A pixel-resolution video switcher for eye-contingent display changes

Moving-mask and moving-window paradigms are used to study the spatial and temporal aspects of visual information processing. Due to technical limitations, these paradigms have frequently been applied to reading, but only rarely to scene perception. Existing moving-mask or moving-window techniques for graphical stimuli usually blank the display inside or outside a square window, respectively. A new moving-window technique is presented here that uses a purpose-designed video switcher and three synchronized video boards. The first video board contains the stimulus presented inside the window. The second video board contains the stimulus to be presented outside the window. The third video board contains a black-and-white image of the window that is used as a key signal for the video switcher. The video switcher selects between the video signals of the first and the second video board on a pixel-by-pixel basis, controlled by the key signal generated by the third video board. By panning the image of the third video board, the window can be moved very rapidly. Here we use oval windows, centered on the fixation spot as measured by an eye-tracker. The normal stimulus is visible inside the window, whereas manipulated information is presented outside the window, or vice versa.