The Role of the Caudal Superior Parietal Lobule in Updating Hand Location in Peripheral Vision: Further Evidence from Optic Ataxia

Abstract

Patients with optic ataxia (OA), who are missing the caudal portion of their superior parietal lobule (SPL), have difficulty performing visually-guided reaches towards extra-foveal targets. Such gaze and hand decoupling also occurs in commonly performed non-standard visuomotor transformations such as the use of a computer mouse. In this study, we test two unilateral OA patients in conditions of 1) a change in the physical location of the visual stimulus relative to the plane of the limb movement, 2) a cue that signals a required limb movement 180° opposite to the cued visual target location, or 3) both of these situations combined. In these non-standard visuomotor transformations, the OA deficit is not observed as the well-documented field-dependent misreach. Instead, OA patients make additional eye movements to update hand and goal location during motor execution in order to complete these slow movements. Overall, the OA patients struggled when having to guide centrifugal movements in peripheral vision, even when they were instructed from visual stimuli that could be foveated. We propose that an intact caudal SPL is crucial for any visuomotor control that involves updating ongoing hand location in space without foveating it, i.e. from peripheral vision, proprioceptive or predictive information.

Eye-Hand Coordination during Visuomotor Adaptation with Different Rotation Angles: Effects of Terminal Visual Feedback

“…Furthermore, unlike prism adaptation studies, the current study used a tool-use setting where visual targets and visual feedback were displayed on the vertical plane and hand movements were made on the horizontal plane, thereby requiring an additional coordinate transformation to link the hand and visual information [39]. Different visuomotor processes underlying reaching between natural and tool-use settings were revealed recently [49,62,63]. Moreover, the current task required controls of both the hand’s initial trajectory direction and stopping at the target, whereas prism adaptations often require mainly the control of the hand’s initial trajectory direction, such as throwing a ball [59] or rapid pointing being mechanically stopped as the finger lands on the target [60].…”

Decoupled Visually-Guided Reaching in Optic Ataxia: Differences in Motor Control between Canonical and Non-Canonical Orientations in Space

“…Such egocentric guidance of conflicting visual and proprioceptive information in peripheral space [11,33] and online updating required following target displacement [25-27,29,30,60] are primarily affected from dorsal stream damage. This suggests that the OA deficit includes an impaired integration of conscious awareness of eye-centered metrics with transient online representations of limb-centered metrics.…”

Microstructure of the superior longitudinal fasciculus predicts stimulation-induced interference with on-line motor control

“…The rationale to define a hand trajectory as corrective or as erroneous was as follows (Fig. 2): (1) we first obtained the distribution of all the finger endpoints for the undisplaced trials by calculating the ellipsoid 95% confidence interval (CI) (Granek et al, 2012;Messier and Kalaska, 1999). Trajectories of displaced trials in which the indexfinger endpoint position was within this CI were considered as erroneous trajectories (Pisella et al, 2000).…”