Multimodal integration in the estimation of walked distances

When walking through space, both, dynamic visual information (i.e. optic flow), and body-based information (i.e., proprioceptive/efference copy and vestibular) jointly specify the magnitude of a distance travelled. While recent evidence has demonstrated the extent to which each of these cues can be used independently, relatively little is known about how they are integrated when simultaneously present. In this series of experiments, participants first travelled along a predefined distance and subsequently matched this distance by adjusting an egocentric, in-depth target. Visual information was presented via a head-mounted display and consisted of a long, richly textured, virtual hallway. Body-based cues were provided either by walking in a fully-tracked, free-walking space or by walking on a large, linear treadmill. Travelled distances were provided either through optic flow alone, body-based cues alone (i.e. blindfolded walking), or through both cues combined. In the combined condition, visually-specified distances were either congruent (1.0x) or incongruent (0.7x or 1.4x) with distances specified by body-based cues. The incongruencies were introduced either by changing the visual gain during natural walking or the proprioceptive gain during treadmill walking. Responses reflect a combined effect of both visual and body-based information, with an overall higher influence of body-based cues