Threatening stimuli influence visual attention by distracting from the task at hand and enhancing performance. However, the underlying mechanisms remain poorly understood. The arousal stimulation effect suggests that, while threats initially capture attention, high arousal levels may subsequently facilitate attentional processing. Our study investigated this proposition using a visual search paradigm alongside electrodermal activity recordings. Participants performed a number matrix search while task-irrelevant images of varying emotional intensity (neutral, medium-arousal threat and high-arousal threat) appeared in the periphery of their vision. We analysed reaction times reflecting early and sustained attentional processing, and we recorded skin conductance responses (SCRs) to gauge physiological arousal. Behavioural data revealed that medium-arousal threat images impaired overall search efficiency, whereas high-arousal threats initially slowed performance but ultimately improved continued search efficiency. Physiologically, high-arousal stimuli prompted faster and greater SCRs than medium-arousal and neutral stimuli. No notable differences in SCRs emerged between medium-arousal threat images and neutral images. These results provide direct physiological support for the arousal stimulation effect, revealing a non-linear interaction between arousal intensity and attentional function. Our work emphasises the critical roles of arousal magnitude and timing in modulating attention in response to emotional stimuli.