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Group mean visual evoked potentials (VEPs) recorded during baseline placebo (BP), baseline caffeine (BC), placebo (DP) and caffeine (DC) conditions (left). The dotted vertical line marks stimulus presentation time. The scalp map for the grand-average VEP (right). The time point shown is at the peak of the VEP for the participants performing the visual task (latency 114 ms). The magnitude is indicated by the colour-bar scale at the bottom.
