Previewing distractors reduce efficiency of visual processing at previewed locations
56.307, Tuesday, May 14, 2:45 - 6:45 pm, Royal Ballroom 6-8
Takayuki Osugi1, Ikuya Murakami1; 1Department of Life Sciences, The University of Tokyo
When some of distractors (old items) appear before others (new items) in an inefficient visual search task, the old items are excluded from the search (visual marking). Visual marking occurs possibly because the locations of the old items are inhibited before the new items appear. Sensitivity to contrast increments at the old locations has been shown to become lower than that at the new locations. What process plays a key role in reducing sensitivity? The present study took advantage of the equivalent noise analysis to examine whether the sensitivity reduction occurs due to an increase in internal equivalent noise (IEN) or due to a decrease in calculation efficiency (CE). To determine these parameters, we measured contrast thresholds for a Gaussian luminance blob as a function of external noise contrast. This detection task was combined with the preview search task in which the old items were presented for 1 s before the new items were added. The target to be searched for could be present only within the new items. At 200 ms after the onset of the new items, a blob appeared for 100 ms in half of all trials. All stimuli were embedded in various amounts of external noise, i.e., dynamic random luminance noise. Following speeded reaction for search, participants were asked to report whether a blob had appeared. The parameters estimated from the threshold versus noise contrast function indicated that CE at the old locations was lower than that at the new locations, whereas the IEN did not increase at the old locations. Therefore, the sensitivity reduction at the old location is attributable to the decrease in CE. Some inhibitory template for visual marking effectively operates by depriving previewed sterile locations of limited attentional resources, such as time and resolution, for target search.