Instructions Affect Reaction Time Variability: Evaluation by Event-Related Potentials

Abstract

Auditory change detection studies have shown that a repetition effect occurs when the response-stimulus interval is less than 500 ms. However, this response repetition effect is variable. Forty healthy young subjects were asked to respond to target stimuli pertaining to event-related potentials as quickly and accurately as possible (10% target, inter-stimulus interval: 1500 ms). Reaction time (RT) for the targets was measured with electroencephalography. RT was found to be the fastest for the second instance of repeated targets and targets that appeared after 17 or more successive non-targets (p < 0.001). The longest P3 latencies and smallest P3 amplitudes were observed for the second instance of repeated targets; conversely, the shortest P3 latencies and largest P3 amplitudes were observed for targets that appeared after 17 or more successive non-targets (p < 0.001). All target stimuli were accompanied by a – 0.9 μV baseline negative shift of the frontal scalpelectroencephalography100 ms before the upcoming stimulus, suggesting that SPN was observed after every target stimulus. The non-target stimuli immediately after target were accompanied by MMN. Therefore, we concluded that subjects prioritized instructions pertaining to quicker response than those pertaining to accuracy. That explains RTs of second instance of repeated target are one of the fastest and how mistakes occur for non-target immediately after target stimulus. Negative baseline shifts detected by electroencephalography in this variable task with target and non-target event-related potentials provide key elements in the understanding of auditory responses.