Integrating top-down and bottom-up attention control factors: an EEG study

Abstract

Attention can be controlled by bottom-up, stimulus driven, and top-down, goal-driven sources. The current study aims to examine how the different sources are integrated, using known EEG components related to attention - N2pc and Pd. These components are thought to reflect target selection and distractor suppression, respectively. We used endogenous cues for top-down attention control and salience for bottom-up attention control in a visual search task. In Experiment 1 participants reported the orientation of a tilted target preceded by a valid or neutral cue. In Experiment 2 the task was to report the location (up or down) of a small gap within the target. On some of the trials the target appeared in a different color, rendering it salient. On the other trials, the target appeared with or without a salient distractor. Our results showed cueing effects on RT and accuracy in both experiments, demonstrating a general facilitation of responses to validly cued targets. Salient targets were not detected faster than non-salient targets, and a salient distractor worsened performance. N2pc and Pd were found only in trials where the target was preceded by a neutral cue In Experiment 1. No such cueing effects were found in Experiment 2. The lack of N2pc in the validly cued trials in Experiment 1 suggests that no further engagement of attention was required by the search or the task. The evidenced Pd following a valid cue suggests the involvement of attention in the suppression of a salient distractor. The result of Experiment 2 suggests that task demands masked the effects that would otherwise be evident.