Neural Timeline of Contextual Guidance in Naturalistic Visual Search Across Task Difficulty Levels

Visual search is extremely critical in the real world and is modulated by contextual guidance. Extensive research highlights the role of contextual manipulation in enhancing visual search performance. However, the neural timeline underlying contextual guidance during ecologically valid visual search tasks remains largely unresolved. The current study uses heterogeneous targets in naturalistic visual search to explore the role of contextual facilitation of spatial attention in visual search under varying task difficulty. We hypothesized that contextual guidance-based deployment of attention to the expected location of the target will emerge in visual search tasks even in the absence of the target and investigated the neural timeline of attentional deployment, modulated by task difficulty. We used multivariate pattern classifiers to predict coarse contextual locations from single trial electroencephalogram (EEG) signals during naturalistic visual search in the absence of targets. Participants searched for heterogeneous targets in natural images, and the target-absent images carrying information for possible target locations provided by scene context were considered for analysis. Our results demonstrate that task consistent contextual locations in natural scenes can be predicted reliably pointing to the role of contextual information guiding early deployment of spatial attention in visual search. Multivariate pattern analysis (MVPA) failed to predict the expected location using the same stimuli in a separate control EEG study when contextual information was made inconsequential. Finally, we demonstrated that for easy tasks, contextual guidance facilitation starts as early as 130-170 ms poststimulus onset, alluding to the role of task difficulty in mediating the early neural timeline of contextual guidance.