Parallel visual processing: Constant same-different decision latency with two to fourteen shapes

Fourteen Os were shown 2, 5, 8, 11, or 14 geometric shapes at a 200-msec exposure. The maximum visual extent was the same for all numbers of shapes. The stimulus conditions were: all shapes identical, 1 shape different from the rest, and, for 5 to 14 shapes, 3 shapes different (4 shapes in all). The number of shapes, the condition, and the shapes used varied randomly through the sequence of 160 exposures. Decision latency to correct same or different response was independent of the number of shapes presented. Correct same and three-different decisions were faster than one-different decisions, but with two shapes different decisions were faster than same. The results suggest that same-different decisions are made with information processed in parallel from many stimuli