Figure 1.

Experiment protocol for the (A) isometric handgrip task that was used to modulate tonic arousal and (B) the auditory oddball task that was used to assess salience detection. During the isometric handgrip task, participants squeezed (or, in the control group, just held) an exercise ball for 18s when a blue circle appeared and then rested for 60 seconds when a yellow circle appeared. There were 5 squeeze-rest cycles in total. Approximately 6–7 minutes after the beginning of the handgrip task, participants performed an oddball task in which infrequent high-pitched oddball tones (10% of trials), infrequent novel sounds (10% of trials), and frequent low-frequency tones (80% of trials) were presented in succession. Participants had to respond as quickly as possible via button press when they heard the oddball tone, but refrain from responding when they heard the novel and standard tones.