Spatial configuration in rubberhand illusion research : A meta-analysis

Abstract: In the rubber hand illusion (RHI), a rubber hand is placed in front of the participant with the participant's hand out of sight. If both hands are touched simultaneously, the illusion typically occurs. Between RHI studies, differences can be seen in the setup, and results of the illusion strength are inconsistent. One of these differences can be the moving RHI, where the real and rubber hand make the same movements to induce the illusion. The differences led to uncertainty regarding the influence of spatial configuration (i.e., an arrangement of the setup within three-dimensional space) on the illusion of body ownership. With this meta-analysis, I quantify the illusion strength in the moving RHI to be able to conclude if spatial configuration influences the results. A total of nine studies were included that had a total of 391 participants. The results show that the synchronous condition has a stronger illusory effect than the asynchronous condition. However, due to heterogeneity, the sample size may not represent the general population. Sub-group analysis showed no major difference in the illusion strength between a vertical and horizontal setup. These observations do not correspond with classical RHI studies in which vertical and horizontal setups were compared. However, in this meta-analysis, only moving RHI studies were included. In the moving RHI, the experimenter does not enter the visual receptive field of the participant, which may explain why no differences between the setups were found. The results of this meta-analysis cannot be seen as definitive; more research is necessary.