A new method for tracking the preparatory activation of target templates for visual search with high temporal precision

Dodwell, Gordon; Nako, Rebecca; Eimer, Martin · 2024 · Crossref

DOI: 10.1111/psyp.14582

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Summary

This study addresses the challenge of tracking the temporal dynamics of preparatory attentional templates in visual search. While it is established that target templates bias attention toward task-relevant features, the precise neural time course of their activation prior to search display onset has remained elusive due to limitations in previous probing methods. Prior techniques suffered from sparse temporal sampling, potential underestimation of activation due to task-irrelevant probe locations, and confounding bottom-up attentional capture from highly salient singleton probes. To resolve these issues, the authors introduce a high-definition rapid serial probe presentation paradigm (RSPP–HD) designed to monitor template activation with high temporal precision using the N2pc event-related potential (ERP) component. The experimental design involved 18 participants performing a visual search task where they identified the vertical location of a target-colored area within lateralized dot clouds. Between successive search displays, task-irrelevant probe displays consisting of randomly colored dots were presented at regular intervals. Crucially, these probes occupied the same spatial locations as the search displays and contained no salient singletons, ensuring that any attentional shift was driven solely by top-down template activation rather than bottom-up salience. The study tested three stimulus onset asynchrony (SOA) conditions for the probes: 50 ms, 100 ms, and 200 ms, allowing for varying degrees of temporal sampling density. EEG data were recorded and analyzed to detect N2pc components elicited by target-color dots in the probe displays, which serve as markers of active attentional templates. The results demonstrated that the RSPP–HD paradigm successfully tracked the transient nature of search template activation. In the 50 ms condition, probe N2pcs were reliably elicited during the final 800 ms prior to the onset of the search display, with amplitudes increasing progressively toward the end of the preparation period. Analogous temporal profiles were observed in the 100 ms and 200 ms conditions, confirming that template activation is not sustained throughout the entire inter-trial interval but emerges dynamically in anticipation of the upcoming search task. The dense sampling in the 50 ms condition allowed for a smoothed analysis that clarified the emergence and time course of these components without losing temporal resolution. These findings provide direct neural evidence for the transient and anticipatory nature of attentional template activation. By eliminating confounds related to spatial location and stimulus salience, the RSPP–HD method offers a robust tool for investigating the real-time dynamics of attentional control. This approach enables researchers to probe the content and temporal profile of top-down attentional processes with high precision, advancing the understanding of how the brain prepares for and executes visual search tasks.

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• visual search