Seeing Size and Feeling Weight: The Size-Weight Illusion in Natural and Virtual Reality

Abstract

We experimentally tested the degree that the size-weight illusion depends on perceptual conditions allowing the observer to assume that both the visual and the kinesthetic stimuli of a weight seen and lifted emanate from the same object. We expected that the degree of the illusion depended on the "realism" provided by different kinds of virtual reality (VR) used when the weights are seen in virtual reality and at the same time lifted in natural reality. Welch and Warren (1980) reported that an intermodal influence can be expected only if perceptual information of different modalities is compellingly related to only one object. Objects of different sizes and weights were presented to 50 participants in natural reality or in four virtual realities: two immersive head-mounted display VRs (with or without head tracking) and two nonimmersive desktop VRs (with or without screening from input of the natural environment using a visor). The objects' heaviness was scaled using the magnitude estimation method. Data show that the degree of the illusion is largest in immersive and lowest in nonimmersive virtual realities. The higher the degree of the illusion is, the more compelling the situation is perceived and the more the observed data are in correspondence with the data predicted for the illusion in natural reality. This shows that the kind of mediating technology used strongly influences the presence experienced. The size-weight illusion's sensitivity to conditions that affect the sense of presence makes it a promising objective presence measure.