## 3 Results
(2009), a proprioceptive drift was objectively measured by asking the participants to indicate, without looking, the location where they perceived the real hand to be placed after a virtual arm-moving task in the BMI [16]. Meanwhile, in the study of [PERSON] and colleagues [20], participants were questioned about the movement of the virtual hands over their own hands. Apart from these subjective measures for SoE, three additional studies from the same group also assessed the SCR following a threatening stimulus to a non-real body part (injection in the robot hand) [12; 52; 54]. This procedure intended to assess more objectively how embodied the participant with the external body parts was during the BMI task. For this, the authors measured the physiologic changes (trough the assessment of SCR) in the real body during the BMI-performing task. Across the three studies, the SCR was higher in the experimental conditions with higher scores of reported SoO. In addition, this was also verified for SoA when it was included as a variable [54]. In another study, electromyography (EMG) was used to estimate the amount of muscle activity required to perform a virtual task if it occurred in the real world [16]. The group with higher EMG activity also reported higher levels of SoO. Providing sensory feedback while performing BMI tasks is one of the presumed strategies used to improve BMI performance itself [62; 63]. It is hypothesized that this agreement between stimuli and actions is relevant to the SoE experience. However, few studies explore the contribution of different sensory modalities to SoE. All studies included in this review used visual stimuli as their main sensory modality (see Figure 3). Although the auditory modality was present in six studies, and some form of haptic stimulus was present in four studies, none of them specifically quantified the influence of these stimuli on the SoE variables. Immersive visual feedback was present in 14 studies whereas the others used non-immersive visual feedback. Normally the non-immersive visual feedback was received through a computer screen. Only in one study, the visual feedback was non-virtual with participants observing a robotic hand moving in front of them [36]. Within the visual feedback modality, the immersive type has shown higher levels of SoE compared to the non-immersive type [13]. The congruence or incongruence of the visual stimulus with the MI action performed seems to have a strong impact on SoE. Congruent visual stimuli seem to increase SoO [12; 16; 52]. However, differences between studies were found for SoA. In one study, no significant differences were present in SoA levels between incongruent and congruent visual stimulus conditions [16]. In contrast, another study reported a negative impact of visual incongruence on SoA [19]. These differences may find some explanation regarding the type of visual stimulus that was provided. Although both used a non-immersive form of visual feedback, in the study by [PERSON] et al. (2009), the feedback was based on the movement of a virtual hand, while in [PERSON] et al. (2015), the feedback congruence was associated with the displacement of a virtual bar on a screen. In this second study, it was also verified that larger delays negatively impact the SoA. However, for delays under 1000 ms, no significant differences were found [19]. This information becomes relevant to understand the acceptable limit of delay in this type of BMI technology, since any feedback addition has some amount of expected delay due to the normal computational processing. In the only study where the congruency of an auditory stimulus with a visual stimulus was explored, no significative impact on the SoE was found [18]. The realism of sensorial feedback seems to enhance more realistic responses of the participants that are exposed to it [15; 44; 64].