The stimuli were vertical cosine gratings of at least four cycles in width with a circular vignette envelope. Contrast thresholds were measured for spatial frequencies of 0.26, 0.58, 1.11, 2.17, 4.29, and 8.53 cpd. The viewing distance for 4.29 cpd and lower was 57 cm, and for 8.53 cpd it was 114 cm. The duration of the stimulus was 1.053 seconds, and the interstimulus interval was 583 ms.
For suprathreshold contrast matching, two horizontally separated gratings were presented. The standard grating, with a fixed spatial frequency of 0.58 cpd, was on the right of the display screen and was presented at seven contrast levels: 1.7%, 3.6%, 7.2%, 13.7%, 27.9%, 41.5%, and 55.9%. The test grating, with varying spatial frequency of 0.26, 0.58, 1.11, 2.17, 4.29, or 8.53 cpd, was presented on the left.