Instruction Alters the Influence of Allocentric Landmarks in a Reach Task

Abstract

AbstractAllocentric landmarks have an implicit influence on aiming movements, but it is not clear how an explicit instruction (to aim relative to a landmark) influences reach accuracy and precision. Here, 12 participants performed a task with two instruction conditions (egocentricvs.allocentric), but with similar sensory and motor conditions. Participants fixated gaze near the centre of a display aligned with their right shoulder while a target stimulus briefly appeared alongside a visual landmark in one visual field. After a brief mask/memory delay the landmark then re-appeared at a different location (same or opposite visual field), creating an ego/allocentric conflict. In theegocentriccondition, participants were instructed to ignore the landmark and point towards the remembered location of the target. In theallocentriccondition, participants were instructed to remember the initial target location relative to the landmark and then reach relative to the shifted landmark (same/opposite visual field). To equalize motor execution between tasks, participants were instructed to anti-point (point to the visual field opposite to the remembered target) on 50 % of the egocentric trials. Participants were more accurate, precise, and quicker to react in the allocentric condition, especially when pointing to the opposite field. We also observed a visual field effect, where performance was worse overall in the right visual field. These results suggest that when egocentric and allocentric cues conflict, explicit use of the visual landmark provides better reach performance than reliance on noisy egocentric signals. Such instructions might aid rehabilitation when the egocentric system is compromised by disease or injury.Highlights12 participants reached to remembered targets in the presence of a visual landmarkParticipants were instructed to ignore, or point relative to, the landmarkThe landmark instruction improved reaction time, precision, and accuracyThese effects were stronger when pointing was cued toward the opposite visual fieldKnowledge of these rules might be used to enhance performance or in rehabilitation