Limb apparent motion perception: Modification by tDCS, and clinically or experimentally altered bodily states. (12th November 2021)

• Record Type: Journal Article
• Authors: Saetta, Gianluca; Ho, Jasmine T.; Bekrater-Bodmann, Robin; Brugger, Peter; Dijkerman, Chris H.; Lenggenhager, Bigna
• Is Part Of: Neuropsychologia. Volume 162(2021)
• Publication Date: 2021-11-12
• Subjects: Embodied cognition -- Apparent motion perception -- tDCS -- Lower limb amputation -- Body integrity dysphoria; Neuropsychology -- Periodicals; Neurology -- Periodicals; Psychophysiology -- Periodicals; Neuropsychologie -- Périodiques; Neuropsychology; Periodicals; Electronic journals; 616.8
• DOI: 10.1016/j.neuropsychologia.2021.108032
• Languages: English
• ISSNs: 0028-3932

Abstract

Abstract: Limb apparent motion perception (LAMP) refers to the illusory visual perception of a moving limb upon observing two rapidly alternating photographs depicting the same limb in two different postures. Fast stimulus onset asynchronies (SOAs) induce the more visually guided perception of physically impossible movements. Slow SOAs induce the perception of physically possible movements. According to the motor theory of LAMP, the latter perception depends upon the observer's sensorimotor representations. Here, we tested this theory in two independent studies by performing a central (study 1) and peripheral (study 2) manipulation of the body's sensorimotor states during two LAMP tasks. In the first sham-controlled transcranial direct current stimulation between-subject designed study, we observed that the dampening of left sensorimotor cortex activity through cathodal stimulation biased LAMP towards the more visually guided perception of physically impossible movements for stimulus pairs at slow SOAs. In the second, online within-subject designed study, we tested three participant groups twice: (1) individuals with an acquired lower limb amputation, either while wearing or not wearing their prosthesis (2) individuals with body integrity dysphoria (i.e., with a desire for amputation of a healthy leg) while sitting in a regular position or binding up the undesired leg (to simulate the desired amputation); (3) able-bodied individuals while sitting in a normal position or sitting on one of their legs. We found that the momentary sensorimotor state crucially impacted LAMP in individuals with an amputation and able-bodied participants, but not in BID individuals. Taken together, the results of these two studies substantiate the motor theory of LAMP. Highlights: Sensorimotor influence on visual limb apparent motion perception was examined. Dampening activity of the sensorimotor cortex reduced sensorimotor influence. Limb amputation and short-term leg immobilization reduced sensorimotor influence. Limb apparent motion perception relies on the observer's sensorimotor states.