Abstract

Resolution acuity is often conceived as that spatial frequency for which contrast sensitivity fails to unity. We suspect this is not the case for peripheral vision because recent experiments have shown that peripheral resolution is limited by the ambiguity introduced by aliasing, not by an inability to detect the stimulus.^1,2 Since gratings beyond the resolution limit remain highly visible as aliased percepts, we predict that contrast sensitivity for detection will be well above unity at the resolution limit. Using a two-interval forced choice staircase paradigm we measured contrast sensitivity for detection of a 2.3° patch of grating (vs uniform field) displayed on an oscilloscope located 30° into the horizontal nasal visual field and having mean luminance of 80 cd/m². The resolution limit was separately determined by the method of adjustment as the highest spatial frequency for which perception is veridical and aliasing does not occur.¹ We find that peripheral contrast sensitivity has a bandpass characteristic which peaks at ~1.5 c/d and falls monotonically with spatial frequency up to the detection limit of ~20 c/d. The function passes smoothly through the resolution limit of 3.2 c/d, where sensitivity is about an order of magnitude above the absolute threshold of unity.

© 1988 Optical Society of America