An EEG study of the combined effects of top‐down and bottom‐up attentional selection under varying task difficulty

Abstract

We examined the effect of combined top‐down and bottom‐up attentional control sources, using known attention‐related EEG components that are thought to reflect target selection (N2pc) and distractor suppression (PD). We used endogenous cues (valid vs. neutral) for top‐down attentional control, and salience in the form of color singletons (either the target or a distractor) for bottom‐up attentional control in visual search. Crucially, in two experiments, the task was of increasing difficulty, reporting the orientation of a tilted target (Experiment 1), or the position of a small gap within the target among tilted non‐targets (Experiment 2). Our results showed strong cueing effects on RT and accuracy in both experiments, demonstrating a general facilitation of responses to validly cued targets. Whereas the processing of salient targets was not improved compared with non‐salient targets, the presence of a salient distractor consistently worsened performance. The N2pc and PD were only observed in trials where targets were preceded by neutral cues in Experiment 1, and for validly cued targets and salient neutrally cued targets in Experiment 2. A cueing effect was found on the PD in Experiment 1, showing an amplitude reduction in trials where the target was validly cued. These results support the idea that bottom‐up attentional allocation occurs only when top‐down allocation of attention is absent or inefficient. Therefore, these results indicate that attentional selection and suppression during visual search are both influenced by top‐down cueing and give support to theories that focus on the interaction between the two types of attention.

Integrated effects of top-down attention and statistical learning during visual search: An EEG study

“…Traditionally, the N2pc has been assumed to index the shift of covert attention toward a task-relevant, or salient, stimulus (Eimer, 1996 ; Luck & Hillyard, 1994 ), but other findings suggest that the N2pc reflects various aspect of target processing (Kiss et al, 2008 ; Theeuwes, 2010 ; Zivony et al, 2018 ). Relevant for the current study, in a recent work using a very similar task to the one used here, Rashal and colleagues ( 2022 ; Experiment 2) observed an N2pc for targets preceded by a valid endogenous cue to the target location, suggesting that the N2pc reflected attentional processes also following topdown deployment of attention to that location.…”

“…Colours were randomly chosen on a given trial, with all stimuli being drawn in the same colour. The choice for two colours, which was not essential to the present task, and which was fully counterbalanced across conditions, largely relates to earlier work of ours using the same global approach (Rashal et al, 2022 ). Within each stimulus, there was a small gap (diameter of 0.25°) of the same grey colour as the background and positioned at the upper or lower part.…”

“…Still, a recent study by van Moorselaar and Slagter ( 2019 ) found instead a reduction of N2pc amplitudes when the target appeared frequently in a certain location. In their study, however, the target competed with only one other stimulus (i.e., the distractor), making the task easier as attentional selection was quickly accomplished (see also Rashal et al, 2022 , for evidence that the N2pc is modulated by difficulty-related factors). Furthermore, statistical learning in that study was constrained to target repetitions, with the target appearing at the same location for a number of consecutive trials (4 trials) within a sequence, but that location varied across the duration of the experiment.…”

“…By looking at the CNV and P1 components, we can investigate modulations to top-down attentional orienting pre- and post-stimulus array onset. A larger CNV should emerge following a valid compared with a neutral cue, reflecting advance preparation for selecting the target stimulus (Rashal et al, 2022 ; Schevernels et al, 2014 ; Van Den Berg et al, 2014 ). Furthermore, the P1 could also be modulated by the presence or absence of a valid cue.…”

Separate and overlapping mechanisms of statistical regularities and salience processing in the occipital cortex and dorsal attention network

“…In Beffara et al (2022), the task included 100%-predictive spatial cues that were presented before the display array, so that the participants knew in advance where exactly the target would appear. Thus, the participants could strategically suppress distractors processing at the uncued locations (see also Rashal et al, 2022). In Melloni et al (2012), there were no explicit spatial cues, but in a subset of experimental runs the participants knew whether or not the search display would contain a salient item (blocked presentation of the HD, STD or SDD condition, throughout the whole run).…”