While final angular size was not always a strong predictor of the occurrence of cocontraction (Figures S4A and S4B), the probability distribution of the DCMD maximum firing rate for trials with cocontraction was shifted to larger firing rates compared to trials without cocontraction (Figure 6B). Using a linear discriminant, we could predict with an accuracy of 83% the occurrence

of cocontraction based on whether the maximum DCMD firing rate exceeded 248 spike [spk]/s (Figure S4C). Second, in a subset of these trials (nT = 9, nL = 6) only one or two extensor spikes were recorded after the stimulus had stopped and the DCMD had reached its maximum activity (Figure S4D). Thus, the maximum DCMD activity this website in these trials, 300 spk/s on average, was just above the

threshold required Inhibitor Library concentration to trigger the cocontraction (SD: 72). This value is close to that suggested to trigger collision avoidance in flight (Santer et al., 2006) and not significantly higher than that estimated with a linear discriminant (t test, p = 0.073). Furthermore, in these trials the average delay between the maximum DCMD firing rate and the start cocontraction was 36 ms (SD: 23). As a third approach for assessing the role of a DCMD firing rate threshold in triggering cocontraction, we carried out a correlation analysis on the data recorded in trials with full stimulus expansion. We hypothesized that if the cocontraction is triggered when a fixed delay has elapsed following a threshold DCMD firing rate, the value of the firing rate at that delay must be independent of l/|v|. Consistent with this hypothesis, the DCMD firing rate and the stimulus size to speed ratio were uncorrelated 40 ms prior to cocontraction onset (Figure 6C). The firing rate at this delay did not significantly change with l/|v| (pKWT = 0.6) and had an average of 225 spk/s (SD: 73; Figure 6D), Bay 11-7085 close to the values predicted by the two other methods considered above. Taking into account

the observed variability, we conclude that the cocontraction is triggered approximately 40 ms after the DCMD approximately exceeds a firing rate of 250 spk/s. Using data from the same experiments, we next checked that the total number of DCMD spikes from trial start to cocontraction onset was only weakly correlated with the time of cocontraction (ρ = 0.07, p = 0.6). This result is also consistent with a change in DCMD firing rate immediately before cocontraction onset, such as a firing rate threshold, being more critical than accumulation of spikes over the entire trial. The trial-by-trial correlation of the firing rate threshold time with that of cocontraction onset was high (ρ = 0.6, p < 10−9; Figure S4E) and predicted 36% of the variance of cocontraction onset. Furthermore, this correlation value decreased by 1/3 when we randomly shuffled these two variables across trials (ρ = 0.39, p = 0.01; mean over 100 shuffles, SD: 0.