74 CHAPTER 4 Behavioural results Reaction times Overall, NA patients were slower than healthy participants when judging the laterality of hand drawings (significant main effect of GROUP: F(1, 60) = 6.79, p < 0.0125, part. η2 = 0.10; NA: 1317ms, healthy: 1153ms) (Figure 2A). Both patients and healthy participants were faster with their right hand compared to the left hand (significant main effect of LATERALITY: F(1, 60) = 12.46, p < 0.01, part. η2 = 0.17; right: 1226ms, left: 1285ms). Moreover, both groups were slower for laterally oriented hands (complex), compared to medially oriented hands (easy) (main effect of BIOMECHANICAL COMPLEXITY: F(1, 60) = 104.60, p < 0.001, part. η2 = 0.64; complex: 1323ms, easy: 1203ms) (Figure 2B). This shows that participants were sensitive to the biomechanical constraints associated with task-related upper limb movements. 21, 25, 29, 58, 86 Furthermore, both groups were slower for stimuli with a view incongruent with the posture of their own limb, compared to congruent stimuli (main effect of POSTURE: F(1, 60) = 25.15, p < 0.001, part. η2 = 0.30; incongruent:1279ms, congruent: 1236ms) (Figure 2C). This postural effect confirms that participants incorporated the posture of their own body when performing the task. 58, 69, 70 Neither the effect of biomechanical complexity, nor the effect of posture differed between groups or per laterality (F(1, 60) < 1.30, p ≥ 0.27, part. η2 ≤ 0.02). Error rates Low overall ER showed that participants in both groups performed the task well (mean ± standard deviation, NA patients: 5.5% ± 4.2%; healthy participants 4.4% ± 3.4%; no effect of GROUP: F(1, 60) = 0.33, p = 0.57, part. η2 = 0.01) (Figure 2D). ER was similar for left and right hands (no effect of LATERALITY: F(1, 60) = 0.48, p = 0.49, part. η2 = 0.001), and this did not differ between groups F(1, 60) < 3.12, p > 0.08, part. η2 < 0.05). Neither the biomechanical complexity, nor the postural congruency of the stimuli influenced ER (F(1, 60) ≤ 0.50, p ≥ 0.48, part. η2 ≤ 0.008). Cerebral activity Shared cerebral activity across groups The task evoked brain activity related to biomechanical complexity (complex > easy) in a fronto-parieto-occipital network, including the superior parietal lobule, pre- and postcentral gyrus, superior/middle frontal gyrus, supplementary motor area, inferior/ superior lateral occipital cortex, orbitofrontal/insular cortex, thalamus and cerebellum of both hemispheres (Figure 3A, Table 2). We also found brain activity related to the participants’ own arm posture: if incongruent with the presented stimulus (incongruent > congruent), activity increased in the left precentral gyrus and the right cerebellum. The opposite contrast (congruent > incongruent) was also associated with cerebral activity in the postcentral gyrus, premotor cortex, parietal lobule and superior lateral occipital cortex (see Supplementary Table 2).These findings confirm that both primary somatomotor and visuomotor systems were involved. Finally, we observed brain activity related to the laterality of the stimulus, i.e. activity in a lateralised motor network (contralateral sensorimotor cortex, putamen and thalamus; ipsilateral cerebellum, see Figure 3B, Table 2). This pattern of activity likely represents the lateralized foot response for each stimulus.