Vol.:(0123456789) 1 3 Psychological Research https://doi.org/10.1007/s00426-020-01366-5 ORIGINAL ARTICLE Visual feedback from a virtual body modulates motor illusion induced by tendon vibration Gabriele Fusco 1,2  · Gaetano Tieri 2,3  · Salvatore Maria Aglioti 1,2 Received: 27 December 2019 / Accepted: 22 May 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract Frequency-specifc tendon vibration (TV) elicits illusory kinesthetic sensations around the vibrated body parts. Studies indi- cate that vision plays a fundamental role in modulating such illusions. In our current study, we used immersive virtual reality (IVR) to investigate the role of body-related visual feedback in modulating illusory sensation of movement in the left arm. Thirty healthy participants were asked to evaluate the onset of motor illusion and four illusion-related features (vividness, duration, extension and afterefect), in the presence and absence of real and virtual visual feedback. Additionally, subjective reports of the embodiment illusion (the sense of embodying a virtual surrogate) were collected in virtual conditions. Results showed a progressive decrease in the perception of the motor illusion along a continuum ranging from the absence of visual feedback (maximal illusory perception) to the observation of one’s own real arm (minimal illusory perception). Interestingly, the appearance of the virtual limbs afected the movement illusion diferently. Specifcally, TV evoked a stronger kinesthetic illusion when observing the virtual hand detached from the limb than during the observation of the virtual full limb and virtual object. This suggests that a closer visual resemblance between the virtual and real limb results in a greater efect on proprioceptive processing. However, no signifcant correlation was found between the illusion of arm movement and the illusion of embodiment, indicating that the two phenomena may not be directly related. These fndings provide new insight into the role of body-related visual feedback in modulating motor illusions. Introduction In everyday life, our interactions with the environment rely on our ability to control our body. This involves a complex combination of processes and requires the integration of motor control and sensory feedback. Proprioception, or sense of position, is mediated by receptors widely distributed within the joints, tendons, and muscles, and plays an impor- tant role in these processes (Sherrington, 1906). Propriocep- tion depends on the activation of muscle spindle primary endings, a group of receptors (Ia fbers) located within the muscular tissues that respond to changes in muscle length, tension, and rate of stretch (Granit, 1975; Proske, 2006). The perturbation of these organs generates proprioceptive feedback signals that run along the aferent pathways of the nervous system, updating the motor representations of the body state and facilitating postural stability and movements (Riemann & Lephart, 2002a, 2002b). Mechanical vibration applied to peripheral tendons (ten- don vibration, TV) alters the muscle spindle activity, induc- ing illusory kinesthetic sensations and misjudgments about the position of the afected body parts (Jones, 1988). The aferent signals triggered by TV are conducted to the fronto- parietal brain areas (Naito et al., 2002, 2007; Cignetti et al., 2014), eliciting an illusory sensation of arm movement, with the sensation of movement being in the same direction as if the stimulated joint were actually stretched (Goodwin et al., 1972; Naito & Ehrsson, 2001). Following termination of TV, the muscle spindles decrease their activity, restoring the resting state and generating a transient opposite illusory movement (i.e., the sensation that the limb has returned to its original position) or “afterefect” of the stimulated body part (Ribot-Ciscar et al., 1998; Seizova-Cajic et al., 2010). Gabriele Fusco and Gaetano Tieri contributed equally to this work. * Gabriele Fusco gabriele.fusco@uniroma1.it 1 Department of Psychology, Sapienza University of Rome and CLNS@SAPIENZA, Istituto Italiano Di Tecnologia, Rome, Italy 2 IRCCS Santa Lucia Foundation, Rome, Italy 3 Virtual Reality Lab, Unitelma Sapienza of Rome, Rome, Italy