Preattentive and cognitive effects on perceptual completion at the blind spot.

Our findings indicate that preattentive processes, such as the filling in of homogeneously colored areas, discrete dots, or bars across the blind spot, take into account both the color and the form that stimulate the retina around the optic disk. Perceptual completion of the "junction" of two opposite colors facing each other on opposite sides of the blind spot was resolved by simultaneous segregation of the two colors at the location of a filled-in perpendicular line that suggested a boundary separating the two colors. Orientation preference and relative salience of one color versus the other determined which color was perceptually completed in a forced-choice situation that involved perceptual completion at the intersection of a cross formed by bars of opposite colors. A 1-min exposure to these stimuli presented an ambiguous situation for perceptual completion of either color within the blind spot, and resulted in a perceptual "flip-flop" from one color to the other, much like the phenomenon that occurs in figure reversal. Instructions to speed up this reversal process led to a fivefold reduction in latency to first reversal.