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PLAsticiTY of Perceptual space Under Sensorimotor interactions

Periodic Reporting for period 1 - PLATYPUS (PLAsticiTY of Perceptual space Under Sensorimotor interactions)

Reporting period: 2017-07-01 to 2019-06-30

Space is a fundamental dimension of physical and perceptual reality. However, physical space and perceptual space are not the same. Although we experience space as a uniform physical entity around us, the properties of the sensory systems and of our behavior, as well as many visual illusions, clearly show that perceptual space is constructed by the brain and decoupled from its physical counterpart. Recent research has shown that visually perceived space is strongly influenced by eye movements and can thus be understood as part of an action-perception loop that is geared towards appropriate behavior to ensure survival. Past research has mostly considered static conditions, in which a given motor act is performed and its impact on spatial perception is studied. The brain, however, is a learning machine. Outcomes of behavior almost always are used to update internal processes to adapt the system better to its environment. PLATYPUS investigates how visual space is shaped and maintained via adaptive interactions with eye- and arm movements. Research within PLATYPUS will lead to novel insights on the nature of perceptual space and a more complete view of spatial perception. These insights have strong potential for translation into applied fields. On the one hand, adaptive changes to visual perception and motor behavior occur whenever one needs to adjust to the wearing of new glasses, especially when they contain progressive lenses. Since all people develop presbyopia with age, and in about a fourth of the population presbyopia is co-morbid with myopia, this affects a large part of the population in the EU and elsewhere. On the other hand, PLATYPUS insights could potentially enhance the effectiveness and efficiency of applications employing virtual reality, be it in the private (e.g. gaming community) or in the public sector (e.g. health-care industries).
In period 1 of the project all scientific work packages have started as planned. In WP 1, we have collected and analysed neural data in dorsal visual stream areas PE, V6A, and VIP to study the dynamics of eye and arm signals in reaching targets in the 3-dimensional space as well as human behavioral data on perceptual and motor consequences of an adaptation of eye position. In WP 2 we have performed a precise mapping of the blind spot in the living human eye and modelled position estimates upon read-out of a sensory or motor map of space that generates a continuous spatial representation across the region of the blind spot. Furthermore, we have measured the same paradigms in non-human primates to uncover the cortical mechanisms of spatial filling-in. In WP 3 we have established a setup for the study of eye blinks and the perception of spatial location changes, luminance changes, and temporal intervals across blinks in comparison to saccades in order to establish whether blinks and saccades share perceptual processing mechanisms. Furthermore, in WPs 3 and 4 we have developed a setup for the measurement of perceived size of spatially extended vertically oriented stimuli before and after saccadic adaptation. In WP 5 we have developed and tested techniques for simulating distortions such as those experienced when wearing progressive additional lens glasses in gaze-contingent virtual reality displays. Furthermore, we have evaluated experience dependent long-term facilitation of fast adaptation to image skew, a common distortion in progressive additional lens glasses.
How visual spatial maps in the brain serve perceptual and behavioral purposes is still under question. Platypus brings together viewpoints obtained from studying different animal species and behaviors with complementary experimental and theoretical techniques. We compare the functional specializations of the “vision-for-action”, dorsal stream networks in new world monkeys with those of old world monkeys and humans to better understand their specifics and commonalities. We will further clarify how these maps combine visual input with eye movement information to provide spatial representations that can be used to guide reaching movements and to distinguish external from self-generated visual motion. We will study plastic changes in this representation by using adaptation of eye position and determine its consequence on spatial behavior.

The blind spot, an area of the retina that cannot receive any visual input is used in Platypus as a tool to infer infer dynamical properties of the perceptual map. Being devoid of visual input, the blind spot provides one of the clearest and simplest examples of the difference between physical and perceptual space: we do not experience a gap in perception due to filled-in contextual information from around its border. Platypus will characterize the neuronal mechanisms of maintaining space in and around the blind spot and use the blind spot filling-in to investigate plastic processes in the maps and their relationship with spatial perception. The results and the developed paradigms will be applied to the study of scotomas (blind areas resulting from ocular diseases) using virtual reality simulations.

Since Platypus aims to understand how changing a motor representation is linked to changes in visual space we study whether spatial plasticity is driven directly by oculomotor adaptation or whether it is a consequence of the change of the visual scene occurring during an eye movement. We investigate whether similar plastic effects occur for eye blinks as for gaze shifts, two different types of interruption of the visual input. We search for the physiological basis of the adaptation-induced changes to spatial perception. We also study how changes in spatial or motor coordinates translate into changes in the perception of the size and shape of objects and in reaching movements towards objects.

The research on plastic aspects of visual and motor space in PLATYPUS is strongly related to applied issues in optometry and ophthalmology. The developed paradigms will be used for translational approaches, i.e. they will be applied to study perceptual and motor changes in conjunction with wearing progressive additional lens glasses. Progressive additional lenses introduce different geometric distortions in different parts of the visual field, producing a direct coupling between eye position and size perception. Platypus will study the implications of this coupling for applications in wearers of progressive additional lenses. Our approach involves virtual reality simulations of such optical distortions coupled with eye tracking in gaze contingent head-mounted displays in order to develop training tools.