Instructing to ignore a color does not promote its suppression but its facilitation in human early visual cortex

Attentional shifts during feature-based color selection trigger a bi-phasic activation sequence in early visual cortex: rapid facilitation of the to-be-attended followed by delayed suppression of to-be-ignored color(s). Does this sequence reflect a priority bias induced by instructions "to attend" to a certain task-relevant color instead of instructions "to ignore" task-irrelevant colors? In two EEG recording sessions, we instructed 20 participants either "to attend" to two colors (explicit instruction) or "to ignore" one color (implicit instruction) out of three differently colored and flickering random-dot kinematograms (RDKs) that elicited distinct steady-state visual evoked potentials (SSVEPs), a neural marker of early visual stimulus processing. Additionally, we tracked the time course of behavioral responses as a function of explicit or implicit cueing, with a behavioral study (N = 20). SSVEP amplitudes replicated the typical pattern of early amplification and delayed suppression under explicit instruction. The implicit instruction did not invert this sequence but paradoxically resulted in rapid facilitation of the cued - but to-be-ignored - color right after cue onset, that was followed by suppression of both task-relevant colors. Behavior followed this paradoxical selection process, causing significantly slower responses for the task-relevant colors compared to the explicit instruction. Clearly, the color cue triggered rapid stimulus-driven facilitation of the RDKs in the cue color(s) that caused subsequent suppression of the other color(s), regardless of their task relevance. This shows that the amplification-suppression pattern is not biased by an instructional prioritization but rather an inherent, possibly hard-wired temporal sequence during attentional shifts in feature-based attention.