Effects of spatial separation between stimuli in whole report from brief visual displays

Direct measurements of the effects of spatial separation between stimuli in whole report from brief visual displays are reported. The stimuli were presented on the periphery of an imaginary circle centered on fixation. In Experiment 1, each display showed two capital letters (letter height approximately equal 1.3 degrees, width approximately equal 0.9 degree, eccentricity approximately equal 5.5 degrees). The proportion of correctly reported letters was a strictly increasing, decelerating function of the spatial separation between the letters for center-to-center separations ranging from less than 2 degrees to more than 10 degrees of visual angle. Experiment 2 yielded similar results with triples of letters. Experiment 3 showed that accuracy increased with spatial separation for report of two short words, and Experiment 4 showed the same result for words presented upside down. The results are explained by a model of lateral masking (crowding) based on competitive interactions within receptive fields of cortical neurons.