Characteristics of the Visual System: Psychophysical Measurements of the Response to Spatial Sine-Wave Stimuli in the Photopic Region*

The perceived brightnesses of the maxima and minima in spatial sinusoidal light variations have been determined by suprathreshold psychophysical techniques in the photopic region. For example, the response/ stimulus contrast ratio at 20 cd/m2 average luminance and spatial frequencies between 1.5 to 7.5 lines/deg is 2.4 to 3.4 for 25% and 1.8 to 2.0 for 50% object contrast. Contrast transfer has a pronounced peak at about 5.5 lines/deg for all object contrasts. The visual system is nonlinear and a contrast transfer function does not exist in the photopic region. The measurements have been performed under normal viewing conditions where both successive and simultaneous contrast phenomena are operative.