Figure 1.

Crowding demos. In each column, while fixating the black square, try to identify the center letter in the upper or lower demo. That is the target. It is black in the upper demo and white in the lower demo. Crowding scales with eccentricity, so these demos work at any viewing distance. (The 10° target eccentricity used in the Experiment reported in Figure 2 corresponds to viewing this figure at 100% magnification from about 6 cm, or at 400% from 24 cm. But the viewing distance hardly matters.) Critical spacing varies among people. Our demos work for most people, but if you are particularly susceptible or resistant to crowding, the demos might be too hard or too easy. You can compensate for this by fixating a bit above or below the black fixation square, to adjust the eccentricity of the target. (A) With no flankers, it is easy to identify the target letter. (B) One ring of same-polarity flankers, far away, does not crowd the target. (C) One ring of same-polarity flankers, nearby, crowds the target. Panels B and C show the same condition at different spacings to demonstrate the effect of proximity on crowding. (D) One ring of opposite-polarity flankers does not crowd a target. (E) Two rings of same-polarity flankers do crowd a target. (F) Two rings of opposite-polarity flankers do not crowd a target. (G) Surprisingly, a near ring of opposite-polarity flankers and a far ring of same-polarity flankers, both of which do not produce crowding alone, do crowd a target when presented together. (H) Three rings of alternating-polarity flankers crowd a target as strongly as two rings of alternating-polarity flankers. (B–H) For each condition we test many spacings, ranging from near to far, controlled by QUEST, to determine threshold, i.e., critical spacing.