How do I change achromatic contrast in percentage of a sinusoidal grating?
How do I change spatial frequency in cycles/degree?
How do I change grating orientation pseudo-randomly?
How do I reverse grating phase?
Original text: "These two experiments were based on a common dataset, which independently varied spatial frequency and contrast. Subjects were presented with gratings of differing achromatic contrast (1.43%, 5.25%, 15.95%, 50.14%, and 99. 62%) and spatial frequency (0.1, 0.27, 0.73, 2.08, and 5.79 cycles/degree) across different blocks, in a 5 × 5 design. Every 4 s, grating orientation changed pseudo-randomly. In addition, grating phase reversed every 1 s, and grating phase was systematically varied. Each run included 15 blocks of 16 s each, beginning and ending with an additional block (12 s) of uniform gray, of equivalent mean luminance. Each subject participated in 2 scan sessions, with 12 runs (1056 functional volumes) per session. Experiment 3 analyzed variations in contrast, combining spatial frequency. Experiment 4 did the reverse."