Direct measurements of 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 2
capital letters (letter height = 1.3°, width = 0.9°, eccentricity = 5.5°). 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° to more than 10° of visual angle. Experiment 2 yielded similar results
with triples of letters. Experiment 3 showed that accuracy increased with spatial
separation for report of 2 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.