## 4 Discussion
However, it is still inconclusive whether congruence of vibratory feedback [18] or auditory feedback stimuli [56] leads to a higher level of SoE. Only one study included in this review, which focused on an SCI patient, found that the congruence of the haptic feedback might have a greater influence on the induction of SoA than the congruence of the visual feedback [37]. However, it should be noted that the haptic stimulus used in that study involved muscular electrostimulation, which induces movement through muscular contraction and can be considered haptic-kinesthetic feedback. This type of feedback cannot be directly compared to haptic-tactile feedback, such as that resulting from vibration, as they have very different characteristics. Interestingly, despite the importance of congruence in the feedback stimuli, the presence of visual feedback, even if incongruent, appears to have a more positive effect on SoE than its absence [52]. In addition to the feedback related to the action or the virtual/robotic actor, studies have also focused on the realism of the virtual scenario where that action took place. For example, the study by [PERSON] and colleagues [15] incorporated auditory and thermal stimuli that were coherent with a highly realistic virtual reality environment. Similarly, in the study by [PERSON] and colleagues (et al., 2011), the visual elements necessary for the operation of an SSVEP-BMI were contextualized [51]. The results of the present review support the notion that visual sensorial feedback is beneficial for the SoE and that multisensory feedback combining visual and auditory or visual and haptic feedback tends to be beneficial for SoE, though not necessarily for BMI performance. As elegantly demonstrated in the single-SCI-patient study by [PERSON] and colleagues [37], it is likely that the interplay of different sensorial modalities may be critical at specific points in time. Lastly, while the present review does not support the hypothesis that multisensory feedback necessarily improves SoE and BMI performance, the study of [PERSON] and colleagues [15], performed in a single SCI patient, suggests that including visual (immersive), auditory, vibratory, and thermal feedback is not detrimental to embodiment and BMI performance. However, any extrapolation of findings from these latter studies needs to be approached with caution due to the small number of patients and the fact that SCI patients already have an altered SoE. After analyzing the studies associated with SoE and multisensory feedback during BMI control, it is proposed here that a detailed examination of the effects of each type, as well as the combination, of sensory modalities is crucial for our understanding of the neural basis of SoE (and SoO, SoA, and SoL) and how it relates to BMI performance. To achieve this, it is critical to systematically evaluate the effects of removing and adding each sensory modality, or combinations of modalities, in various types of tasks (SSVEPs, MI, P300) and with different types of neural signals (EEG, functional magnetic resonance (fMRI), intracortical recordings, etc.). We suggest that a series of experiments using within-subject designs could help control for individual differences in physiological parameters. Additionally, this review highlights that only a limited number of studies have been conducted in SCI patients [15; 18; 37; 56]. These studies, although conducted in a small number of patients (\(N=1\)-\(8\)), allowed for the examination of SoE in pathological conditions and provided significant insights that could not otherwise be studied. Therefore, it is relevant for future studies to specifically address the role of multisensory feedback in SoE during BMI control in SCI and other patients. It is noteworthy that a large fraction of the BMIs analyzed here required users to engage in active motor imagery, with instructions to avoid making actual movements. However, in the context of rehabilitation, motor imagery BMIs are typically employed to promote or facilitate specific motor activities [15; 37].