Feature-based attention: it is all bottom-up priming

Abstract

Feature-based attention (FBA) enhances the representation of image characteristics throughout the visual field, a mechanism that is particularly useful when searching for a specific stimulus feature. Even though most theories of visual search implicitly or explicitly assume that FBA is under top-down control, we argue that the role of top-down processing in FBA may be limited. Our review of the literature indicates that all behavioural and neuro-imaging studies investigating FBA suffer from the shortcoming that they cannot rule out an effect of priming. The mere attending to a feature enhances the mandatory processing of that feature across the visual field, an effect that is likely to occur in an automatic, bottom-up way. Studies that have investigated the feasibility of FBA by means of cueing paradigms suggest that the role of top-down processing in FBA is limited (e.g. prepare for red). Instead, the actual processing of the stimulus is needed to cause the mandatory tuning of responses throughout the visual field. We conclude that it is likely that all FBA effects reported previously are the result of bottom-up priming.

Keywords: feature-based attention; priming, top-down control; selective attention.

Figure 1.

Stimuli and adapted from Theeuwes et al. [63]. The cue indicated with a validity of 83% the likely target singleton dimension for the upcoming trial (the word cue ‘shape’, ‘colour’ or ‘neutral’). Observers responded to the orientation of the line segment inside the singleton which was either a pop-out red circle or a pop-out green diamond. The RT data show that observers were faster to respond to the colour singleton than to the shape singleton. Importantly, however, the validity of the cue had no effect on responding. These data indicate that top-down FBA is not effective in guiding search.

Figure 2.

(a) Observers were asked to search for one of two colour singletons and respond to the line segment inside the one that was indicated by the cue (in this example: search for the green singleton). (b) Perfect selection: observers direct attention only to the green singleton and respond to the line segment. (c) Attention is captured by the red irrelevant singleton, the line inside the irrelevant distractor singleton could be congruent (e.g. both vertical) or incongruent (e.g. one horizontal and one vertical) with the orientation of the line segment inside the (cued) target singleton. If a congruency effect is found, one can only conclude that at some point attention was directed to the irrelevant singleton (adapted from [61]).

Figure 3.

Data from J. Theeuwes & E. van der Burg (2011, unpublished data). Observers had to either search consistently for a red or green singleton (repetition condition) or consistently switch between red and green (switch condition). In the repeat condition, selection was perfect; in the repeat condition there was a significant congruency effect, suggesting that observers were not able to switch their search set from red to green and vice versa, even though they knew they had to switch from red to green, to red, to green, and so on, during the whole experiment.

Figure 4.

Observers were asked to search for one of two colour singletons and respond to the line segment inside the one that was indicated by the cue (in this example: search for the colour singleton). In this particular task, observers are able to select the circle indicated by the cue without any interference of the irrelevant distractor (adapted from [61]).