Modulation of neural activity by motivational and spatial biases.

Motivational biases and spatial attention both modulate neural activity and influence behavioural performance. The time course of motivational bias effects, as well as the relationship between motivation and attention across the time course of information processing, however, are relatively unknown. In the present study, event-related potentials (ERPs) were recorded whilst individuals performed a modified Posner task, in which cue stimuli indicated the reward stakes of a given trial and the probable spatial location of a subsequent target stimulus. Reaction times (RTs) were sensitive to motivation and to attention, with faster responses produced on valid and on rewarded trials. In addition, motivation modulated neural activity from the visual analysis of stimuli, with an earlier N1 peak for rewarded compared with non-rewarded stimuli. Effects of motivation were relatively independent from those of attention until late cognitive processing and response production, where motivation and attention interacted to enhance P300-like potentials and the lateralised readiness potential (LRP). The results suggest that multiple sources of modulatory influences may exist, with motivation and attention exerting independent influences over early stimulus and cognitive processing, followed by a late interaction allowing the construction of a comprehensive stimulus representation that contains information pertaining to both motivational and spatial expectations.