Too alert to think straight: combined neurophysiological and modeling evidence of impaired internal shielding during hypervigilance

Hypervigilance refers to heightened sensitivity to the environment in an effort to detect potential threats. While it is known to enhance external attention, its effects on internal attention—and more critically, the attentional balance between external and internal attention—remain unclear. To investigate the underlying neurophysiological mechanisms, we recorded EEG and eye fixations from 46 participants performing the Switching Attention Task (SAT) while hypervigilance was induced. In the SAT, participants completed a discrimination task based on either visual perception or memory, with trials requiring repetition within an attention type or switches between them. In the experimental condition, hypervigilance was induced during the SAT through a task-unrelated aversive sound played unpredictably. Skin conductance, subjective ratings, and eye fixation data confirmed successful induction of hypervigilance. At the behavioral level, using a drift diffusion model, we found that hypervigilance selectively impaired the shielding efficiency of internal attention by reducing drift rate during internal repetition. EEG results showed that this impairment was captured by changes in the target-locked P2 component, underscoring its role in internal shielding. A joint modeling approach further revealed that the association between drift rate and P2 was altered under hypervigilance during internal repetition, confirming the impairment of internal shielding under hypervigilance. Additionally, we observed a subtle change in the relationship between N1 and drift rate during external trials, suggesting possible facilitation. Together, these findings offer novel insights into how hypervigilance modulates attentional balance.