Academic journal article Attention, Perception and Psychophysics

Word Cues Affect Detection but Not Localization Responses

Academic journal article Attention, Perception and Psychophysics

Word Cues Affect Detection but Not Localization Responses

Article excerpt

Many theories assume that preknowledge of an upcoming target helps visual selection. In those theories, a top-down set can alter the salience of the target, such that attention can be deployed to the target more efficiently and responses are faster. Evidence for this account stems from visual search studies in which the identity of the upcoming target is cued in advance. In five experiments, we show that top-down knowledge affects the speed with which a singleton target can be detected but not the speed with which it can be localized. Furthermore, we show that these results are independent of the mode of responding (manual or saccadic) and are not due to a ceiling effect. Our results suggest that in singleton search, top-down information does not affect visual selection but most likely does affect response selection. We argue that such an effect is found only when information from different dimensions needs to be integrated to generate a response and that this is the case in singleton detection tasks but not in other singleton search tasks.

In everyday life, we are constantly subjected to massive visual stimulation from the environment. In order to behave in a goal-directed manner, it is important to select only relevant information from the environment, to ignore information that is irrelevant. Selection of visual information that accords with our goals is referred to as top-down control of selection. However, irrelevant but salient items can also capture our attention, such as when one sees movement in the corner of the eye and feels compelled to look at what is moving. This is called bottom-up control of selection (for reviews, see, e.g., Corbetta & Shulman, 2002; Rauschenberger, 2003; Theeuwes & Godijn, 2001).

Although there is little controversy regarding the importance of bottom-up factors such as local feature contrast in selection, there is much less consensus about how these bottom-up factors interact with top-down modulation. More precisely, it is hotly debated whether top-down control modulates the selection of salient stimuli immediately or whether top-down control affects performance only after a salient stimulus has been selected on the basis of bottom-up control.

Evidence for the former stems from studies in which the amount of information available about the target identity in singleton search tasks was manipulated (Egeth, 1977; Meeter & Theeuwes, 2006; Müller, Heller, & Ziegler, 1995; Müller, Reimann, & Krummenacher, 2003; Theeuwes & Van der Burg, 2007; Treisman, 1988). A typical finding is that search is faster when observers know the identity of the target dimension within a block of trials than when the target dimension changes from trial to trial; this is referred to as a cross-dimensional cost. Although many have argued that cross-dimensional cost may result from bottom-up priming rather than from top-down modulation (e.g., Müller et al., 2003; Theeuwes, Reimann, & Mortier, 2006), Müller et al. (2003) presented evidence that top-down knowledge does affect performance, even when bottom-up priming cannot play a crucial role. In their study, the target dimension was cued with a picture cue before each trial. When the cue indicated the upcoming target dimension, performance was better than when the cue was invalid. These results, since replicated by others (Meeter & Theeuwes, 2006; Müller & Krummenacher, 2006; Theeuwes et al., 2006, Experiment 1), were taken as strong support for top-down control in visual search (Müller et al., 2003).

However, other studies suggest that these effects are not the result of top-down guidance of attention but represent effects occurring later in time (i.e., after the target has been selected for further processing; e.g., Cohen & Magen, 1999; Mortier, Theeuwes, & Starreveld, 2005; Theeuwes et al., 2006). In these studies, the response requirements were manipulated. For example, Theeuwes et al. (2006) employed the standard visual search singleton detection task (i. …

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