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Dynamic and Plasticity of Spatial Perception and Attention Neural Processes

Final Report Summary - DYNPSPANP (Dynamic and Plasticity of Spatial Perception and Attention Neural Processes)

The current project concerns human visual and spatial perception. Visual perception is the general ability to identify and give meaning to environment and objects around us while spatial perception allows us to organize visual stimuli in extra-personal space, to judge distances, sizes and localize our body and other objects in our surrounding environment.
Perception of our surrounding environment, which appears to be so absolute and fundamental, can in fact be modified. Visual perception of objects, their identity, their spatial position or their size, for example, can be indeed altered or modified by a peripheral or cortical damage, experimentally (in a laboratory) by several sensori-motor manipulations or even by our everyday experience (such as our reading and writing habits). For example, in healthy and brain-damaged adults, spatial judgments can be laterally biased: it is the case in right-brain damaged patients with left Unilateral Spatial Neglect (USN) who set the subjective middle of a line to the right of the true center, and in healthy adults who can show a reverse, albeit much smaller, bias, a phenomenon called ‘pseudoneglect’. Visual and spatial perception appears thus to be a dynamic process under the influence of different factors that need to be uncovered. Understanding how visual and spatial perception is built and how it can be modified is crucial as visual and spatial perception is involved in everyday life activities.

However, equally or even more important is our ability to act on the environment adequately and very quickly. And sometimes we might need to act before having a full conscious understanding of the outside world. We are sensori-motor individuals and most of time, we are acting while we are giving meaning to the environment, suggesting a close link between what we do and what we see, and adaptation to our environment requires this close link between action and perception.

According to the standard view of visual processing, the way we judge and give meaning to surrounding objects and the way we act on them rely on different independent cognitive systems. According this view, visual and spatial perception is considered as a purely perceptive function. It is thus traditionally studied in passive conditions, where we have to judge and give meaning to visually presented objects without moving or acting on these objects. In this project, we attempt to reach a more generalized understanding of visual and spatial perception: We want to show that our perception of the world depends on our previous and present experience, and more particularly on whether and how we act and we have acted on the world.

We thus developed a series of studies in order to examine the influence of on-going and previous action on visual and spatial perception. Some studies have focused on behavioral effects of on-going and previous action on perception while others studies have focused on neuro-functional effects. The former aimed at examining how action modulate perception in humans while the later, still in progress, aims at exploring the cerebral correlates of these effects.

In a first series of experiments, we showed that our perception of an object actually depends on whether we are acting or not on this object. In these experiments, we compared visual perception performances in two conditions: when visual judgements were performed alone (i.e. passively as in most classical experiments), with a condition where visual judgements were performed concurrently with a motor task. To assess visual judgements, we used a procedure, called Object Substitution Masking (OSM), that allowed us to mask the visibility of the target and to examine how and when in the visual processing hierarchy, the motor system exerts its influence on visual processing. OSM consists to briefly present a visual array, composed of a target among other similar objects, and to mask the visibility of the target by the trailing presentation of four-dots around the target (the four dots acting as a mask of the target). Our data showed that preparing a pointing action on the target not only improve its identification but also modulate the masking effect. It strongly suggests that on-going action can improve perception by affecting very early visual processes. Experiments currently in progress are testing whether visual processing devoted to action are altered by OSM as it is the case for visual processing devoted to object identification. Positive results would further support the close link between action and perception.

In a second series of experiment, we showed that spatial perception actually depends on how we have acted on our environment. Spatial judgments were examined before (pre-test), and after (post-test) a second training motor task (test) intended to ‘modulate’ spatial perception. We examined the influence of the motor task (test) on spatial judgements by comparing pre- and post-tests performances. Different components of the motor task were manipulated: (1) its geometry by using a lateralized pointing task (LPT) in which participants were asked to point to leftward target, or rightward targets compared to a control condition in which targets were centered, (2) its coherence by using virtual reality devices in which random force-field perturbations strongly prevent participants to correctly execute the task. This later project is based on a multi-disciplinary approach, combining the strong potential of cognitive and experimental psychology, neurosciences, as well as virtual reality. At this point, we showed that visuo-spatial judgments depend on previous sensori-motor coherence. Our results revealed that the mere perturbation of the motor system for 5-minutes is sufficient to induce transient lateral shift of spatial perception. These results further argue in favor of a close action-perception relationship and strongly suggests that altering the motor system is able to induce spatial perception plasticity. Experiments combining similar protocols with EEG signal recording are currently in progress in order to study the neural substrate and time course of spatial perception plasticity induced by previous action properties.

These data are promising on a theoretical point of view as they challenged current classical model, in which visual processing devoted to object identification and visual processing allowing us to perform an action on objects are claimed to be independent. This work showed instead that the way we act and we have acted on the world shape our perception of objects, their identity and their spatial properties. This implies that visual judgements assessed in passive conditions, as in most experiments dealing with visual perception, do not likely reflect visual performances outside the laboratory, where individuals are usually interacting with objects they are perceiving. Future studies should at least, test the generalization of their conclusion to more ecological conditions in which visual performances are assessed with a concurrent motor task.
This work may have some implications on educational domain. These data bring empirical data supporting any programs that promote interactions with and within the environment. Our data bring evidence in favor of the idea that acting on objects improves our perception of these objects.
Finally, this project promises also important progress for clinical researches in the understanding of causes and rehabilitation of space disorders by providing behavioral and neuro-functional experimental data in favor of the disconnection hypothesis of unilateral spatial neglect.