Fig. 2.

A. Two-ring experiments. We fixed the size and position of the inner flanks and added a second set of flanks (i.e., two flanking rings). In one experiment we fixed the size of the second ring and varied its distance (squares), in the other, we fixed the outer edge of the second ring and varied the flank size (triangles). The circle shows the threshold elevation with the inner flank alone. B. Varying the number (and location) of flanking segments. Increasing the number of flank segments (N) from 1 to 4 has a substantial effect, following the prediction of linear integration of independent segments (black dashed line). Increasing the number of segments from 4 to 8 (a full annular surround) results in slightly reduced crowding. The dashed line shows the prediction of linear integration of independent segments, with threshold increasing in proportion to √N for N>1 (N = 1 is taken as the measured elevation with a single flank). The insets show examples of 1 “inner” flank (i.e., between the fixation point [which was 5 deg above the target] and the target; 2 “tangential” flanks; 4 and 8 flanks. C. Gaps in the annulus. Top. The flanks consisted of an annular surround consisting of either 4 (small circles) or 8 (large circles) wedges of grating with variable sized gaps of uniform gray between the wedges. Increasing the gap width (lower abscissa) results in increased crowding. The larger the gap, the smaller the amount of flanking grating (top abscissa).