Stimulus-preceding negativity and P3 reflecting relative amounts of attention allocation between primary and secondary tasks.

Objective: This study examined event-related potentials, particularly P3, in two attention states: a 'focused attention state', wherein attention was fully allocated to a primary task, and a 'poor attention state', wherein attention was disrupted by a secondary task, to elucidate attention allocation mechanisms during multitasking.

Methods: P3 was recorded under two conditions. The focus condition (focused attention state) involved only the primary task. The split-attention condition (poor attention state) included both primary and secondary tasks. Stimulus-preceding negativity (SPN) evoked by the secondary task was also recorded in the split-attention condition.

Results: P3 amplitude was significantly higher in the focus condition than in the split-attention condition. Importantly, a novel finding revealed a negative correlation between SPN amplitude for the secondary task and P3 amplitude for the primary task, suggesting a trade-off in attention allocation. Source analysis of the P3 revealed that regions associated with attention shifting and inhibitory control were active during the focus condition. In contrast, regions linked to impaired cognitive-sensory integration and increased impulsivity were prominent during the split-attention condition.

Conclusion: This study highlights a new finding: SPN and P3 amplitudes are interrelated, reflecting relative attention allocation between tasks. In poor attention states, impaired attentional shifting and inhibitory control led to reduced P3 amplitude for the primary task and heightened SPN activity for the secondary task.