Academic journal article Memory & Cognition

Are Spatial and Dimensional Attention Separate? Evidence from Posner, Stroop, and Eriksen Tasks

Academic journal article Memory & Cognition

Are Spatial and Dimensional Attention Separate? Evidence from Posner, Stroop, and Eriksen Tasks

Article excerpt

Do various operational definitions of visual attention tap the same underlying process? To address this question, we probed visual selective attention using orientation of attention, flanker, and Stroop tasks. These were embedded in combined designs that enabled assessment of each effect, as well as their interaction. For the orientation task, performance was poorer at unexpected than at expected locations. The flanker effects also differed across the two locations. In contrast, the Stroop effects were comparable at expected and unexpected locations. We conclude that spatial attention (tapped by the orientation and the flanker tasks) and dimensional attention (tapped by the Stroop task) engage separate processes of visual selection, both of which are needed in normal attention processing.

Selective attention enables the prioritization of resources for processing the most salient and consequential portions of visual input. Are these portions regions or objects in space (hence the need for spatial attention) or attributes of a single object (hence the need for dimensional attention)? Both possibilities have been considered in the literature, without much crosstalk between the pertinent bodies of research. The notion of visual field or space is vital in the first approach. Attention parses the visual field (initially) into well-processed and less well-processed chunks, the parsing governed by physical proximity (as space-based models hold) or by shared figural, temporal, or other physical features (as object-based models hold). The divide between space-based accounts and objectbased accounts notwithstanding, it is important to realize that, in this approach, attention always operates on chunks of the input, and, hence, in this basic sense, it can be said to be "holistic" (cf. Goldsmith, 1998; Shalev & Algom, 2000). The notion of a "spotlight" oriented through attention (Posner, Snyder, & Davidson, 1980) has come to epitomize much-though not all-of the pertinent research.

In the second approach, by contrast, attention is an intraobject process, decomposing the stimulus into task- relevant and task-irrelevant dimensions. Because the relevant dimension must be abstracted from the whole stimulus, attention is said to be "analytic" in this approach. Note that the notion of object- or space-based selection is gratuitous in the second approach because a single object is considered (hence the absence of object-based selection) whose attributes often inhere in the same location (hence the absence of space-based selection). Attention to the word or to the color attributes of Stroop stimuli exemplifies this approach.

Are the two species of selective attention related or independent? Are both required for normal attention? If so, what is their modus operandi? In order to answer these questions, in this study we combined the two classes of attention into a single experimental design. Because Posner's orientation task (Posner, 1978, 1980; Posner & Raichle, 1994; Posner & Rothbart, 2004; Posner et al., 1980) taps spatial attention, whereas the Stroop (1935) task taps analytic intraobject attention, we expected an additive outcome when conjoining the respective manipulations. We also used a third task, the flanker task introduced by C. W. Eriksen and Hoffman (1973; see also B. A. Eriksen & Eriksen, 1974), in which the observer makes a speeded response to a central letter while attempting to ignore nearby letters- flankers-that are or are not associated with the required response. Because the Posner and the flanker tasks both entail a significant spatial component, we expected the respective manipulations to interact. Together, the Posner- Stroop combination, on one hand, and the Posner-flanker combination, on the other hand, enable a principled dissociation of the two classes of selective attention.

Posner's orientating task, on one hand, and the Stroop task, on the other hand, map onto different attentional systems. …

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