Modulation of the Visual Attention Resource Pool during Concurrent Overt and Covert Processing: An SSVEP Study

Recent work suggests that the capacity of visual attention is not strictly fixed but can flexibly modulate when task demands grow. To test this hypothesis in an ecologically valid setting, we combined dual-frequency steady-state visual evoked potentials (SSVEP; 12 Hz central, 8 Hz peripheral) with pupillometry inside an immersive virtual-reality (VR) environment. Twenty participants performed undivided (single-target) and divided (dual-target) monitoring tasks while 64-channel Electroencephalography (EEG) and pupil diameter were recorded. Compared with the undivided visual attention condition, divided visual attention produced significantly larger overt channel SSVEP power and greater pupil dilation. These neurophysiological findings indicate a demand-driven modulation (up-regulation) of the ``visual attention resource pool'' rather than a strictly zero-sum redistribution of fixed capacity. These findings refine classical capacity models by demonstrating that attentional resources are modulated in an elastic, demand-driven manner, and highlight dual-frequency SSVEP-pupillometry as an online index of attentional load in VR. The approach is readily transferable to driving simulators and adaptive brain-computer interfaces (BCI), where real-time monitoring of attentional modulation and cognitive state is critical.