(A) Rhesus monkey reaches in 3D space using his right arm, while neural activity from 192 channels are recorded from two Utah arrays surgically implanted into contralateral dorsal premotor and primary motor cortex. The monkey’s arm position in space controlled the velocity of the cursor on the screen (methods described in Even-Chen et al., 2019). (B) (Left) the layout of the 40 targets to which the monkey reaches. For each of the 40 targets, two conditions are presented in a block-wise format. In one condition (block) the target has an acceptance window of size 2 cm (cyan), and in the other the acceptance window is of size 0.75 cm (red). Within each block, the targets appear randomly. Each block contains 400 trials (10 trials per target), and each experimental session contains about 10 blocks, 5 of each condition. (Right) representative arm reaches made by the monkey for four targets 8 cm away from the center with an acceptance window size of 2 cm. (C) Histograms of movement duration (MD) for the large (2 cm) and small (0.75 cm) targets (inset shows the normalized velocity profiles). The observed difference in variance is statistically significant (p=0.0262 via two-sample F-test). The MDs to the large and small targets are 461 ± 234 ms and 661 ± 258 ms. (D) Normalized variance of the preparatory neural state for the small (0.75 cm targets, red) and large (2.00 cm targets, cyan) targets. The variance in the preparatory state is computed by first taking trial-averaged firing rates for the last 200 ms of preparation before the go-cue, performing principal components analysis, and finding the volume of the error ellipse in 3D space, which captures at least 80% of the total variance (similar to as described in Vyas et al., 2018 and Even-Chen et al., 2019). Note that we do not spike sort or assign spikes to individual neurons (Wood et al., 2004). We instead use threshold crossings (Trautmann et al., 2019). (E) Proportion of movement variability explained by preparatory variability (as described in Churchland et al., 2006a), for the small (0.75 cm targets, red) and large (2.00 cm targets, cyan) targets. In D and E the p-values are computed from one-way ANOVA.