Predictability, efference copies, and non-retinotopic motion

Perception is usually non-retinotopic. For example, visual perception is stable even though the retinal image is constantly changing due to eye and body movements. Likewise, a reflector on the wheel of a bicycle is perceived to rotate on a circular orbit, while its “true” motion (in retinotopic or exogenous coordinates) is cycloidal. In the first example, the brain uses efference copies to predict and compensate for eye movements. But how does the brain compensate for motion without efference copies? To investigate non-retinotopic motion perception, we used the Ternus-Pikler display. Two disks are flashed on a computer screen. A dot moves linearly up-down in the left disk and left-right in the right disk (retinotopic percept). If a third disk is added alternatingly to the left and right, the three disks form a group moving back and forth horizontally. The dot in the central disk now appears to move on a circular orbit (non-retinotopic percept), because the brain subtracts the horizontal group motion from the combination of the up-down and left-right motion. Here, we asked whether predictability is necessary to compute non-retinotopic motion. In experiment 1, the three disks moved randomly in any direction, rather than horizontally back and forth. Still, a strong non-retinotopic dot rotation was perceived. In experiment 2, we additionally varied the shape and contrast polarity of the stimuli from frame to frame. Still, a strong non-retinotopic dot rotation was perceived. Hence, the visual system can flexibly solve the non-retinotopic motion correspondence problem, even when the retinotopic reference motion is unpredictable. It seems that, in the case of non-retinotopic motion, the brain computes the reference-frame in real-time and does not need efference copy-like signals based on the predictability of the stimulus.

A New Approach to Non-Retinotopic Processing

Marco Boi

At every moment, the image the world projects on our eyes undergoes rapid and dramatic changes due to the eye movements and to the motion of the objects. Surprisingly, we are not aware of these changes, experiencing the world as stable and constant. This apparent contradiction suggests that our visual system uses non-retinotopic representations of the objects in the visual scene to create a stable percept of the world. Which visual mechanisms make use of non-retinotopic representations is a question of fundamental importance in neuroscience. The study of visual stability and non-retinotopic processing has classically focused on the problem of eye movements and has been studied in this context. We have proposed a new view on the problem of non-retinotopic processing that allows explaining how a stable percept of the world is created both across the movements of the eyes and objects. Based on this view, we devised an experimental paradigm that allows testing whether a given mechanism makes use of non-retinotopic representations and we applied it to several different visual processes. Our results suggest that non-retinotopic representations are used in higher-level visual processes whereas low-level mechanisms seem to operate on retinotopic representations.

EPFL2010

Binocular suppression occurs in object-centered coordinates

Marco Boi, Michael Herzog, Marcus Leonardus Vergeer

In binocular rivalry, only one image is perceived consciously when different, incompatible images are presented to the left and right eye, respectively. The other image is suppressed. Binocular suppression is generally assumed to occur within retinotopic coordinates. However, the world is continuously shifting on our retina because of the movements of the eyes and the objects themselves. Therefore, the visual system needs a mechanism to create binocular perceptual stability despite continuous changes in the retinal images. To investigate retinotopic versus object-centered binocular suppression, we combined the Ternus-Pikler paradigm with a binocular selective suppression paradigm. We presented a Ternus-Pikler display (TPD) in which three disks shifted by one position from frame 1 to frame 2. We presented a low-contrast grating in the central disk of the TPD to one eye and a high contrast bull’s eye at the same location to the other eye. The bull’s eye fully suppressed the percept of the grating. In the second frame, in half of the trials, a grating was presented on the central disk. In the other half, no grating was presented. The orientation of the grating (when presented) was the same as or orthogonal to the orientation of the first grating. No bull’s eye was presented in the second frame. Sensitivity to gratings with the previously suppressed orientation was reduced compared to orthogonal gratings, even though the gratings in both frames were presented at different retinotopic locations. These results are evidence for feature suppression in non-retinotopic, object-centered coordinates, giving rise to a new view on binocular rivalry where stimulus-selective, non-retinotopic inhibition is crucial in maintaining perceptual stability.

Association for Research in Vision and Ophthalmology2012

Non-retinotopic motion: Efference copies and predictability

Michael Herzog, Marc Michael Lauffs

Perception is usually non-retinotopic. For example, a reflector on the wheel of a bicycle is perceived to rotate on a circular orbit, while its retinotopic motion is cycloidal. To investigate non-retinotopic motion perception, we used the Ternus-Pikler display. Two disks are repeatedly flashed on a computer screen. A dot moves linearly up-down in the left disk and left-right in the right disk (retinotopic percept). If a third disk is added alternatingly to the left and right, the three disks form a group moving predictably back and forth horizontally. The dot in the central disk now appears to move on a circular orbit (non-retinotopic percept), because the brain subtracts the horizontal group motion from the up-down and left-right motion. Here, we show that predictability is not necessary to compute non-retinotopic motion. In experiment 1, the three disks moved randomly in any direction. In experiment 2, we additionally varied the shape and contrast polarity of the stimuli from frame to frame. In both cases, strong non-retinotopic rotation was perceived. Hence, the visual system can flexibly solve the non-retinotopic motion correspondence problem, even when the retinotopic reference motion is unpredictable and no efference copy-like signals can be used.

Sage Publications Ltd2015