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. 2023 Apr;85(3):685-704.
doi: 10.3758/s13414-022-02629-6. Epub 2022 Dec 16.

Attentional capture is modulated by stimulus saliency in visual search as evidenced by event-related potentials and alpha oscillations

Norman Forschack  1 , Christopher Gundlach  2 , Steven Hillyard  3 , Matthias M Müller  2
Affiliations

Attentional capture is modulated by stimulus saliency in visual search as evidenced by event-related potentials and alpha oscillations

Norman Forschack et al. Atten Percept Psychophys. 2023 Apr.

Abstract

This study used a typical four-item search display to investigate top-down control over attentional capture in an additional singleton paradigm. By manipulating target and distractor color and shape, stimulus saliency relative to the remaining items was systematically varied. One group of participants discriminated the side of a dot within a salient orange target (ST group) presented with green circles (fillers) and a green diamond distractor. A second group discriminated the side of the dot within a green diamond target presented with green circle fillers and a salient orange square distractor (SD group). Results showed faster reaction times and a shorter latency of the N2pc component in the event-related potential (ERP) to the more salient targets in the ST group. Both salient and less salient distractors elicited Pd components of equal amplitude. Behaviorally, no task interference was observed with the less salient distractor, indicating the prevention of attentional capture. However, reaction times were slower in the presence of the salient distractor, which conflicts with the hypothesis that the Pd reflects proactive distractor suppression. Contrary to recent proposals that elicitation of the Pd requires competitive interactions with a target, we found a greater Pd amplitude when the distractor was presented alone. Alpha-band amplitudes decreased during target processing (event-related desynchronization), but no significant amplitude enhancement was observed at electrodes contralateral to distractors regardless of their saliency. The results demonstrate independent neural mechanisms for target and distractor processing and support the view that top-down guidance of attention can be offset (counteracted) by relative stimulus saliency.

Keywords: Attentional capture; Cognitive and attentional control; Electrophysiology.

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Figures

Fig. 1
Fig. 1
Task design. An exemplary trial started with a fixation period of 500–1,500 ms. After that, the visual search display appeared for 100 ms. Participants discriminated as fast and accurately as possible the side of the dot within the target shape. Responses were allowed throughout the post-stimulus fixation period of 1,200 ms. Finally, a blank screen marked the end of the trial. After 550 ms, the pre-stimulus fixation period of the next trial started. The target shape was either the green diamond (SD group) or the orange square (ST group). Targets and distractors could occur together or separately at randomized locations. The remaining locations were filled with green circles (fillers)
Fig. 2
Fig. 2
Event-related current source densities contra- and ipsilateral to the non-salient green diamond target and salient orange square distractor extracted at P08 and PO7 for the conditions "target lateral - distractor vertical" (a, TLDV), "single target lateral" (b, TL), "distractor lateral - target vertical" (c, DLTV) and "single distractor lateral" (d, DL). The difference potential between contra- and ipsilateral scalp sites is given in orange for each condition. Zero marks the onset of the visual search display. Grey shaded areas indicate the three time windows used for averaging current source density (CSD) values of the lateralized potential for further statistical analysis (window 1: 144–164 ms, window 2: 202–222 ms, window 3: 251–271 ms). Insets reflect the topographical CSD distribution of the contralateral minus ipsilateral difference collapsed across left and right hemispherical electrodes (see Methods section for details) and averaged for each of the three windows
Fig. 3
Fig. 3
Event-related current source densities extracted at P07 and P08 sites contralateral and ipsilateral to the stimulus and topographic current source density (CSD) distributions of the contralateral minus ipsilateral difference for the ST group that received the salient orange square target and non-salient green diamond distractor. Other figure conventions are identical to those of Fig. 2
Fig. 4
Fig. 4
(a+c) Grand mean lateralized current source density values averaged for each group and analysis window (Win1: 144–164 ms, Win2: 202–222 ms, Win3: 251–271 ms) for conditions TLDV, TL, DLTV, and DL. Error bars indicate the 95% confidence interval of a t-test against zero. Superposition of ERP difference waves for the two different groups and averaged across both target lateral (b) and both distractor lateral (d) conditions, respectively. Line colors reflect target/distractor colors for the two groups. Difference waves are tested against zero in the time range from 130 to 300 ms relative to stimulus onset. The bold horizontal lines indicate significant lateralized potentials. The color indicates group identity. Zero marks the onset of the visual search display. ptfce<0.05; p-value threshold after correction for multiple comparisons. TLDV target lateral, distractor vertical, DLTV distractor lateral, target vertical, TL target lateral only, DL distractor lateral
Fig. 5
Fig. 5
Contra- and ipsilateral alpha source current density time courses for the SD group with a non-salient target and a salient singleton distractor, corrected by a mean prestimulus baseline between -500 and -200 ms relative to search display onset. Mean values were extracted at the symmetrical electrode clusters indicated by the purple dots of the topographical insets for the conditions "target lateral - distractor vertical" (a, TLDV), "single target lateral" (b, TL), "distractor lateral - target vertical" (c, DLTV) and "single distractor lateral" (d, DL). Topographical distributions show the difference between left and right target or distractor presentations, respectively. Colored shaded areas show within-subject confidence intervals. The difference between contralateral and ipsilateral amplitudes was compared in the time range from 400 to 800 ms relative to stimulus onset indicated by the grey boxes. Zero marks the onset of the visual search display
Fig. 6
Fig. 6
Contra- and ipsilateral alpha source current density time courses for the ST group with a salient target and a non-salient singleton distractor. Other figure conventions are the same as those in Fig. 5
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