Movement and perception recalibrate differently across multiple days of locomotor learning

Abstract

Learning a new movement through error-based adaptation leads to recalibration of movement and altered perception of that movement. Although presumed to be closely related, the relationship between adaptation-based motor and perceptual changes is not well understood. Here we investigated the changes in motor behavior and leg speed perception over 5 days of split-belt treadmill adaptation. We specifically wanted to know if changes in the perceptual domain would demonstrate savings-like behavior (i.e., less recalibration with more practice) and if these changes would parallel the savings observed in the motor domain. We found that the recalibration of leg speed perception decreased across days of training, indicating savings-like behavior in this domain. However, we observed that the magnitude of savings across days was different between motor and perceptual domains. These findings suggest a degree of independence between the motor and perceptual processes that occur with locomotor adaptation. NEW & NOTEWORTHY Error-based adaptation learning drives changes in movement and perception of movement. Are these changes across domains linked or simply coincidental? Here, we studied changes in movement and perception across 5 days of repeated locomotor adaptation. Savings-like behavior in the motor and perceptual domains developed with different magnitudes and over different timescales, leading us to conclude that motor and perceptual processes operate at least somewhat independently during locomotor adaptation.

Split-Belt walking induces changes in active, but not passive, perception of step length

“…Lastly, the limited washout of motor after-effects could also indicate that motor and perceptual after-effects are originated by partially distinct processes. This is supported by previous research showing that motor and perceptual effects exhibit different patterns of saving 25 and retention 11 , distinct adaptation rates 6,15 and uncorrelated amounts of adaptation 8,9,12,13 . They also exhibit different patterns of generalization to other limbs 17 or novel targets 18,19 .…”

“…It has been shown that split-belt training can correct motor deficits 31,32 and it would be interesting to determine if it also corrects perceptual deficits as well. Of note, recent work indicates that perceptual changes in the estimation of speed are reduced with repeated exposure to the split condition 25 , suggesting that similar reduction would be observed in the shifts of limb position. Thus, there might be a limited long term effect of split-belt walking on perceptual changes.…”

“…Alternatively, the shifts in position might be due to changes in how subjects perceived the environment. It is known that the perception of symmetric walking speeds is shifted following split-belt walking 16,25 . More specifically, individuals during post-adaptation perceive the fast leg to move slower and the slow leg to move faster than their actual speed.…”

“…We re-exposed individuals to either the tied condition (i.e., both legs at 1 m/s) or split condition (i.e., 1.5 m/s: 0.5 m/s) during a Re-Adaptation epoch to subsequently evaluate motor after-effects in each subject. We chose to evaluate motor after-effects following the perceptual task to avoid changes in perception due to multiple transitions between tied and split environments, which are known to alter perceptual effects 25 . The Re-Adaptation epoch lasted 300 strides to ensure individuals reached a similar steady state as in the Adaptation epoch prior to assessing motor after-effects.…”

External error attribution dampens efferent-based predictions but not proprioceptive changes in hand localization

“…Changes in afferent-based estimates of hand location seem to be a robust form of sensory plasticity, as evidenced by its relatively quick emergence (Ruttle et al, 2016), its persistence despite explicit adaptation (Modchalingam et al, 2019), and its preservation despite aging Vachon et al, 2019) and within other forms of perturbations (Cressman and Henriques, 2009;Ostry et al, 2010;Cameron et al, 2012;Leech et al, 2018;Sombric et al, 2019). Furthermore, the recalibration of proprioception is intact in people with mild cerebellar ataxia (Henriques et al, 2014), despite the cerebellum playing a crucial role in adaptation (Martin et al, 1996;Bastian, 2006;2008;Tseng et al, 2007;Synofzik et al, 2008;Taylor et al, 2010;Izawa et al, 2012;Wong et al, 2019).…”