Adaptation of gaze anchoring through practice in young and older adults

During visually guided manual movements, gaze is usually fixated to a target until a pointing movement is completed to that target, showing gaze anchoring. We previously examined gaze anchoring during a two-segment eye-hand task under a low accuracy constraint. Eye movements were made to predetermined first and second targets, while hand movements were varied across two conditions: (1) stop at the first target and discontinue (HS1) and (2) stop at both the first and the second targets (HS1S2). Young adults previously broke gaze anchoring at the first target only when the second pointing was excluded (HS1). However, older adults did not break gaze anchoring for either condition. The present study further investigated whether young and older adults break gaze anchoring through short-term practice under the same conditions. An HS1 practice proceeded to an HS1S2 practice. The results showed that the timing of terminating gaze anchoring relative to pointing completion oscillated considerably during the HS1 practice until it was stabilized. Conversely, that timing was stable during the HS1S2 practice. Nevertheless, the young adults benefited from the HS1 practice and broke gaze anchoring even when the second pointing was included in HS1S2. This indicates that gaze anchoring to pointing completion is not a prerequisite for the production of subsequent pointing. By contrast, older adults did not improve the timing of gaze anchoring termination for either practice condition, thereby failing to break gaze anchoring. Thus, aging compromises a predictive control of terminating gaze anchoring relative to pointing completion, which is difficult to overcome through short-term practice.