Results
CORTEX
Thirty-six healthy individuals were enrolled in this study (mean age: 24.4 ± 3.7 years; 17 males and 19 females). Four participants in the VMI group who did not experience the kinesthetic illusion (seven-point Likert scale: less than + 1 point) and three participants in the AO group who experienced the kinesthetic illusion (seven-point Likert scale: more than + 1 point) were excluded, resulting in a total of 29 included participants for analysis (VMI group: 14 participants, AO group: 15 participants). The two groups had no significant differences in basic characteristics (p > 0.05, Table Characteristics of overall participants and two group.Data are expressed as mean ± standard deviation.VMI, visual-motor illusion; AO, action observation.Regarding the improvement rate in the ball-rotation task, the group main effect (between the VMI and AO groups) was observed [F (1, 54) = 6.09, p < 0.001], and the VMI group showed significantly higher values than the AO group in both phases. The phase main effect (between improvement phases 1 and 2) was not observed [F (1, 54) = 0.47, p = 0.495], and no interaction was observed between the improvement phases and groups [F (1, 54) = 0.01, p = 0.911, Fig. The ball rotation task. Dark gray indicated the visual-motor illusion (VMI) group. Light gray indicated the action observation (AO) group. The main effect (between the VMI and AO groups) was observed [F (1, 54) = 6.09, p < 0.001], and the VMI group showed a significantly higher finding than the AO group. The phase main effect (between the improvement phases 1 and 2) did not show a significant difference [F (1, 54) = 0.47, p = 0.495], and the interaction did not show a significant difference between the improvement phases 1 and 2 [F (1, 54) = 0.01, p = 0.911].Figure Signal responses of oxygenated hemoglobin and deoxygenated hemoglobin in the significant channels. Red line indicated oxygenated hemoglobin (oxy-Hb) in pre phase. Light green line indicated deoxygenated hemoglobin (deoxy-Hb) in pre phase. Yellow line indicated oxy-Hb in post phase. Blue line indicated deoxy-Hb in post phase. Pink line indicated oxy-Hb in post 2 phase. Black line indicated deoxy-Hb in post 2 phase.Results of brain activity of both group.Data are expressed as mean ± standard deviation.VMI, visual-motor illusion; AO, action observation; Ch, channels; ROI, region of interest; DLPFC, dorsolateral prefrontal cortex; PMC, premotor cortex; p values, false discovery rate corrected.Results of brain activity of improvement phase.Data are expressed as mean ± standard deviation.VMI, visual-motor illusion; AO, action observation; Ch, channels; ROI, region of interest; DLPFC, dorsolateral prefrontal cortex; PMC, premotor cortex; Pa, parietal area; p values, false discovery rate corrected.Regarding the degree of kinesthetic illusion, Q1 was 1.75 (1  to  3) with the VMI group and − 0.5 (− 3  to  0) with the AO group. The VMI group had significantly higher scores than the AO group (Z = 8.23, p < 0.001). Regarding the degree of sense of body ownership, Q2 was 2 (1  to  3) with the VMI group and − 2 (− 3  to  1) with the AO group, and Q3 was − 2 (− 3  to  − 1) with the VMI group and 2 (− 1  to  3) with the AO group. The VMI group had significantly higher scores than the AO group (Q2: Z = − 4.40, p < 0.001; Q3: Z = 4.40, p < 0.001). Q4 was − 2 (− 3  to  − 1) with the VMI group and − 1 (− 3  to  1) with the AO group, and there were no significant differences between the two groups (Z = 1.37, p > 0.05). Regarding the degree of sense of agency, Q5 was 2 (1  to  3) with the VMI group and − 1 (− 3  to  3) with the AO group, and Q6 was − 1.5 (− 3  to  − 3) with the VMI group and 1 (− 3  to  3) with the AO group. The VMI group had significantly higher scores than the AO group (Q5: Z = − 3.22, p < 0.001; Q6: Z = 2.62, p = 0.009).