Order Effects on the Rubber Hand Illusion Expectancy: A Replication and Extension of Lush (2020)

Abstract

The rubber hand illusion (RHI) is an illusion where the synchronized stroking of a rubber hand, placed in front of a participant, along with their concealed real hand results in a sense of ownership over the rubber hand. The questionnaire used to subjectively measure the RHI incorporated control and illusion statements to address demand characteristics. However, Lush (2020) demonstrated participants expected the illusion upon viewing a video of the RHI procedure despite the absence of tactile stimuli, indicating a lack of control over demand characteristics. In our study, Experiment 1, conducted with a Japanese sample (n = 27), was a preliminary direct replication of Lush (2020). Experiment 2, involving a larger sample (n = 185), also directly replicated Lush’s study and further investigated the influence of condition order on expectancies for the RHI. In both experiments, participants showed stronger agreement with the illusion statement expectancies in the synchronous condition compared to the asynchronous condition. However, this difference was not observed in the control statement expectancies, thereby replicating the outcomes of the original study. In Experiment 2, the group exposed to the asynchronous condition first showed stronger agreement with the illusion statement expectancies in that condition than those exposed to the synchronous condition first. As the RHI has been defined as the difference in direct and indirect measures between synchronous and asynchronous conditions, our results suggest that the methods in the RHI paradigm insufficiently control demand characteristics and order effects; thus, findings based on these methods are confounded by these effects.