Abstract
Monocular vision coupled with active movement of the head enables observers to recover quite accurate estimates of object distances in the near space (Panerai et al., 2001; Peh et al., 2001). We investigated the roles of optical vs. head movement related information in a monocular distance estimation task. Subjects viewed at eye level spherical objects textured with random dots and used fronto-parallel movements of the head to explore them. In normal conditions object tracking during self-motion produces coherent optical and extra-retinal (i.e. proprioceptive and vestibular) information. In two separate experiments, the coherence between visual and extra-retinal cues was altered. In the first experiment, the spherical object was rotated around its centre at an angular speed proportional to subject's linear head velocity. In this condition the oculomotor behaviour is preserved but the optic flow increases or decreases according to the gain. In the second experiment, the spherical object was rotated around the subject's momentary eye position at an angular speed proportional to the head's linear velocity. In such situation the optic flow is preserved but the eye movement required to maintain gaze on the target is increased or decreased according to the gain. Results from experiment 1 seem to indicate that a gain larger than the unit determines an underestimation of object distance. Although more data will be required, this preliminary finding tends to exclude the hypothesis that perceived distance might be derived by processing pure extra-retinal signals (i.e. oculomotor, vestibular). References
PaneraiFCornilleau-PérèsVDroulezJ.“Contribution of extra-retinal signals to the scaling of object distance during self-motion”, Perception & Psychophysics (submitted).
PehC. H.PaneraiF.DroulezJ.Cornilleau-PérèsVCheongL. F.Absolute distance perception during saggital head motion. Submitted to VSS, Saratosa, May 8-2001.