Sampling limits and critical bandwidth for letter discrimination in peripheral vision

We develop and test two functional hypotheses based on the sampling theory of visual resolution that might account for letter acuity in peripheral vis ion. First, a letter smaller than the acuity limit provides insufficient ve ridical energy for performing the task, and, second, the available veridica l energy is masked by increased amounts of visible but aliased energy. Thes e two hypotheses make opposite predictions about the effect of low-pass fil tering on letter acuity, which we tested experimentally by using filtered l etters from the tumbling-E alphabet. Our results reject the masking hypothe sis in favor of the energy insufficiency hypothesis. Additional experiments in which high-pass-filtered letters were used permitted the isolation of a critical band of spatial frequencies, which is necessary and sufficient fo r achieving maximum visual acuity. This critical band varied with the parti cular pair of letters to be discriminated but was in the range 0.9-2.2 cycl es per letter. (C) 1999 Optical Society of America [S0740-3232(99)00810-8].