Perceived depth in the 'sieve effect' and exclusive binocular rivalry

An impression of a surface seen through holes is created when one fuses dichoptic pairs of discs, with one member of each pair black and the other member white. This is referred to as the 'sieve effect'. The stimulus contains no positional disparities. Howard (1995, Perception 24 67-74) noted qualitatively that the sieve effect occurs when the rivalrous regions are within the range of sizes, contrasts, and relative sizes where exclusive rivalry occurs, rather than binocular lustre, stimulus combination, or dominant rivalry. This suggests that perceived depth in the sieve effect should be at a maximum when exclusive rivalry is most prominent. We used a disparity depth probe to measure the magnitude of perceived depth in the sieve effect as a function of the sizes, contrasts, and relative sizes of the rivalrous regions. We also measured the rate of exclusive rivalry of the same stimuli under the same conditions. Perceived depth and the rate of exclusive rivalry were affected in the same way by each of the three variables. Furthermore, perceived depth and the rate of exclusive rivalry were affected in the same way by changes in vergence angle, although the configuration of the stimulus surface was held constant. These findings confirm the hypothesis that the sieve effect is correlated with the incidence of exclusive rivalry.