Abstract
The levitation illusion is an example of a visual reorientation illusion (VRI) in which observers continue to feel upright while slowly tilted onto their backs in a room that tilts with them, remaining aligned with their body axis (Howard & Hu 2001, Perception 30: 583). Objects such as a ball hanging in the room appear to levitate. Similar VRIs are very significant in unusual environments such as microgravity.
We assessed the effectiveness of different fields of view (FOV) on creating the levitation illusion in York University's Tumbling Room. We varied FOV from unrestricted to approximately 15°x15° in a counterbalanced design. The content of the visual scene was controlled by viewing at twice the distance with half the FOV. Free viewing was compared to head fixed. Responses were categorized as ‘full’, ‘confused’ or ‘no effect’.
The majority of supine observers experienced the levitation illusion with unrestricted viewing. The effectiveness reduced systematically with reduction of FOV. Doubling the viewing distance revealed that this was not an effect of FOV per se but rather of the visibility of polarized visual features. A field of e.g. 30°x60° was equally effective at inducing a VRI as a 15°x30° field viewed from twice the distance. The incidence of VRIs was enhanced when subjects were allowed to move the head indicating that the features do not have to be visible all at once.
We conclude that VRIs, such as the levitation illusion depend critically on what can be seen but are not critically affected by the FOV.
Supported by NASA Cooperative Agreement NCC9-58 with the National Space Biomedical Research Institute, the Canadian Space Agency, and grants from the Natural Sciences and Engineering Research Council of Canada to L.R. Harris.