Abstract
A vivid, color-changing display was created by continuously cycling 300 randomly-colored dots through the color wheel. Surprisingly, when this display was rotated about its center, the color-change appeared to halt. In one experiment, the display alternated between rotating and remaining still, and observers were asked to adjust the rate of color-change when the annulus was still to match the apparent rate of color-change when the annulus moved. We found that, as the angular velocity of the annulus increased, the matched rate of color-change decreased. At high angular velocities (180 deg/s), observers reported a nearly-complete halt in color-change. We suggest that the transients produced by the dot' motion cause transients produced by color-change to go unnoticed, updating silently. Next, we examined how transients produced by continuous changes in two dimensions, position (motion) and luminance (twinkle), interacted when one was dominant. Twelve dots appeared in a ring, centered about fixation (dot radius = 0.5 deg, ring radius = 10 deg). In a blocked design, observers were asked to report which one of the 12 dots moved or twinkled, while simultaneously, all of the dots changed along the other dimension. We measured thresholds for detecting the specified change, and found that they rose by as much as a factor of four when the amplitude of change along the irrelevant dimension was increased. The reported interference suggests that transient signals produced by one dimension can suppress transient signals produced by other dimensions; this may play an important role in controlling which changes in the visual field capture attention, and which will fail to capture attention, updating silently.