The perception of spatial order at a glance.

Spatial order is the organizing principle of the visual areas in the brain. But to what extent does this spatial mapping help us see where things are? Observers trained to perfectly recall the spatial order of seven items presented simultaneously for 5 s were asked to report their order when flashed for only 150 ms. We found that the capacity for perceiving the order of these brief stimuli was limited by their spacing. Five or six widely-spaced stimuli were seen in the correct order, but only four crowded stimuli. Regardless of spacing and set-size, confusions between neighbors were unexpectedly frequent, suggesting there is positional as well as object uncertainty.