Curvature formation in the visual cortex: How do we sample?

Abstract

Does the human visual system sample shapes at discrete points? During adaptation when the neurons are fatigued, one observes the underlying principles that were once less prominent than the fatigued features. Operating under deficit, these less prominent features expose the original contributions from the fatigued neurons that are now absent. An underlying lower order neural process, is thus, now revealed. In this paper, we conduct experiments using a modified version of the circle-polygon illusion in order to reveal the brain’s sampling pattern. The circle-polygon illusion produces polygonal percepts during adaptation when a static dark outline circle is pulsed at 2 Hz alternating with a gradient luminance circle. We perform two experiments. In the first experiment, we present circles of size [2,4,8,16] deg presented at eccentricity [0,1,2,4,8] deg in a cross design. In the second experiment, we modify the method of Sakurai (2014) and display arc lengths that are 1/8, 1/4, 3/8, 1/2, 5/8, 3/4, 7/8 and 1 (whole) of a circle, of size 4 and 8 deg, presented centrally. The observers report the edge length seen instead of a polygon order. We find that the stimulus size and presentation eccentricity, taken together, best explain the edge length reported by the users and that size alone is the most reasonable fixed parameter. The users, as a random effect, do not influence the mean of the edge length reported when considering the best model reported (size and eccentricity together) according to loglikelihood. However, the users do influence edge length reported only when using mean eccentricity or eccentricity as the parameter influencing edge length. Arc lengths of a circle produce same or similar edge lengths. The length of the curve does not play a significant role signifying that biological neurophysiology at an eccentricity controls the edge length formation.