Abstract
Reaching for a target implies transforming a retinal representation of the target into a body-centered frame of reference. Once the movement is initiated, it is not clear if humans need to refer again to an eye- and/or head-centered frame of reference. In this study, we perturbed these transformations using neck vibration (NV). Nineteen (19) participants performed discrete reaches towards a virtual target. The perceived influence of NV was first assessed in the dark with a single target. The main conditions involved NV applied prior to (NV-Planning) or/and during the reaching movement (NV-Online/NV-Complete) or not at all (NV-None). These 4 conditions were randomly presented 20 times each. Participants also performed 20 NV-None trials before and after the main experiment. The main dependent variable was the lateral deviation of the reaching finger during the trajectory. Following the initial analysis, two groups of participants were identifiable. The "head shift" group (i.e., head rotation bias = leftward corrections) and the "target shift" group (i.e., target shift bias = rightward corrections). Analysis of the main experimental conditions revealed that only the "head shift" group revealed larger—and super-additive—lateral endpoint biases in the NV-Complete compared to the NV-None condition. These results suggest that head- to body- centered transformations take place when preparing and executing a reaching movement, especially if head motion can be sensed.Acknowledgments: This research was supported by NSERC