“Transient structures”: The effects of practice and distractor grouping on within-dimension conjunction searches

Abstract

It has been stated that whereas between-dimension (color x orientation) conjunctions can be searched in a "parallel" fashion, within-dimension (color x color) conjunctions are necessarily searched in a "serial self-terminating" fashion (Wolfe et al., 1990). We explored the effects of practice (within 1-h experimental session) and distractor grouping on within-dimension conjunction search tasks. In Experiments 1 and 3, the stimuli were rectangles formed by two adjacent squares; in Experiment 2, the stimuli were plus signs formed by two segments and an intersection. In Experiments 1 and 2, observers were assigned to one of two experimental conditions: In one, all the distractors shared a simple feature (the color blue); in the other, distractors did not share that simple feature. In the first condition, search became more efficient with practice and observers' performance was characterized by a shallow reaction time (RT) x set size slope; in the second condition, observers' performance did not improve as much with practice. We propose that the differential effects of practice between these two experimental conditions can be explained in terms of distractor grouping induced by the shared color of the distractors. Experiment 3 showed that, with practice, a shallow RT x set size slope characterized observers' search for a color x color target among four different distractors that shared a common color. The present results contradict a main tenet of some current visual search models--namely, that within-dimension conjunctions cannot be searched in parallel, and question the validity of using RT x set size slope functions to distinguish between preattentive versus attentive search.

The control of attentional target selection in a colour/colour conjunction task

“…Participants had to detect the presence or absence of a target object that was defined by a specific colour/ colour combination (e.g., red above green). The small display set size reduces the possibility that target selection was primarily based on the colour-based perceptual grouping of distractors, as previously found for colour/colour conjunction search with dense displays (Carrasco et al, 1998;Linnell & Hymphreys, 2001). On no-competition trials, one targetmatching object (either the target or a distractor object that matched the top or bottom colour of the target, e.g., red above blue) was presented among three nonmatching, nontarget objects.…”

“…This specific assumption is based on experiments demonstrating that search for targets defined by a conjunction of two colours or two orientations is much less efficient than search for colour/ shape conjunctions (Wolfe et al, 1990; see also Wing & Allport, 1972). However, other studies have suggested that colour/colour conjunction search can be relatively efficient (Carrasco, Ponte, Rechea, & Sampedro, 1998) and that pairs of colour/colour conjunction targets can be processed in parallel (Linnell & Hymphreys, 2001). For example , Carrasco et al (1998) showed that when all distractor objects share the same nontarget colour, practice led to highly efficient colour/colour conjunction search, presumably due to the colour-based perceptual grouping of distractors and the subsequent rapid rejection of these grouped non-target objects (see Linnell & Hymphreys, 2001;2002, for further evidence of within-dimension grouping effects in this type of search task).…”

“…However, other studies have suggested that colour/colour conjunction search can be relatively efficient (Carrasco, Ponte, Rechea, & Sampedro, 1998) and that pairs of colour/colour conjunction targets can be processed in parallel (Linnell & Hymphreys, 2001). For example , Carrasco et al (1998) showed that when all distractor objects share the same nontarget colour, practice led to highly efficient colour/colour conjunction search, presumably due to the colour-based perceptual grouping of distractors and the subsequent rapid rejection of these grouped non-target objects (see Linnell & Hymphreys, 2001;2002, for further evidence of within-dimension grouping effects in this type of search task). The assumption that colour/colour conjunction search cannot be guided by both target-defining features also has been challenged by behavioural and electrophysiological results from spatial cueing experiments (Irons, Folk, & Remington, 2012;Grubert & Eimer, in press), which suggest that search templates for multiple colours can be activated simultaneously.…”

Guidance of eye movements during conjunctive visual search: The distractor-ratio effect.

“…The guided-search model can account for this finding by assuming that participants conduct a separate evaluation of the number of red items and blue items in a display and then search through the smaller subset of distractors. This flexible change in search behaviors can be seen as another exception (see also the efficient within-dimension conjunction search with practice by Carrasco et al, 1998 and with part-whole configuration by Wolfe et al, 1994) to the general nature of inefficient within-dimension conjunction searches ).…”

“…The combination of these activations would guide attention towards the red horizontal item. However, in a within-dimension search task, activation emerges from one dimension only, and the features can be searched only in a serial fashion because it is not possible for one feature module to handle two simultaneous topdown requests for activation ; but see Carrasco, Ponte, Rechea, & Sampedro, 1998 for evidence of efficient within-dimension searches). Given the argument by Wolfe and his colleagues Wolfe et al, 1994;Wolfe, 1994Wolfe, , 1996 that within-dimension conjunction searches are processed in a qualitatively different fashion from cross-dimension conjunction searches, Experiment 2 was designed to examine whether the distractor-ratio effect is also observed in within-dimension conjunction search tasks by employing a color × color within-dimension conjunction search task.…”