Figure 1.

Spatial, temporal, and spectral properties of visual stimuli. (a) The spatial structure of the stimulus consisted of a 50-degree diameter circle, with a 5-degree Gaussian envelope applied to the edge. The entire screen, as well as the stimulus background, was set to a midpoint gray. A 0.2-degree black circle was located in the center of the screen to aid fixation and obscure the foveal blue scotoma (Magnussen, Spillmann, Stürzel, & Werner, 2001). (b) Stimuli consisted of three spectral modulations that targeted the LMS (“black-white”), L-M (“red-green”), and S (“blue-yellow”) pathways. (c) Stimuli flickered sinusoidally at a rate of 1.625, 3.25, 7.5, 15, or 30 Hz. Two-second periods of flicker were followed by a 3-s response window during which the midpoint gray screen returned.