## 4 Discussion  
In the present study, we divided patients with hemiplegic paralysis caused by strokes into three groups by motor paralysis level to study differences in the effectiveness of robot training according to with and without complete sensory loss. While little impact of the complete sensory loss was observed in the mild paralysis group, in the moderate and severe paralysis groups, accuracy of the reach motion and robot-training effectiveness may be reduced in patients with complete sensory loss. The present study is positioned as a preliminary case series study for a robot-aided rehabilitation aiming to improve the paralyzed arm function of stroke patients. In the current clinical practice, there is less applicability criterion of robot rehabilitation. For the reaching movement, vision and proprioception differently contribute to the planning of the motion [22]. [PERSON] et al. (2009) revealed that visual information mainly contributes to defining the kinematic plan and proprioception is for the transforming kinematic profile into the neural commands [22]. [PERSON] et al. (2019) suggest the importance of baseline somatosensory integrity for improving hand function after stroke [23]. Further, the combination of light touch and proprioception impairment has been revealed to relate with the upper limb motor recovery after stroke [14]. For the patients with a sensory disorder, therefore, the effectiveness of new technology on the neurorehabilitation should be discussed carefully. Especially in patients with complete loss of touch and position senses, there is no feedback other than vision in reach motion, thus a significant decrease in effectiveness could be predicted. In the present study, therefore, the effectiveness of robot rehabilitation for patients with complete sensory loss was compared with that of patients with similar paralysis and without complete sensory loss. In addition, it is difficult to investigate the role of proprioception in a study of healthy subjects because the proprioception cannot be completely masked experimentally. Thus, the present pilot study may be important to disseminate robot rehabilitation though there are few subjects. In the moderate and severe motor paralysis groups, the benefits of robot training for the FMA-total tended to be small for patients with complete sensory loss. Sensory disorder has been shown to reduce the degree of improvement of motor paralysis [14], and the improvement of paralysis through upper limb robot training in one case was small [16]. Our results are similar to those of previous studies and suggest that somatic sensory feedback contributes greatly to the improvement of motor paralysis through upper limb robot training. As shown in the patient with moderate motor paralysis and complete sensory loss, the FMA-total score was decreased by robot training. [PERSON] et al. (1990) reported that sensory disorder causes dyssynergia, resulting in patients becoming prone to dropping objects, bradykinesia, and clumsiness [24]. In this patient, the performance of grasping and/or manipulation did not improve sufficiently, and as a result, the FMA-total score including the functions of wrist and fingers might not improve. According to a report by [PERSON] et al. (2014), robot training of recovering stroke patients resulted in improvement of motor paralysis in 3 weeks (15 sessions) [18]. However, our results demonstrate a similar degree of paralysis improvement in only 2 weeks (10 sessions). The appropriate number and length of training sessions for robot training is unknown, and future studies must examine whether continued robot training achieves further improvements or whether the effects reach a plateau after 2 weeks. The RE and PE values are worse in cases with complete sensory loss than in cases without complete sensory loss for moderate to severe motor paralysis levels. These results suggest that the reach motion skill level and effectiveness of robot training are impacted by the degree of somatic sensory feedback.