Sensitivity to phase distortions in central and peripheral vision

Abstract

Sensitivity to phase quantization of a two-dimensional random texture pattern was investigated in central and peripheral vision, using the method of Caelli and Bevan (1982). The random texture was phase quantized with two-octave-wide bands centered on spatial frequencies of 2, 4, 8, and 16 cycles per degree (cpd). For each of these bands, six modified versions of the original texture were prepared using different degrees of phase quantization: 24 steps of 15°, 8 steps of 45°, 5 steps of 72°, 4 steps of 90°, 3 steps of 120°, and 2 steps of 180°. The task of the subject was to discriminate between the original texture and each of the six phase-distorted versions. The amount of stimulus contrast required for threshold discrimination of each stimulus pair was determined using a two-alternative, forced-choice paradigm combined with a maximum-likelihood staircase procedure. Stimuli were presented sequentially at exposure durations of 1,000 and 125 msec. Subjects viewed the stimuli with foveal vision or 2° in the right peripheral visual field. The results show that maximum sensitivity to phase quantization is found in the 4 cpd spatial frequency band and that sensitivity is greatly reduced with peripheral vision. Sensitivity to phase quantization is higher with 1,000- than with 125-msec exposure duration. © 1985 Psychonomic Society, Inc.