Abstract
Duration thresholds were obtained for a single test stripe succeeded by a masking pattern of alternating dark and bright bars delivered to the same retinal region. The effect of the angle (alpha) between test stripe and masking contours was studied in conjunction with both vertical and horizontal test stripes. With either of the test-stripe orientations duration threshold decreased as alpha increased from 0° to 90°. In another experiment both alpha and the interstimulus interval (ISI) were varied. The effectiveness of alpha as a determinant of masking seemed to be restricted to ISI below 60 msec.