Abstract

When the luminance contrast of the second target in Braddick-type two-frame random-dot cinematograms (RDC) is reversed, one sees a motion in a direction opposite to physical displacement. Direction discrimination characteristics for this reversed motion were examined as a function of target displacement, using 4 × 4° random-dot fields with a 2 × 2° target consisting of 2–8-min dots. The percent seeing the reversed motion was ~100% when displacement was small and approached chance level as displacement was increased. The displacement limit for observing the reversed motion was quite similar to D_max for regular RDC, and related to visual angle rather than to number of dots. These results indicate a possibility that the same short-range process underlies the motion discrimination in both normal and reversed motion. However, when performance of motion discrimination and figural segregation in regular and reversed RDC were compared in another experiment using a rectangular target, the performance for figural segregation (discrimination of target orientation) was considerably impaired for the reversed RDC. The results suggest that the so-called short-range process should be treated as having two distinct components, i.e., one for motion discrimination and the other for pattern segregation.

© 1986 Optical Society of America