## 4 Discussion  
The force tracking system developed in the present study can efficiently assess force control capabilities in a shorter time (about 10 min) than the force control tests used in previous studies. The force tracking system can quantify four measures of each force control phase (initiation time, development time, maintenance error, and termination time) and one overall measure (tracking error) using a single force tracking test. However, the force control tests used in previous studies [10; 11; 13; 15] quantify the four measures by  
Figure 4: Percentages of patients outside the 99% confidence intervals of the force control capabilities of the normal group (IT: initiation time, DT: development time, ME: maintenance error, TT: termination time, TE: tracking error). Figure 3: Force control capabilities of the normal, subcortical vascular mild cognitive impairment (svMCI), and subcortical vascular dementia (SVaD) groups (letters indicate statistical differences at \(\alpha=0.05\)). (**a**) Initiation time; (**b**) development time; (**c**) maintenance error; (**d**) termination time; (**e**) tracking error. separately testing each force control phase, which requires more time to complete than the force tracking test. The force tracking system can better statistically discriminate the severity of the force control deficiencies. [PERSON] et al. (2011) and [PERSON] et al. (2015) used force control tests and failed to show a significant difference in IT between the normal and svMCI groups, while this study clearly showed a significant difference. In addition, [PERSON] et al. (2011) had similar results for svMCI and SVaD in ME; however, this study showed a clear difference between the two patient groups. The present study was more sensitive because the force tracking test required more action-intention, making it easier to detect mild dysfunction in the action-intention system. However, large-scale experiments are needed using the force tracking system developed in this study to confirm these findings. Patients with SVaD showed force control capabilities in all measures worse than those with svMCI. IT (mean = 0.84 s), DT (0.89 s), ME (1.71 N), TT (1.88 p), and TE (4.33 N) in the SVaD group were 31%, 14%, 24%, 36%, and 14% greater than those (0.64 s in IT, 0.78 s in DT, 1.38 N in ME, 1.38 s in IT, and 3.80 N in TE) in the svMCI group, respectively. From these results, we conclude that SVaD patients have more severe dysfunction in the action-intention system than svMCI patients. These findings are consistent with previous studies ([PERSON] et al., 2014; [PERSON] et al., 2014) that show that svMCI may represent a prodormal state of SVaD in terms of neuropsychological results and neuroimaging findings. The proportion of patients outside the 99% confidence intervals of the force control capabilities of the normal group was higher for ME and TE in the svMCI group and IT, ME, and TE in the SVaD group. The svMCI group showed higher prevalence rates for ME (50%) and TE (50%) than the other measures (17% to 25%). On the other hand, the SVaD group showed higher prevalence rates in IT (62%), ME (54%), and TE (54%) than the other measures (31%). These results indicate that svMCI patients are more prone to have motor persistence, while SVaD patients are more prone to have motor akinesia and motor impersistence. Thus, motor impersistence can be considered an early symptom of MIDs, while motor akinesia represents a late symptom observed in more severe patients. Although this finding agrees with [PERSON] et al. (2011), more case studies are needed to generalize the results. The present study demonstrated the usefulness of the force tracking system in detecting patients with dysfunction in the action-intention system. Among patients with svMCI and SVaD, about 10% to 60% had dysfunction in the associated force control measure, implying that the force tracking system can be used to select brain-damaged patients who need clinical interventions to improve their symptoms.