Background Visual adaptation to laterally displacing prisms has long been used to induce sensorimotor conflict in order to investigate multisensory integration.¹ When pointing toward a target viewed through lateral displacing prisms, there is an initial error in pointing, and misalignment between visual and propriceptive reference frames; but repeated trials result in adaptation, with re–alignement of vision and proprioception and accurate pointing. After removing the prisms, prism adaptation (PA) can be observed as a pointing error in the opposite direction of the prismatic shift–the adaptation after–effect. Previous work has suggested that patients optic ataxia due to lesions to the IPS utilise visual and proprioceptive information differently to healthy participants when carrying out visuo–motor calculations that allow them to reach for visual targets.²

Aims To measure the effect of IPS lesions on visual and proprioceptive recalibration during prism adpatation.

Methods Nine patients with chronic IPS lesions (4 right hemishere, 2 left hemisphere, 2 bilateral) and nine matched control participants adapted to leftwards–and rightwards–shifting prisms in separate sessions. Pre–and post–adaptation pointing movements were recorded with a magnetic tracking device using two different pointing tasks that enable the separate evaluation of visual and proprioceptive after–effects: straight ahead pointing (SAP) with the eyes closed (which measures proprioceptive shift); and open loop pointing (OLP) to a visual target with vision of the arm occluded (which is assumed to measure the additive contributions of both visual and proprioceptive realignment).

Results Whilst the adaptation after–effects of patients were similar to controls for the OLP task to a visual target, they were significantly larger than controls for the proprioceptive–dependent SAP. Moreover, in contrast to additive effects of visual and proprioceptive recallibration seen in the OLP task in controls, the adaptation after–effect was smaller in the OLP task than in the SAP task in patients.

Conclusions The larger shifts in proprioceptive realignment during PA in patients, as measured by SAP, and the loss of additive proprioceptive and visual realignment in the OLP task, suggest that parietal lesions reduce visual realignment during prism adaptation. These findings suggest that parietal cortex is necessary for visual, but not proprioceptive reliagniment during PA.