Effects of spatial attention on iconic memory are primarily driven by costs rather than benefits

The role of spatial attention in iconic memory - an early interface between visual perception and short-term memory - remains poorly understood. Across two experiments run in 2025, we investigated how endogenous spatial attention modulates iconic memory using a partial-report paradigm. In both exper-iments, pre-cues manipulated the allocation of spatial attention before stimulus onset. Stimulus arrays were then briefly presented to one hemifield and followed by a post-cue that probed iconic memory at varying delays after stimulus offset. In Experiment 1 (N = 47), valid attentional cues improved perfor-mance at short delays. Performance was modeled with an exponential decay function to dissociate effects on initial stimulus availability at short SOAs, the rate of iconic decay, and later transfer to working mem-ory. This analysis indicated that valid pre-cues increased initial stimulus availability relative to invalid pre-cues. In Experiment 2 (N = 66), a neutral pre-cue condition was added, and post-cues were pre-sented at three delays (0, 120, and 1240 ms). This revealed that performance differences were driven by attentional costs at invalidly cued locations, with no detectable benefits at validly cued locations relative to neutral cues. Together, these results show that spatial attention modulates the earliest measurable phase of iconic memory by shaping the initial sensory trace. The cost-dominated pattern suggests that attention primarily suppresses information at unattended locations rather than enhancing representa-tions at attended locations. This finding challenges the view of iconic memory as a pre-attentive sensory store and indicates that attentional selection operates earlier than previously assumed. Significance StatementThe influence of attention on iconic memory - a high-capacity, ultra-brief sensory store - remains highly debated. We demonstrate that endogenous spatial attention modulates iconic memory at its earliest measurable stage. Critically, this modulation reflects an attentional cost at unattended locations rather than a benefit at attended locations, suggesting that spatial attention acts through inhibitory suppression of irrelevant sensory input. These findings challenge models proposing that early sensory representation is categorically attention-free and establish a suppressive role for attention in shaping visual short-term memory at its earliest stage.