The influence of prism adaptation on spatial biases is not dependent on which hand is used to adapt.

Rightward prism adaptation (PA) can help reduce the symptoms of spatial neglect—a disorder in which patients are unable to attend to people or objects on their left side. During rightward PA, when a patient reaches toward a target, they miss far to the right, because of the rightward visual shift. The patient must adjust their movements leftward (i.e., towards the neglected field) to compensate, which can lead to a reduction in neglect symptoms. Interestingly, previous research suggests that leftward PA can induce “neglect-like” behaviour in healthy adults as they need to adjust their movements rightward to compensate. Recent research has demonstrated a “congruency effect” wherein there is a larger magnitude of prism aftereffects when the hand used and the direction of prism shift are the same, or congruent, (e.g., left hand-left prisms) compared to incongruent (e.g., right hand-left prisms). In the present study, we examined whether the “congruency effect” would also result in a larger rightward shift in attention in healthy adults following leftward PA. To examine this, healthy adults (n = 52) completed line bisection and landmark tasks before and after leftward PA using either their left (congruent) or right (incongruent) hand across two different testing sessions. Straight-ahead pointing and washout pointing demonstrated a congruency effect, with a larger magnitude of prism aftereffect when the hand and prism shift were the same. The landmark and line bisection results also demonstrated a significant rightward shift in attention following leftward PA, but there were no significant congruency effects. These findings suggest that, while the congruency effect can influence the magnitude of adaptation aftereffects, it may not differentially influence measures of attention or spatial biases.