Visual target distance, but not visual cursor path length produces shifts in motor behavior

Temporal persistence of after-effects in the n-1 replication task

In line with the theory of event coding, many studies on tool use show that perceived visual and haptic information interacts with action execution. In two experiments, we investigated the temporal persistence of after-effects within an event file, and after-effects in temporally overlapping event files with the n-1 replication task. Each trial consisted of two phases: In phase 1, participants moved a cursor with a pen on a covered tablet while a gain varied the relation between hand and cursor amplitude (Experiment 1). In phase 2, participants replicated the hand amplitude of phase 1 of the previous trial without visual feedback. Any systematic over- and undershoot would be indicative for after-effects. When the cursor amplitude varied and the hand amplitude remained constant, we did not find any after-effects but adjustment of the internal model. For varying hand amplitudes, after-effects appeared in terms of a contrast and assimilation effect between temporally overlapping event files and within an event file, respectively. In Experiment 2, we confirmed that the observed pattern of over- and undershoots fully reflect assimilation/contrast due to perception-action interaction. The findings extend the current view on the temporal stability of short-term binding in sensorimotor transformation tasks: In the n-1 replication task, after-effects appeared only in trials with varying hand amplitudes. We replicated the contrast effect and assimilation effect, and the assimilation effect persisted for up to approximately 20 s.

A condition that produces sensory recalibration and abolishes multisensory integration

We examined the influence of extended exposure to a visuomotor rotation, which induces both motor adaptation and sensory recalibration, on (partial) multisensory integration in a cursor-control task. Participants adapted to a 30° (adaptation condition) or 0° (control condition) visuomotor rotation by making center-out movements to remembered targets. In subsequent test trials of sensory integration, they made center-out movements with variable visuomotor rotations and judged the position of hand or cursor at the end of these movements. Test trials were randomly embedded among twice the number of maintenance trials with 30° or 0° rotation. The biases of perceived hand (or cursor) position toward the cursor (or hand) position were measured. We found motor adaptation together with proprioceptive and visual recalibrations in the adaptation condition. Unexpectedly, multisensory integration was absent in both the adaptation and control condition. The absence stemmed from the extensive experience of constant visuomotor rotations of 30° or 0°, which probably produced highly precise predictions of the visual consequences of hand movements. The frequently confirmed predictions then dominated the estimate of the visual movement consequences, leaving no influence of the actual visuomotor rotations in the minority of test trials. Conversely, multisensory integration was present for sensed hand positions when these were indirectly assessed from movement characteristics, indicating that the relative weighting of discrepant estimates of hand position was different for motor control. The existence of a condition that abolishes multisensory integration while keeping sensory recalibration suggests that mechanisms that reduce sensory discrepancies (partly) differ between integration and recalibration.

Contrasting effects of adaptation to a visuomotor rotation on explicit and implicit measures of sensory coupling

We previously investigated sensory coupling of the sensed positions of cursor and hand in a cursor-control task and found differential characteristics of implicit and explicit measures of the bias of sensed hand position toward the position of the cursor. The present study further tested whether adaptation to a visuomotor rotation differentially affects these two measures. Participants made center-out reaching movements to remembered targets while looking at a rotated feedback cursor. After sets of practice trials with constant (adaptation condition) or random (control condition) visuomotor rotations, test trials served to assess sensory coupling. In these trials, participants judged the position of the hand at the end of the center-out movement, and the deviation of these judgments from the physical hand positions served as explicit measure of the bias of sensed hand position toward the position of the cursor, whereas the implicit measure was based on the direction of the return movement. The results showed that inter-individual variability of explicitly assessed biases of sensed hand position toward the cursor position was less in the adaptation condition than in the control condition. Conversely, no such changes were observed for the implicit measure of the bias of sensed hand position, revealing contrasting effects of adaptation on the explicit and implicit measures. These results suggest that biases of explicitly sensed hand position reflect sensory coupling of neural representations that are altered by visuomotor adaptation. In contrast, biases of implicitly sensed hand position reflect sensory coupling of neural representations that are unaffected by adaptation.