Abstract
The encoding of reaching towards targets in 3-dimensional space has been studied at behavioral level. However, the contribution of coordinate systems to movement control for dissociated reaches where eye and target positions varied both in direction and depth is not fully understood. Twelve healthy participants were tested in a memory guided task where reaching targets were presented at different depths and directions in foveal and peripheral viewing conditions. The peripheral and foveal viewing conditions consisted in three eye/hand configurations: in the constant-gaze configuration, the eyes fixated a central fixation target and the hand reached one of the peripheral reaching targets, in the constant reach configuration, the eyes fixated one of the peripheral targets and the hand reached always the central target, and in the foveal reach configuration, the fixation and reaching targets were coincident. A novel approach for behavioral data was used to define the prevalent coordinate system used by each subject and it consisted in the application of combined gradient and vector analysis. The results showed reach error patterns that are based on both eye-centered and space-centered representation: in depth more deviated towards a space-centered representation and in direction perfectly balanced between eye-centered and space-centered. We correlated the trajectory variability in eye-centered and space-centered coordinates and we found that, in direction, the variability was described by a combination of linear and non linear model and, in depth, by a significant linear model. Present data indicate that the different weights of coordinate systems found in depth and direction are correlated with the variability distribution across eye/target configurations. In particular, the non linear distribution of movement variability in direction can be related to a mixed encoding and the linear distribution in depth with a more defined spatiotopic encoding.
Meeting abstract presented at VSS 2017