Figure 2.

Quantification of behavioral and neural drift. a, Mean-subtracted speed for reaches to a single target during one experimental session (monkey E); the black trace shows the best polynomial fit of drift (Eq. 4). b, Breakdown of macaque reach speed variability for each session target into drift and residual components, expressed as SDs for both monkeys. Solid points indicate session targets with significant (p < 0.05, permutation test) drift. c–h, Analogous to a and b for initial reach direction (c, d), neural firing rate (e, f; neural firing rates were not mean subtracted, and in f, no distinction is made for cells with significant vs insignificant drift) and principal components (PC) of pitcher release point for 2011 MLB data (g, h).