Figure 5. Coherence between the left and right SCM muscles recorded during exposure to 1.8 km h⁻¹ forward perturbations (experiment 3).

A, estimated averaged coherence between the left and right SCM muscles for the first perturbation (EMG_first; black line), habituated perturbations (EMG_hab; grey line) and combined perturbation and acoustic startle (EMG_startle; dotted dark grey line). The horizontal dotted lines represents the 95% confidence limit for the coherence estimates (black line: EMG_first; grey line: EMG_hab and EMG_startle). B, distribution of the omnibus DoC test between the EMG_first; EMG_hab and EMG_startle conditions for all frequencies. The dotted line indicates the P = 0.05 threshold for a χ² distribution with 2 degrees of freedom. C, distribution of the pair-wise post hoc DoC tests for the frequencies between 0 and 30 Hz. The dotted line indicates the P = 0.01 threshold for a χ² distribution with 1 degree of freedom. D, bar graphs showing the transformed coherency (tanh⁻¹) at the ∼14 Hz frequency for the various conditions. Note the significant difference (depicted by * in panels A, B and C) in coherence at ∼14 Hz associated with a peak in coherence for the EMG_first and EMG_startle conditions and reduction in coherence for the habituated postural responses.