Spontaneous alpha-band lateralization extends persistence of visual information in iconic memory by modulating cortical excitability

Pre-stimulus alpha oscillations in the visual cortex modulate neuronal excitability, influencing sensory processing and decision-making. While this relationship has been demonstrated mostly in detection tasks with low-visibility stimuli, interpretations of such effects can be ambiguous due to biases, making it difficult to clearly distinguish between perception-related and decision-related effects. In this study, we investigated how spontaneous fluctuations in pre-stimulus alpha power affect iconic memory, a high-capacity, ultra-short visual memory store. Data from 49 healthy adults (34 female and 15 male) was analyzed. We employed a partial report task, where a brief display of six stimuli was followed by a report cue indicating the target stimulus. In this paradigm, accuracy at short stimulus-cue onset asynchronies (SOAs) is typically high, reflecting the initial availability of sensory information, but it rapidly declines at intermediate SOAs due to the decay of the iconic memory trace, stabilizing at a low asymptote at long SOAs, representing the limited capacity of short-term memory. Crucially, performance in this task is constrained by the temporal persistence of sensory information, not by low visibility or response bias. We found that strong pre-stimulus alpha power enhanced performance by amplifying initial stimulus availability without affecting the speed of iconic decay. This effect was driven predominantly by stronger pre-stimulus alpha power in the hemisphere ipsilateral to the to-be-reported target, likely suppressing neuronal excitability of neurons coding irrelevant stimuli. Our findings underscore the role of alpha oscillations in modulating neuronal excitability and visual perception, independent of decision-making strategies implicated in prior studies.