Abstract
In the past, retinal flow (RF) was purported to contain sufficient information for determining our direction of motion during locomotion (Gibson, 1958). It has now been shown that other sources of information, both retinal and extra-retinal (ER), can contribute useful information for heading judgement (Banks et al, 1996; Wann J.P. & Wilkie R.M. ARVO 2001). In the case of active steering, accuracy can be maintained if RF is highly salient and is combined with ER information, whereas if RF is degraded other retinal cues such as a visual reference (VF) for egocentric direction are required (Wilkie R.M & Wann J.P. ARVO 2001). The visual system appears to combine different sources of information, with flexible weighting, to allow robust control even where some cues might be degraded. This experiment explored cue combination further by adding an erroneous directional bias to the RF by rotating the ground plane around the point of visual fixation (target) during steering. Veridical ER was supplied, a visual frame of reference (VF) was manipulated and errors in steering accuracy compared. Results showed that bias in the flow caused the participant to over- or under-steer even with appropriate ER and VF. This provides evidence that even when strong ER and VF information is present, which could provide a steering solution (Wann & Land, 2000), there is still a weighting attached to RF information.
Supported by the UK EPSRC.