Visuomotor adaptation and proprioceptive recalibration in older adults

Abstract

Previous studies have shown that both young and older subjects adapt their reaches in response to a visuomotor distortion. It has been suggested that one's continued ability to adapt to a visuomotor distortion with advancing age is due to the preservation of implicit learning mechanisms, where implicit learning mechanisms include processes that realign sensory inputs (i.e. shift one's felt hand position to match the visual representation). The present study examined this proposal by determining if changes in sense of felt hand position (i.e. proprioceptive recalibration) follow visuomotor adaptation in older subjects. As well, we examined the influence of age on proprioceptive recalibration by comparing young and older subjects' estimates of the position at which they felt their hand was aligned with a visual reference marker before and after aiming with a misaligned cursor that was gradually rotated 30 degrees clockwise of the actual hand location. On estimation trials, subjects moved their hand along a robot-generated constrained pathway. At the end of the movement, a reference marker appeared and subjects indicated if their hand was left or right of the marker. Results indicated that all subjects adapted their reaches at a similar rate and to the same extent across the reaching trials. More importantly, we found that both young and older subjects recalibrated proprioception, such that they felt their hand was aligned with a reference marker when it was approximately 6 degrees more left (or counterclockwise) of the marker following reaches with a rotated cursor. The leftward shift in both young and older subjects' estimates was in the same direction and a third of the extent of adapted movement. Given that the changes in the estimate of felt hand position were only a fraction of the changes observed in the reaching movements, it is unlikely that sensory recalibration was the only source driving changes in reaches. Thus, we propose that proprioceptive recalibration combines with adapted sensorimotor mappings to produce changes in reaching movements. From the results of the present study, it is clear that changes in both sensory and motor systems are possible in older adults and could contribute to the preserved visuomotor adaptation.

Vision and proprioception in action monitoring by young and older adults

“…That is, we found an age-related decline in the capability to discriminate the input and the output of a visuo-motor transformation. This finding is in line with a tentative result of our recent study (Wang et al, 2012) as well as with a rather incidental observation in a recent adaptation study in which rotated visual feedback was displayed in the plane of the hand movements rather than on a monitor placed in front of the workspace of the hand (Cressman et al, 2010). The agerelated decline of inter-modal discrimination can account for the poorer adaptation of older adults to visuo-motor rotation, in particular with respect to explicit knowledge (Bock, 2005;Heuer and Hegele, 2008;Heuer et al, in press).…”

How does ageing affect grasp adaptation to a visual–haptic size conflict?

“…These findings appear to support some of the previous adaptation studies which have also shown similar levels of adaptation between young and older adults (Canavan et al 1990; Etnier and Landers 1998; Roller et al 2002; Bock and Schneider 2002; Buch et al 2003; Cressman et al 2010). There are several explanations for these results, which are not necessarily mutually exclusive.…”

“…time taken to re-adapt) may be positively correlated with the initial amount of adaptation that occurred, and so has been used as an indicator of the strength of adaptation (Fernández-Ruiz and Díaz 1999). While adaptation may rely on both internal models and strategic control mechanisms, this re-adaptation is almost exclusively governed by internal models to correct the movement, since strategic control mechanisms dissipate quickly in the absence of a sensorimotor discrepancy (Redding and Wallace 1996; McNay and Willingham 1998; Bock 2005; Bock and Girgenrath 2006; Cressman et al 2010). Similar to these traditional models of adaptation, it has also been shown that the rate of motor adaptation can be predicted using a Bayesian learner model which optimally combines knowledge and belief (i.e.…”

Retention of proprioceptive recalibration following visuomotor adaptation

“…When tested the following day, subjects showed perfect retention (99.6% retained) of this shift in felt hand position. However, given the smaller magnitude following adaptation compared to our previous papers (~6° change with a 30° distortion) (Cressman and Henriques 2009;Cressman and Henriques 2010b;Cressman et al 2010;Salomonczyk et al 2011), we investigated further and noticed a group of subjects who did not show a shift in the expected direction following training with a visuomotor discrepancy (Fig. 4d, grey circles), despite having equivalent slopes (or uncertainty ranges) as the others, confirming correct performance of the task.…”

“…For instance, in our previous studies that had weaved reach training trials throughout proprioceptive estimates, approximately 83 to 100% of subjects showed the expected shift in sense of hand position (Cressman and Henriques 2009;Cressman and Henriques 2010b;Cressman et al 2010;Salomonczyk et al 2011;Salomonczyk et al 2012;Clayton et al 2013), whereas in those that had not (Salomonczyk et al 2013;Mostafa et al 2014), only 72 to 91% of subjects showed this recalibration.…”