Performance metrics related to initial adaptation (Adaptation 1 and 2), learning and savings over the 24 h consolidation interval, and after-effects, were evaluated using separate linear mixed effects (LME) models, with the lme4 package (Bates et al., 2015) in R version 3.2.4 (R Development Core Team, 2013). LME models are almost identical to more traditional fixed-effects ANOVA, except that they include all trials as separate observations for each participant and allow testing (and hence control) of both fixed and random (subject) effects, especially suited to RM designs (Galwey, 2006). All models were used to assess error as a function of group, time point, their interaction, and a random intercept for each participant and are reported in reference to the Act group (see Supplemental Materials for tables of LME outputs).

Separate LME models were conducted on the CE data to probe adaptation during Adaptation 1 and 2 based on the same 5 physical practice blocks which were common to all groups: blocks 2, 4, 6, 8, 10. Note there were four groups/time point as there were no data for the Obs_Pre and Post groups in Adaptation 1 and 2, respectively. To investigate savings (comparing early adaptation and delayed retention) and any gains or losses following the delayed retention interval (comparing late adaptation and 24 h retention test), a LME model test was conducted that included the first adaptation time point (first five trials where participants physically practiced), as well as Retention 1 (last 5 trials; Day 1) and Retention 2 (first 5 trials; Day 2) time points. To compare differences in after-effects, a LME model was run using Pre-test, Post-test 1, Post-test 2 and Post-test 3 as time points (all data were compared relative to pre-test). The same LME model design that was used for CE data during adaptation was applied to the VE and RT data during Adaptation 1 and 2.

Where relevant, between group differences across Adaptation and Retention tests were followed up with Tukey's HSD post-hoc tests, using the multcomp package in R (Bretz et al., 2016). Effect sizes (Cohen's d; Cohen, 1988) were included to characterize the magnitude of forgetting between Retention 1 and Retention 2 (as errors were shown to increase), savings from Adaptation 1 to Retention 2, and the magnitude of after-effects calculated as the difference between pre-test and each post-test (resulting in 3 separate effect sizes per group).

To establish if variability of aiming errors during Adaptation was related to subsequent after-effect magnitude, two separate omnibus post-hoc Pearson correlation coefficients were conducted. One on mean VE during Adaptation 1 and after-effect magnitude (absolute value of the mean difference in CE error between the last 5 trials of Pre-test and first 5 trials of Post-test 1; 4 groups), and a separate correlation for mean VE during during Adaptation 2 and after-effect magnitude (absolute value of the mean difference in CE error between the last 5 trials of Pre-test and first 5 trials of Post-test 2; 4 groups).

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