## 5 Discussion  
This paper showed that the accuracy of angle prediction can be affected by some psychological factors. The basis for this is that the elbow joint angle can be estimated by the sEMG signal during continuous motion using a classification or regression algorithm. For the elbow joint motion control based on the sEMG signal, at present, the classification recognition error using the motion type or the motion direction is relatively high. However, the features of the sEMG signal are converted to joint angle values through the regression method and then directly applied to the exoskeleton actuator, which is more able to ensure continuous matching of human-machine motion. This also effectively compensates for the inflexibility of classification recognition. Although there is still a large error in angular regression, we have found that these errors can be appropriately reduced under some psychological conditions. The results of this paper can be used as a basis for more optimal sEMG control. Many people intuitively believe that visual feedback is necessary to produce a constant level of force and believe that providing more frequent visual feedback can contribute to a reduction in motion variation. However, many results also show that the maintenance of exercise stability can be promoted by proprioceptive information [26]. As in our experiments, subjects in the blink of an eye can better move the elbow joint from 0\({}^{\circ}\) to 90\({}^{\circ}\) based on visual cues. It is also possible to achieve this requirement by relying on proprioception when closing the eyes. From the experimental results, the accuracy of elbow joint angle recognition under proprioceptive conditions is higher than that of visual feedback. The wider force fluctuations in the presence of a continuous visual feedback were explained by continuous sensorial information, which possibly induced the subject to a greater number of adjustments and corrections of the force output [27]. This also leads to a reduction in the degree of automatic movement. [PERSON] et al. [28] showed that the amplitude of force fluctuation, an index of force stability, is also inversely related to the level of effort and to the number of the recruited motor units. The results of [PERSON] et al. [29] also show that the complexity of the force variability (signal noise) is lower without visual feedback. More importantly, there are instances where the visual and proprioceptive senses \"overlap\", informing the brain about common conditions of the body and its environment [30]. However, discrepancies may also arise due to the inherent differences in the filtering characteristics of the two kinds of sensing information and the difference in the coordinate reference will cause the information provided to the brain to be inconsistent, so that the mapped joint angle produces more complex nonlinear calculations [31]. The visual and proprioceptive sensory organs encode position information in different coordinate frames, so there will always be \"disagreement\" between visual and proprioceptive feedback of limb position and movement. Proprioceptors inherently encode muscle length and rate of length change, while vision encodes object location in egocentric coordinates. Although in many cases, the sEMG control requires visual feedback to help maintain the accuracy of the output target as much as possible. However, the main concern in our research is not the accuracy of the motion but the accuracy of the angle recognition. This is a study of the stability of  
Figure 6: Coherence of EEG (C3 electrode) and sEMG in vertical motion. motion and the adjustment of compensation actions, reflecting the functional coordination mode of the relevant muscles. [PERSON] et al. [29] concluded that different types of visual feedback are inversely related to the stability of muscle force. The proprioception mainly enhances the more natural dynamic transformation between motions.