Abstract
Some optical elements, like corrective spectacle lenses with a progressive change in optical power, distort the visual field of the wearer. Optical distortions alter visual form and motion features, processed also up to higher areas of the visual system. Consequently, as has been shown, adaptation to distorted natural stimuli induces spatiotopic aftereffects: after a saccade subsequent to adaptation, aftereffects are present not only at the adapted retinal location, but also at the spatial location of adaptation stimulus. Because of the spatial variation of distortions in lenses, eye movements constantly modulate strength and orientation of the distortions present in the visual field. For progressive addition lenses, for example, left and right part of the lens skew distort the visual field in opposite directions. Switching gaze from one side to the other could stimulate adaptation with opposing retinotopic and spatiotopic aftereffects. For this study, 10 subjects were presented with two oppositely distorted adaptation stimuli simultaneously. To do so, a video with natural image content was skew distorted in opposite directions. Both distorted videos were shown simultaneously at distinct locations on the left and right side of a screen. Gaze was controlled by eye tracking and guided to repeatedly switch between the two stimuli during the 5 minutes of adaptation. Aftereffects of distortion adaptation were measured in a motion direction identification task. Before and after adaptation, the motion angle of a group of coherently moving dots perceived as horizontal was determined for both stimulus locations independently. A significant difference was found in the shift of perceived motion direction between the two stimulus locations. The direction agrees with the distortion direction shown during adaptation at the respective screen locations. Therefore, in case of prolonged adaptation with gaze switching between opposite skew distortions, retinotopic aftereffects of distortion adaptation are suppressed by the spatiotopic adaptation effects.