Financial incentives enhance adaptation to a sensorimotor transformation.

Adaptation to sensorimotor transformations has received much attention in recent years. However, the role of motivation and its relation to the implicit and explicit processes underlying adaptation has been neglected thus far. Here, we examine the influence of extrinsic motivation on adaptation to a visuomotor rotation by way of providing financial incentives for accurate movements. Participants in the experimental group "bonus" received a defined amount of money for high end-point accuracy in a visuomotor rotation task; participants in the control group "no bonus" did not receive a financial incentive. Results showed better overall adaptation to the visuomotor transformation in participants who were extrinsically motivated. However, there was no beneficial effect of financial incentives on the implicit component, as assessed by the after-effects, and on separately assessed explicit knowledge. These findings suggest that the positive influence of financial incentives on adaptation is due to a component which cannot be measured by after-effects or by our test of explicit knowledge. A likely candidate is model-free learning based on reward-prediction errors, which could be enhanced by the financial bonuses.

Cerebellar lesions alter performance monitoring on the antisaccade task--an event-related potentials study.

Error processing is associated with distinct event-related potential components (ERPs), i.e. the error-related negativity (ERN) which occurs within approximately 150 ms and is typically more pronounced than the correct-response negativity (CRN), and the error positivity (Pe) emerging from about 200 to 400 ms after an erroneous response. The short latency of the ERN suggests that the internal error monitoring system acts on rapidly available central information such as an efference copy signal rather than slower peripheral feedback. The cerebellum has been linked to an internal forward-model which enables online performance monitoring by predicting the sensory consequences of actions, most probably by making use of efference copies. In the present study it was hypothesized that the cerebellum is involved in the fast evaluation of saccadic response accuracy as reflected by the ERN. Error processing on an antisaccade task was investigated in eight patients with focal vascular lesions to the cerebellum and 22 control subjects using ERPs. While error rates were comparable between groups, saccadic reaction times (SRTs) were enhanced in the patients, and the error-correct difference waveforms showed reduced amplitudes for patients relative to controls in the ERN time window. Notably, this effect was mainly driven by an increased CRN in the patients. In the later Pe time window, the difference signal yielded higher amplitudes in patients compared to controls mainly because of smaller Pe amplitudes on correct trials in patients. The altered ERN/CRN pattern suggests that the cerebellum is critically involved in fast classification of saccadic accuracy. Largely intact performance accuracy together with increased SRTs and the altered Pe pattern may indicate a compensatory mechanism presumably related to slower, more conscious aspects of error processing in the patients.

Electrophysiological correlates of inter- and intrahemispheric saccade-related updating of visual space.

The process of spatial updating is crucial for maintaining perceptual stability despite gross and frequent displacements of space following saccadic eye movements. Efference copies of motor commands are used to update retinal coordinates across saccades. The present study investigated neural correlates of saccadic updating in a perceptual context with regard to temporal dynamics and modulation by intra- versus interhemispheric transfer of updating-related information. Twenty-two subjects engaged in a perceptual localization task which required trans-saccadic spatial updating while event-related potentials (ERPs) were recorded. In accordance with previous studies, post-saccadic perceptual localization of stimuli presented before a saccade was less accurate when relying on efference copy signals (i.e. updating was required) as compared to a control condition not involving updating. Updating-related ERP components emerged before and after saccade onset. There was no clear transfer-dependent modulation of the presaccadic component. A negative deflection between 30 and 70 ms after saccade onset was most pronounced for rightward saccades, and when intrahemispheric transfer was required. A slower positive deflection starting about 170-230 ms after saccade onset had a shorter latency for leftward than for rightward saccades and was not modulated by transfer. In accordance with previous work, this relative positivity is thought to reflect sensory memory, whereas the earlier negative deflection can be more directly linked to the updating process itself.