The effect of stimulus line variations on visual orientation with head upright and tilted

Abstract

The effects of different line length, width, and luminance on the visual vertical with head upright and tilted were investigated in 5 experiments. With head upright the visual vertical was located accurately under all combinations of stimulus properties. With 30[ddot] head tilt the E-effect was produced, and its magnitude was not affected by variations in line luminance and width (at constant luminous flux). The E-effect was reduced by increased line width (at constant luminance) and length. The former was attributed to an interaction between line width and luminance. The latter was considered to be due to differential eye movements when scanning a longer line, as brief presentation of the line abolished the line length difference. Although the variations in the E-effect were small relative to the orientation constancy operating, consideration should be given to the stimulus properties used when comparing data from different experiments.