Academic journal article Attention, Perception and Psychophysics

The Unilateral Field Advantage in Repetition Detection: Effects of Perceptual Grouping and Task Demands

Academic journal article Attention, Perception and Psychophysics

The Unilateral Field Advantage in Repetition Detection: Effects of Perceptual Grouping and Task Demands

Article excerpt

This study examines interhemispheric interactions in detecting objects that are simultaneously repeated in an array of objects. Previous studies have shown that presenting two identical objects to a single hemifield speeds up repetition detection. This unilateral field advantage (UFA) is often attributed to the relatively low-level processing demands for detecting a perceptual repetition, and more specifically, to more efficient perceptual grouping processes within a hemisphere than between hemispheres. To directly examine the impact of perceptual grouping and task demands on interhemispheric interactions, we asked participants to judge whether four items, one presented in each visual quadrant, were all different, or whether any two were the same, along an instructed dimension. We found that in comparison with the UFA for identical objects, the UFA for repetition detection in accuracy was similar or greater when the matching objects were not perceptually identical and differed in color, size, or viewpoint. Thus, decreasing grouping strength and increasing computational complexity did not reduce the UFA. Results are interpreted in terms of the callosal degradation account of the UFA.

From grocery shopping to interpreting scientif ic graphs, many activities require humans to identify visual objects and compare them with neighboring objects. One simplified laboratory task that taps into the identification and comparison processes is the "repetition-detection" task (Cavanagh & Parkman, 1972), in which objects are presented simultaneously in an array for participants to detect the repetition of two identical objects. When there are relatively few objects arranged symmetrically in the field (Figure 1), repetition detection is faster when the repeated objects are presented within a single visual hemifield rather than in both visual hemifields (Butcher & Cavanagh, 2008; Weissman, Banich, & Puente, 2000).1 This unilateral field advantage (UFA) has been attributed to the engagement of relatively simple, low-level perceptual matching processes (Banich & Belger, 1990) that are more efficiently performed within a hemisphere than across hemispheres (Butcher & Cavanagh, 2008).

This study examines whether perceptual grouping can provide a full account of the UFA by manipulating perceptual grouping strength and task demands. We adopt the four-element symmetrical display2 used by Butcher and Cavanagh (2008), which yields a robust UFA for repetition detection of colors, letters, orientations, circle sizes, and motion directions. The unique aspect of our study is that we ask participants to detect the repetition of a specific stimulus property while varying other properties of the stimuli. In Experiment 1, participants were asked to detect a repetition in either the color or the letterform of letters. The repeated letters could be identical (e.g., two red "A"s) or differ along the irrelevant dimension (e.g., a red "A" and a green "A," in the case of the letterform task). Perceptual grouping strength is reduced when the repeated letters differ in one dimension. In addition, the demand for selecting the relevant dimension for comparison is increased. If the UFA is weakened by decreased perceptual grouping or by increased task demand, then it should be weaker when the repeated letters differ in color than when they are identical. Experiment 2 used a similar logic to test whether the UFA in detecting repeated shapes is weakened when the repeated objects differ in size or viewpoint. Experiment 3 focused on one-dimensional objects (e.g., color patches) but manipulated perceptual grouping and task demands by making the repeated colors distinctive or similar to unrepeated colors. We examined whether simple predictions derived from accounts based on perceptual grouping or task complexity would hold in these experiments. To avoid multiple eye fixations, we used briefly presented visual displays and focused on response accuracy. …

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