WHEN STEREOPSIS DOES NOT IMPROVE WITH INCREASING CONTRAST

It is well known that stereoacuity for conventional (Isr-order) stimul i improves with increasing contrast with an approximate slope of -0.5 on log-log axes (Halpern DL, Blake RR. Perception 1988;17:483-495; Leg ge GE, Gu Y. Vis Res 1989;29:989-1004). In the experiments reported he re a variety of stimuli were used (Gabor patches, amplitude modulated stimuli and 1D noise patches) and tasks (stereoacuity and D-max) to de termine if 2nd-order stereopsis shows a similar square root dependence . The results consistently demonstrate that the effect of contrast on stereopsis is quite different for the 2nd-order stimuli. Increases in stimulus contrast have little effect on performance; the resulting slo pes are very shallow. The pattern of results is similar when the inter ocular contrast ratio is varied, demonstrating that 2nd-order processi ng is more resilient to stimulus differences in the two eyes than Ist- order. (C) 1998 Elsevier Science Ltd. All rights reserved.