Guided Visual Search is associated with a feature-based priority map in early visual cortex

Visual search models have long emphasised that task-relevant items must be prioritised for optimal performance. While it is known that search efficiency also benefits from active distractor inhibition, the underlying neuronal mechanisms are debated. Here, we used MEG in combination with Rapid Invisible Frequency Tagging (RIFT) to probe how neuronal excitability in early visual cortex is modulated during feature-guided visual search. Participants were instructed to indicate the presence or absence of a letter "T" presented amongst 16 and 32 "L"s. In the guided search condition, participants were informed about the colour of the "T" and could infer the colour of the irrelevant distractors. In the unguided search condition, the target colour was unknown. We found that guided search was associated with enhanced RIFT responses to the target colour, and decreased responses to the distractor colour compared to unguided search. These results conceptually replicated using both a conventional coherence approach, as well as with a General Linear Model approach based on a single-trial measure of the RIFT response. The present findings expand on previous reports based on electrophysiology and fMRI in humans and non-human primates by revealing that feature-guidance in visual search affects neuronal excitability as early as primary visual cortex.