Terminal, but not concurrent prism exposure produces perceptual aftereffects in healthy young adults.

A short period of prism adaptation (PA) has been shown to reduce spatial neglect symptoms. Recent evidence suggests that the positive effects of PA might be restricted to visually guided actions, with PA having little effect on perception. However, the majority of studies have adopted a concurrent exposure technique that fosters the development of a change in felt arm position (proprioceptive straight ahead, PSA). Few studies have used terminal exposure that promotes a change in the perceived visual direction (visual straight ahead, VSA). The positive effects of PA might appear to be primarily action based because studies have adopted an exposure technique that promotes a change in proprioception. Here, we compare the effects of the two exposure types on a perceptual and a manual line bisection task in healthy young adults. Before and after seven minutes of exposure to leftward displacing prisms we measured performance on two line bisection tasks (manual and perceptual) and perceived straight ahead (PSA and VSA). During the exposure period participants made pointing movements while the view of their pointing arm was either (i) restricted to the second half of the pointing movement (concurrent exposure) or (ii) restricted to the final part of the pointing movement (terminal exposure). In line with the previous research, concurrent exposure produced a large shift in PSA and a shift on the manual line bisection task. Interestingly, terminal exposure produced a large shift in VSA and a shift in performance on the perceptual line bisection task. Our results shed light on the underlying mechanisms of prism-induced neglect recovery and help to address an apparent discrepancy within the literature.