It is well documented that people are able to distribute their attention broadly across space to extract information about the spatial distribution of particular visual features, which is called feature-based attention. This experiment investigated whether or not training could enable observers to sharpen the tuning of attention filter for spatial frequency. Stimuli were spatially random displays of vertically oriented Gabor patterns. On each trial, the subject strove to mouse-click the centroid of 3 Gabor patterns while ignoring 12 other “distractor” Gabor patterns, 6 each with frequencies higher and lower than the target frequency. The mean absolute difference between the frequencies of the distractors vs. the target (called the “spread” of the stimulus) determined the difficulty level of the trials. The smaller the spread, the harder a trial is. Spread was controlled by a three-up one-down staircase. The experiment had eight days, and at the beginning of each day, the subject had a testing session to establish the baseline of their attention filter before having the training session. The hypothesis was that threshold spread would show a decrease with training. No such effect was observed. This suggests that the tuning of a subject’s attention filter for spatial frequency cannot be sharpened with training.
Download PDF Abstract 1The centroid task is an important tool used to study feature-based attention. In the centroid task, a participant uses a mouse to indicate the perceived centroid of a "cloud" of briefly-displayed stimulus items. Backward structure masks are routinely used in this task to limit the availability of information about the items in the stimulus cloud, thus eliminating the possibility of attention shifts. These masks consist of an array of elements that fill the display and are similar to the items in the stimulus cloud. Participants in centroid tasks often report that stimulus items seem to be "drawn to" or otherwise confused with subsequent mask elements. This experiment was designed to test whether the spatial relation between stimulus items and mask elements changed the perceived position of the stimulus items in any way that interfered with centroid judgments. To do this, stimulus clouds were presented consisting of eight items. In one condition, four of these items were presented at the location of a subsequent mask element and the other four were displaced from the location of the nearest subsequent mask element. In a second condition, all eight items were aligned with subsequent mask elements. A variety of analyses found no effect on the centroid responses that depended on whether stimulus items were aligned or displaced. This result is surprising since it contradicts participant introspections; at the same time, however, the lack of an effect simplifies interpretation of centroid data collected using backward masks.
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