## 3 Results
Despite the specificity of the stimulus application, no significant differences were found in SoE between the different conditions. A very interesting case study using an SCI patient combined somatosensory feedback in the form of muscular electrostimulation with visual feedback through the visualization of a virtual hand [37]. Here, the authors explored the different combinations between the congruence and incongruence of the different stimuli with MI action during BMI. The authors reported that somatosensory congruency was more effective in driving SoA. Ratings were higher when both feedback signals were congruent as compared to both being incongruent. When visual feedback was incongruent but somatosensory feedback was congruent, higher levels of SoA were reported as compared to the condition where visual feedback was congruent but somatosensory was not. The present review also aimed to explore the relationship between SoE variables and BMI performance. Of the 20 studies, 6 of them attempted to establish a relationship between reported SoE values and task performance in BMI. A positive relationship was found between SoO and BMI performance [13; 45; 52; 58]. Also, the SoA showed a significant correlation with BMI performance [13; 19]. Regarding SoL, two studies found a positive relationship with BMI performance [13; 58] while another one found no significant correlation [55]. The studies analyzed here focused mainly on the effects of congruence, synchrony, and likeness of stimuli and scenarios in SoE. A comparison between the number of sensory modalities, embodiment, and BMI performance does not support the existence of a clear relation between levels of embodiment, or its components, and BMI performance (refer to Table 4). Out of 17 studies where a comparison between BMI performance and SoE (or one of its components) values was possible, 11/17 = 64.7% involved a single modality. Moreover, 11/11 = 100% studies used had visual or visual immersive as the feedback sensorial modality. All of these eleven studies were associated with an increase in SoE or one of its components, but from the nine studies that reported both the values of embodiment and of BMI performance [13; 17; 19; 45; 51; 52; 53; 54; 58], five (5/9 = 55.56%) were associated with an increase in performance [17; 45; 53; 54; 58] and three (3/9 = 33.33%) [13; 19; 52] had no effect on performance. Only in one study (1/9 = 11.11%) [51], a detrimental effect in BMI performance occurred. Therefore, studies using a single feedback sensorial modality were all based on visual feedback, all reported increases in embodiment or one of its components, and approximately half reported improvements in BMI performance. A total of eight studies included two sensorial modalities (8/20 = 40.00%) [14; 18; 20; 36; 37; 55; 56; 57]. From these, 5/20 = 25.00% included visual (or visual immersive) and auditory feedback [14; 18; 20; 36; 55] and 3/20 = 15.00% included haptic feedback [37; 56; 57]. In two studies where visual feedback was paired with auditory feedback, an improvement in BMI performance and in SoE (or one of its components) occurred [14; 18]. In the remaining three studies, either no difference in BMI [20; 55] or in SoE [36] was reported. Meanwhile, in the three studies where haptic feedback was paired with visual feedback, no improvement in SoE nor in BMI performance was reported in one case [56], and no values were reported in another [57]. The third study with two haptic modalities [37] tested somatosensory and visual feedback and revealed that the congruent somatosensory feedback prevailed over incongruent visual feedback, namely increasing SoE and BMI performance. This study was performed in a single patient using intracortical recordings. Only one study included four different types of sensory feedback (visual, auditory, haptic vibratory, and haptic thermal) [15], but no difference in embodiment or in BMI performance was reported. It is noteworthy that this study was performed on a patient and included only 10 sessions.