Tilting the balance: do balance abilities predict the body tilt illusion?

Previous research reveals that participants show a consistent bias in overestimating the angle at which their body is tilted. This is called the body tilt illusion. The illusion strengthens with limited sensory information, particularly when visual information is removed, which highlights the potential protective purpose of the illusion. In this sense, a stronger illusion may help one to maintain their balance when valuable sensory information is inaccessible. Although research has examined the contributing factors of audition and vision to the body tilt illusion, the potential role of vestibular information has yet to be studied. Hence, the current study seeks to examine how balance abilities, tilting direction, and visual information may each contribute to the body tilt illusion. Twenty-nine participants completed a series of balancing tasks followed by eight body tilting trials on a human-sized 3D gyroscope and finished with a brief demographics and exercise questionnaire. As expected and consistent with past research, participants experienced a stronger body tilt illusion with their eyes closed compared to eyes open. Additionally, participants exhibited a stronger body tilt illusion when tilted sideways along the coronal plane compared to forward and backward along the sagittal plane. Participants also experienced a stronger body tilt illusion when tilted backward compared to forward. Lastly, stepwise multiple regression analyses suggest that balance is unrelated to the body tilt illusion. Hence, while balance abilities appear to be unrelated to the body tilt illusion, the results support the notion that the body tilt illusion serves a protective purpose when tilting (or falling) in a higher-risk situation. Just as falling with eyes closed is riskier than falling with eyes open, human anatomy suggests that falling sideways along the coronal plane is riskier than falling forward/backward along the sagittal plane and falling backward is riskier than falling forward.