Abstract
Goal-directed reaches performed with limb vision are more accurate and less variable than their limb occluded counterparts: a finding attributed to the increased use of continuous feedback for online limb adjustments. Moreover, recent electroencephalographic (EEG) evidence indicates that the P300 represents a cortical potential providing a relational index of online limb control. In the present study, EEG waveforms and the behavioural components of reaches were examined using a double-step paradigm wherein responses were performed with and without continuous limb vision. Notably, in advance of each trial, participants were informed of whether or not vision of their limb would be available during the response. Results showed a significant EEG amplitude difference at visual and frontal electrode sites from approximately 200-300 ms after the participant was made aware of the availability of limb vision. Additionally, differences in waveforms were related to absolute differences in the extent reach trajectories were controlled. Specifically, detailed analyses of the movement trajectories revealed increased online control for limb visible trials when compared to limb occluded conditions. Thus, differences in cortical activation prior to movement onset between limb conditions may index distinct pre-movement recruitment of cortical areas responsible for presetting the motor system to adopt a specific mode of trajectory control.
