Supplementary Figure 3: Spinal reflexes are not influenced by volitional intent

a, Mean rectified triceps EMG activity following the mechanical perturbations that flexed the elbow and flexed the wrist (experiment 3; n = 15). Red and blue traces represent ‘counteract’ and ‘do not intervene’ blocks, respectively. Data are aligned to perturbation onset. Shading represents ± 1 s.e.m. b, Goal-dependent activity within the spinal (SR) and long-latency (LL) epochs for trials in which the mechanical perturbation flexed the elbow and flexed the wrist. Error bars represent 95% confidence internals. c, Same format as a, but for trials in which the elbow was flexed and no perturbation was applied to the wrist. d, Same format as b, but for trials in which the elbow was flexed and no perturbation was applied to the wrist. e, Same format as a, but for trials in which the mechanical perturbations flexed the elbow and extended the wrist. f, Same format as b, but for trials in which the mechanical perturbations flexed the elbow and extended the wrist. The magnitude of the triceps spinal stretch reflex was not influenced by the intended action, when the wrist was flexed, not perturbed, or extended (ts(14) all < 1.58, ps all > 0.135, all Cohen d < 0.42). In contrast, the triceps long-latency stretch reflex was influenced by the intended action, and this occurred for all three wrist perturbation conditions (ts(14) all > 4.01, ps all < 0.001, all Cohen d > 1.0: repeated measures ANOVA three-way interaction [epoch (spinal, long-latency) by wrist perturbation (flexed, neutral, extended) by volitional intent (counteract, do not intervene)] for initial omnibus test (F(2,28) = 17.19, p < 0.001, η²_partial = 0.55).