Visual search for singleton feature targets within and across feature dimensions

Abstract

Three experiments investigated visual search for singleton feature targets. The critical dimension on which the target differed from the nontargets was either known in advance or unknown-that is, the critical difference varied either within a dimension or across dimensions. Previous work (Treisman, 1988) had shown that, while the search reaction time (RT) functions were flat in both conditions, there was an intercept cost for the cross-dimension condition. Experiment 1 examined whether this cost would disappear when responses could be based on the detection of any (targetnontarget) difference in the display (by requiring a "heterogeneity/homogeneity" decision). The cost remained. This argues that pop-out requires (or involves) knowledge of the particular dimension in which an odd-one-out target differs from the nontargets; furthermore, that knowledge is acquired through the elimination of dimensions not containing a target. In Experiment 2, the subjects had to eliminate (or ignore) one potential source of difference in order to give a positive response (displays could contain a "noncritical" difference requiring a negative response). The result was a comparatively large cost in the within-dimension (positive) condition. This can be taken to indicate that popout as such does not make available information as to the particular feature value in which the target differs from the nontargets. Experiment 3 examined whether search priorities can be biased in accordance with advance knowledge of the likely source of difference. The subjects were found to have a high degree of top-down control over what particular dimension to assign priority of checking to. The implication of the results for models of visual search and selection are discussed.Much recent research in visual perception has attempted to understand how humans detect a (usually known) target stimulus in a background of nontargets (distractors; see, e.g., Cave & Wolfe, 1990; Treisman & Gelade, 1980; Treisman & Sato, 1990;Wolfe, 1994). This work has used the analysis of reaction times (RTs) as a function of the number of items in the display (the display size) as its major tool. Two different patterns of RT/ display size functions are typically observed. Which pattern is found depends on the nature ofthe target and nontarget stimuli. When the search involves a target that differs from nontargets in a single salient feature (e.g., a vertical line amongst horizontal lines), the search RT functions are flat, supporting the notion that targets are detected by a spatially parallel process. In contrast, when the target is defined by a conjunction offeatures, each of which is separately present among the nontarget items (e.g., a red X among red Os and greenXs), the search RT functions are linearly increasing and the slope ratios between target absent and present responses are approximately 2: 1. This pattern has been taken as indicative of a spatially serial search process, where search is exhaustive on absent trials and self-terminates upon detecting a target on pr...

Distinct neural networks for target feature versus dimension changes in visual search, as revealed by EEG and fMRI

“…For instance, in search for an "odd-one-out", changing the target feature from a smaller item to a larger item or from a red item to a green item slows responses to the target (e.g., Maljkovic & Nakayama, 1994;Becker, 2008aBecker, ,b,c, 2010. Similar switch costs occur when the stimulus dimension of the target is changed, for example, from a target differing in size to a target differing in color (e.g., a large to a red target; Müller, Heller & Ziegler, 1995).…”

“…According to this attentional biasing account, selection of the target feature or the target dimension primes or biases attention to select the same feature or dimension on the next trial, by increasing the weights (or gains) of corresponding feature-specific and dimension-specific maps, respectively (e.g., Maljkovic & Nakayama, 1994;Müller et al, 1995).…”

Selective and interactive neural correlates of visual dimension changes and response changes

“…The dimension weighting account (Mü ller et al, 1995;Found and Mü ller, 1996) proposes that, in the case of a dimension change, attentional weight is reallocated from the old to the new targetdefining dimension. The current activation pattern supports this view: there was a large activation in right fusiform gyrus, at a location that has previously been reported to be a potential source of the P1 event-related electric brain potential, which itself is modulated by selective attention (Heinze et al, 1994).…”

“…In contrast, no such change costs are observed when the target is defined by a different feature within the same dimension (e.g., a red target following a blue target). To explain this pattern of results, Mü ller et al (1995) proposed a Fdimension-weighting_ account, according to which there is a limit to the total amount of attention, or attentional weight (cf. Bundesen, 1990;Duncan and Humphreys, 1989), available to be allocated to objects' dimensions.…”

“…Recently, a debate has arisen in the behavioral literature as to whether dimension change effects are perceptual or, respectively, response-related in nature or whether they reflect both perceptual and response-related processes (see Mü ller and Krummenacher, in press, for a review). In more detail, Mü ller and his colleagues (e.g., Mü ller et al, 1995Mü ller et al, , 2003Found and Mü ller, 1996;Krummenacher et al, 2001Krummenacher et al, , 2002a interpreted these effects as arising at a pre-attentive perceptual stage of processing that guides the allocation of focal attention to the target (based on preattentively computed feature difference signals). This interpretation has recently been challenged by Cohen (Cohen and Magen, 1999;Cohen and Feintuch, 2002;Feintuch and Cohen, 2002;Cohen and Shoup, 1997) and Theeuwes (Mortier et al, 2005;Theeuwes et al, in press; see also Theeuwes, 1992Theeuwes, , 1996, who argued that the dimension change effects reflect post-selective response stage processes, which follow the allocation of focal attention to the singleton feature target (with attentional allocation itself being uninfluenced by dimension weighting).…”