Feature-based dynamics in visual search: Shifting the focus from target/distractor processing to the processing of non-target filler stimuli in the search display

• Applicant: Dr. Norman Forschack
• Subject Area: General, Cognitive and Mathematical Psychology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 535622746

Finding target objects among irrelevant and potentially distracting stimuli has been studied for decades. In visual search, there is a long-standing controversy about whether attention is captured by all salient stimuli regardless of their relevance or whether the initial allocation of attentional resources might be shaped by goal-directed search. A prominent hypothesis suggests that singletons, i.e., distractors standing out in at least one feature (e.g., color), can be suppressed and benefit the search for the target instead of diminishing search performance. Previous studies supported that view not only by behavioral data but also reported event-related potentials (ERPs) that are specific to the target (e.g., the N2pc) and the singleton (the Pd) during electroencephalographic (EEG) recordings. However, the processing of other task-irrelevant and supposedly non-salient filler stimuli that might accompany the target and singleton object were scarcely the focus of research, partly due to the limitation of the ERP technique to measure attentional allocation to the filler and target/singleton items simultaneously.Nevertheless, there is behavioral evidence that filler processing is facilitated the more similar the filler color is to the target’s color. This spread of attentional resources across visual objects sharing similar features is the main mechanism of feature-based attention (FBA). Given that fillers share at least one common feature of the target stimulus in many search displays, the role of FBA needs to be investigated for a better understanding of the spread of attentional resources across the display. In particular, when fillers are seen as a “neutral” baseline to calculate behavioral costs or benefits for presenting an additional singleton distractor, it is important to consider feature-based facilitation. The proposed project will investigate how the effects of FBA influence attentional priority in visual search designs and specifically under which conditions feature-based attentional spread to filler stimuli takes effect. We hypothesize that feature spread requires a certain exposure time with the target feature, enough processing resources, and might interact with low-level stimulus characteristics like stimulus contrast. For this, eight EEG experiments are proposed that will combine behavioral measures of distractor interference with the steady-state visual evoked potential technique, which allows measuring the attentional modulation of simultaneously presented target, singleton, and filler items. The results will inform our understanding of the neural processes underlying the deployment of attention and how FBA may shape our behavior during visual search.

• DFG Programme: Research Grants