Visual Resolution of Two-Bar Patterns and Square-Wave Gratings*

Contrast thresholds for resolution were measured with two types of display: (1) a test field of constant size filled by square-wave gratings of spatial frequencies between 0.44 and 8.75 cycles/deg; (2) two bright bars, comprising $1\frac{1}{2}$ cycles of the square-wave gratings. Results show that even with $1\frac{1}{2}$ cycles, there is some decline of contrast sensitivity at low spatial frequencies, and an interaction between the effects of exposure duration and spatial frequency. However, data obtained with gratings of constant size can give an exaggerated impression of the magnitude of inhibitory interactions in the visual nervous system.