Dipole analysis of the influence of linear arrays of points on visually perceived eye level (VPEL)

Previous research has shown that a visual field consisting of as little as one peripherally located luminous line that is pitched from vertical in a dark field induces large changes in an observer's visually perceived eye level (VPEL). The effects of this severely reduced inducing stimulus are surprisingly close to the effects of a highly structured pitched visual field. In the present report we describe two experiments with inducing stimuli that were still further reduced to one or two linear arrays of points of light. The results show that the array's effect on VPEL increases as a negatively accelerated increasing function of the amount of stimulus (i.e., the length of the array, the number of points, and the interpoint separation). We propose a multiscale dipole model (MDM), which quantifies the effect of the array of points on VPEL in terms of dipoles of various lengths that activate orientation and size specific neurons in visual cortex. For example, when the number of points increases in an array of fixed length, dipoles of progressively shorter length are created within the overall length of the stimulus. The shorter dipoles stimulate additional orientation-selective neurons with smaller receptive fields whose neural activity adds to the activity generated by the larger dipoles up to a saturation limit. The functional relation between the psychophysical response and the number of dipoles can be modeled as a rectangular hyperbola, formally similar to equations that have been used to model saturation binding and enzyme velocity in biochemistry and contrast response functions in neurophysiology and psychophysics.