Spatial Attention and Session Day Independently Modulate Human Visual Cortical Plasticity

Stimulus-specific response potentiation (SSRP) is a noninvasive form of cortical neuroplasticity elicited by repeated presentation of high-contrast visual stimuli. Analogous to long-term potentiation, SSRP has been proposed to exhibit input specificity, with potentiation confined to neural populations driven by the induction stimulus. In rodent models, SSRP effects accumulate across days; however, it remains unclear whether selective attention influences the magnitude or specificity of potentiation in humans. Here, we examined whether covert spatial attention modulates SSRP strength using high-density electroencephalography (EEG) in neurotypical adults. An established SSRP paradigm was modified to include an attention task during induction. Pre- and post-induction amplitudes were measured using frequency-tagged (6 and 7.5 reversals/s) bilateral hemifield contrast-sweep checkerboard steady-state visual evoked potentials (SSVEPs). The 10-minute, high-contrast, 2 Hz sign-reversing induction stimulus was presented exclusively to the left hemifield, with the right serving as control. Across two experimental sessions, participants attended either toward or away from the potentiated hemifield during induction. SSRP produced increased post-induction amplitudes in both hemifields, challenging the notion of strict input specificity. Potentiation was significantly greater on the second session day, independent of attention condition. Notably, attention enhanced SSRP in naive but not experienced observers, reflecting a significant interaction between attention and session day. Together, these findings suggest that (1) human SSRP may not be strictly stimulus-specific, (2) attention modestly enhances SSRP during initial exposure, and (3) repeated induction produces a robust plasticity effect that occludes attentional modulation.