented (O-) and an inclined (theta-) slit have been studied. Cell's responses to the simultaneous presentation, in simple cells, are similar to those to theta-slit alone, but in complex cells, are remarkably decreased at orientation difference of about 45 degrees. In the sequential presentation, the effects of preceding theta-slit on the responses to the following O-slit decrease as the orientation difference increases. This suggests that neural interactions of simultaneous and sequential presentation of two slits are caused by different mechanisms.

A model for the monocular line orientation analyzer

A model for monocular line perception by human Ss is based on three basic assumptions: (a) the line's inclination is coded by the maximally excited orientation detector's number; (b) the inclination of the perceived line is equivocally determined by the excitation vector in the subjective space; (c) the analyzer has a maximum differential sensitivity over the whole range of the line inclinations. This simple model for the line inclination analyzer, taking into account the optimization of its sensitivity, provides incomplex explanations for a wide range of psychophysical and neurophysiological data obtained from human and animal experiments.

Visual control of orientation behaviour in the fly. Part II. Towards the underlying neural interactions

Visual information processing in the nervous system of flies begins with a large array of photoreceptors, which transduce a light intensity pattern, and culminates in a behavioural response that depends on that pattern.

In the previous paper we have given a quantitative description of visual control of flight orientation in the fly. This description can account for fixation, tracking and some instances of spontaneous pattern preference behaviour. The phenomenological theory outlines the basic logical organization of the visual control system of the fly. It requires the neural network between the receptors and the flight muscles to perform two main computations on the visual input. One computation extractsmovementinformation (the termr(ψ)ψ b of the phenomenological equation). The other provides position information (the termD(ψ)).