Human Systems Integration Division @ NASA Ames

When two moving patterns of spatial noise are combined additively, a percept of two "transparent" sheets is evoked. When the number of moving patterns is increased beyond two, subjects are no longer able to perceive all of the patterns simultaneously, although the composite sequence is easily distinguished from dynamic random noise, and individual moving patterns can be identified and tracked. This result can be demonstrated experimentally by asking subjects to discriminate 2 planes from 3, 3 from 4, etc.; when the stimuli are controlled to eliminate cues other than the motions, for exposure durations up to 250 ms. this task is virtually impossible for more than two planes. The case of two plane transparency, on the other hand, can easily be identified with an exposure duration as brief as 60 ms.

Distributed representations of motion have been proposed to account for the phenomenon of motion transparency: in these models, the transparent sheets are represented by different peaks in the distribution of activity. The present results suggest a later stage which segments the motion information, with only two populations of neurons available to latch onto an identified direction of motion. Supported by NASA RTOP 505-64-53.