Brief foveal masking during scene perception.

In the present experiment, participants were exploring line drawings of scenes in the context of an object-decision task, while eye-contingent display changes manipulated the appearance of the foveal part of the image. Foveal information was replaced by an ovoid noise mask for 83 ms, after a preset delay of 15, 35, 60, or 85 ms following the onset of fixations. In control conditions, a red ellipse appeared for 83 ms, centered around the fixation position, after the same delays as in the noise-mask conditions. It was found that scene exploration was hampered especially when foveal masking occurred early during fixations, replicating earlier findings. Furthermore, fixation durations were shown to increase linearly as the mask delay decreased, which validates the fixation duration as a measure of perceptual processing speed.

Scene exploration with Fourier-filtered peripheral information.

In a previous moving-window study it was found that scene exploration benefits more from peripheral information of high spatial frequency than of low spatial frequency. In the present study, degraded versions of realistic scenes were presented peripherally during the initial 150 ms of fixations, while the undegraded scene was presented foveally. The undegraded version of the scene was visible both foveally and peripherally during the later part of fixations. During the initial 150 ms, the peripheral part of scenes was low-pass, bandpass, or high-pass filtered, blanked, or decreased in luminance. In a no-change condition, the undegraded scene was presented throughout the whole fixation. Participants freely explored the scenes in the context of an object-decision task. It was found that degrading peripheral information during the initial part of fixations had minimal effect on scene exploration. No reliable differences were found among the three filter types. The results indicate that, in the context of an object-search task, peripheral information is of minor importance during the initial part of fixations.

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.