Abstract
<jats:p>The earliest stage of visual memory is often characterized as pre-attentive, yet recent work suggests that spatial attention and pre-stimulus alpha oscillations both shape iconic memory at its onset. Whether these influences reflect a common inhibitory mechanism or contribute independently is unknown. We combined an endogenous spatial pre-cue (valid, invalid, neutral) with an analysis of pre-stimulus alpha power in a partial-report paradigm, at target-to-post-cue onset asynchronies (SOAs) of 0, 120, and 1240 ms, while recording EEG from 45 participants. Behaviorally, perceptual sensitivity (d') showed a cost-dominated signature: invalid cues impaired performance relative to both neutral and valid cues at the 0 and 120 ms SOAs, with no benefit of valid over neutral cues. The pre-stimulus EEG mirrored this asymmetry: at 120 ms, stronger alpha power ipsilateral to the target predicted higher d', whereas contralateral alpha had no effect at any SOA, indicating suppression of the irrelevant hemifield rather than facilitation of the target. This ipsilateral effect was additive with cue validity rather than interactive, and it persisted in neutral trials without any directional cue. Iconic memory is thus continuously biased by the inhibitory state of early visual cortex, to which endogenous attention and spontaneous excitability fluctuations contribute through separable channels.</jats:p>