Figure 10.

Relationship of the NV to natural RT variability. A, A prediction of how RT might relate to firing rate given the optimal-subspace hypothesis. The shaded area represents the optimal subspace for the movement being prepared, as in Figure 1. Each dot corresponds to one trial and represents the configuration of firing rates at the time of the go cue. For some trials, that configuration may lie within the optimal subspace (green dots), leading to a short RT. For other trials, the configuration may lie outside (red dots), leading to a longer RT. B, Red and green traces show the NV, around the time of the go cue, for trials with RTs longer and shorter than the median. Traces at bottom show the mean percentage difference (short − long, ±SE) in the NV (black) and mean firing rate (blue). Data were pooled across the recordings from 7 d (monkey G), including all trials with delay periods >200 ms. C, Summary, across three monkeys and four temporal epochs, of the difference in the NV for short and long RT trials. Error bars show SEs. Filled symbols represent values significantly different from 0 (two-tailed t test, p < 0.05). The four epochs are as follows: (1) 250–50 ms before target onset, (2) the delay, (3) the 200 ms after the go cue, and (4) the 200 ms preceding movement onset. The delay epoch extended backwards from the go cue over a period equal to the minimum delay: 200, 400, and 500 ms for monkeys G, A, and B. D, Same as in B but for trials with a 30 ms delay period. Data are for monkey G and are pooled across both days that this experiment was performed.