Abstract
Progressive addition lenses (PALs) are used as spectacle lenses for presbyopia correction and are characterized by a progressive change of optical power leading to distortions in the periphery of the lens. These distortions change the perceived motion pattern during self-motion (optic flow) for the spectacle wearer, causing misperception of heading. Distortions vary spatially, with stronger distortions in the periphery and asymmetries between the upper and lower part of the lens, suggesting their influence on optic flow also varies throughout the visual field. PAL wearers themselves report unnatural motion perception during self-motion. To test possible inconsistencies in self-motion perception due to PAL distortions, we compared heading perception from distorted optic flow individually for each hemifield. Heading perception was tested in a VR-based simulation of lens distortions. Distortions were precomputed by ray tracing of real lens designs of two refractive corrections, and the image in VR distorted accordingly. In a psychophysical experiment, the self-motion of subjects moving across a ground plane was simulated with PAL distortions and an undistorted baseline condition. In this heading direction identification task, subjects estimated their perceived direction for different sampled translation angles. Perception for different hemifields was tested individually by performing the test with one hemifield masked out. A psychometric function was fitted to the subjects’ answers for each condition to determine the stimulus angle perceived as a straight forward movement (PSE). Results show a shift of PSE in the distorted conditions relative to the undistorted baseline condition. Heading estimation was significantly different between both hemifields, both in vertical and horizontal heading components, dependent on the type of lens. These results indicate that optic flow distorted by PALs is conflicting in its heading information. This inconsistent self-motion perception is a possible contribution to the distortion-related discomfort reported by many PAL wearers (“swim effect”).