The Tilt Illusion and Orientation Sensitivity

Abstract

Line orientation was evaluated under different observation conditions. In the first experiment, the distortion in the estimation of line orientation was 1°–9° in the presence of adjacent lines with different orientation (the tilt illusion). The illusion was stronger and the orientation discrimination thresholds were higher when the line length decreased up to 6 arcmin. For 6 arcmin lines, the illusion was approximated by a model where orientation was determined by the tilt of the minimal receptive fields (RFs) whose neurons had the maximal responses. The model was validated in the second experiment, when the minimal length for vertical and horizontal lines discrimination was determined. The minimal length was consistent with the width of the model RFs areas. The RF interactions affecting the illusion were evaluated in the third experiment where the orientation discrimination of lines with a length of 60 arcmin was studied. Age-related orientation dependencies allow a suggestion that the interactions between RFs reduce the tilt illusions.