Aliasing for rapidly counterphasing stimuli: a failure to demonstrate an M-cell sampling limit to resolution.

We investigated whether resolution is sampling limited for stimuli optimized for detection by magnocellular mechanisms. We measured peripheral (15 degrees and 30 degrees) spatial detection and resolution thresholds using 50% and 90% contrast flicker-defined gratings (25 Hz) and 90% contrast counterphasing sinusoidal gratings (25 Hz). Direction-discrimination performance for 90% contrast counterphasing sinusoidal gratings (25 Hz) was measured foveally. Our results indicate that resolution of rapidly counterphasing stimuli is sampling limited in peripheral vision but is consistent with limiting of performance by parvocellular mechanisms. Also, undersampling may not be necessary to account for motion reversals observed with gratings that both drift and flicker.