Enhancing implicit change detection through action

Implicit change detection demonstrates how the visual system can benefit from stored information that is not immediately available to conscious awareness. We investigated the role of motor action in this context. In the first two experiments, using a one-shot implicit change-detection paradigm, participants responded to unperceived changes either with an action (jabbing the screen at the guessed location of a change) or with words (verbal report), and sat either 60 cm or 300 cm (with a laser pointer) away from the display. Our observers guessed the locations of changes at a reachable distance better with an action than with a verbal judgment. At 300 cm, beyond reach, the motor advantage disappeared. In experiment 3, this advantage was also unavailable when participants sat at a reachable distance but responded with hand-held laser pointers near their bodies. We conclude that a motor system specialized for real-time visually guided behavior has access to additional visual information. Importantly, this system is not activated by merely executing an action (experiment 2) or presenting stimuli in one's near space (experiment 3). It is activated only when both conditions are fulfilled, which implies that it is the actual contact that matters to the visual system.     

Watch this! Observed tool use affects perceived distance

Recent research has shown that being able to interact with an object causes it to be perceived as being closer than objects that cannot be interacted with. In the present study, we examined whether that compression of perceived space would be experienced by people who simply observed such interactions by others with no intention of performing the action themselves. Participants judged the distance to targets after observing an actor reach to an otherwise unreachable target with a tool (Experiment 1) or illuminate a distant target with a laser pointer (Experiment 2). Observing either type of interaction caused a compression of perceived space, revealing that a person’s perception of space can be altered through mere observation. These results indicate that shared representations between an actor and observer are engaged at the perceptual level easily and perhaps automatically, even in the absence of cooperation or an observer’s own intention to interact.     

How tool use and arm position affect peripersonal space representation

Experiment 1 investigated whether tool use can expand the peripersonal space into the very far extrapersonal space. Healthy participants performed line bisection in peripersonal and extrapersonal space using wooden sticks up to a maximum of 240 cm. Participants misbisected to the left of the true midpoint, both for lines presented in peripersonal and for those presented in extrapersonal space, confirming a peripersonal space expansion up to a distance of 240 cm. Experiment 2 investigated whether arm position could influence the perception of peripersonal and extrapersonal space during tool use. Participants performed line bisection in the peripersonal and in the extrapersonal space (up to a maximum of 120 cm) using wooden sticks in two different conditions: either with the arm bent or with the arm stretched. Results showed stronger pseudoneglect in the stretched arm condition.     

Embodied perception of reachable space: how do we manage threatening objects?

This study aimed at determining whether the size of reachable space is affected by the level of danger of some everyday manipulable objects. Two possibilities are examined: Dangerous objects affect the size of reachable space because of long-term semantic knowledge of their potential hurtful value or the on-line relation between objects’ dangerous attributes and the body. The experimental paradigm combined the danger value (dangerous/not dangerous) and the orientation of objects (e.g. pointing away from/towards the perceiver). Reachability judgments measured the size of peripersonal space, and perception of objects’ danger was estimated through questionnaires. Results revealed that, whatever the estimated level of objects’ danger, the extent of peripersonal space was reduced when the threatening part of dangerous objects was oriented towards participants, not when oriented away. This suggests that the characteristics of the here and now body-objects interaction are crucial in affecting the boundary of peripersonal space.     

Embodied perception of reachable space: how do we manage threatening objects?

This study aimed at determining whether the size of reachable space is affected by the level of danger of some everyday manipulable objects. Two possibilities are examined: Dangerous objects affect the size of reachable space because of long-term semantic knowledge of their potential hurtful value or the on-line relation between objects' dangerous attributes and the body. The experimental paradigm combined the danger value (dangerous/not dangerous) and the orientation of objects (e.g. pointing away from/towards the perceiver). Reachability judgments measured the size of peripersonal space, and perception of objects' danger was estimated through questionnaires. Results revealed that, whatever the estimated level of objects' danger, the extent of peripersonal space was reduced when the threatening part of dangerous objects was oriented towards participants, not when oriented away. This suggests that the characteristics of the here and now body-objects interaction are crucial in affecting the boundary of peripersonal space.     

Social exclusion modulates pre-reflective interpersonal body representation

Perception of affordance is enhanced not only when that object is located in one’s own peripersonal space, as compared to when it is located within extrapersonal space, but also when the object is located in another person’s peripersonal space [as measured by a spatial alignment effect (SAE)]. It has been suggested that this reflects the existence of an interpersonal body representation (IBR) that allows us to represent the perceptual states and action possibilities of others. Here, we address the question of whether IBR can be modulated by higher level/reflective social cognition, such as judgments about one’s own social status. Participants responded with either the right or the left hand as soon as a go signal appeared. The go signal screen contained a task-irrelevant stimulus consisting of a 3D scene in which a mug with a left- or right-facing handle was positioned on a table. The mug was positioned either inside or outside the reaching space of the participants. In a third of the trials, the mug was positioned within the reaching space of an avatar seated at the table. Prior to this task we induced an experience of social ostracism in half of the participants by means of a standardized social exclusion condition. The results were that the SAE that normally occurs when the mug is in the avatar’s reaching space is extinguished by the induced social exclusion. This indicates that judgments about one’s own social status modulate the effect of IBR.     

Close to me: multisensory space representations for action and pre-reflexive consciousness of oneself-in-the-world

Philosophical considerations as well as several recent studies from neurophysiology, neuropsychology, and psychophysics converged in showing that the peripersonal space (i.e. closely surrounding the body-parts) is structured in a body-centred manner and represented through integrated sensory inputs. Multisensory representations may deserve the function of coding peripersonal space for avoiding or interacting with objects. Neuropsychological evidence is reviewed for dynamic interactions between space representations and action execution, as revealed by the behavioural effects that the use of a tool, as a physical extension of the reachable space, produces on visual-tactile extinction. In particular, tool-use transiently modifies action space representation in a functionally effective way. The possibility is discussed that the investigation of multisensory space representations for action provides an empirical way to consider in its specificity pre-reflexive self-consciousness by considering the intertwining of self-relatedness and object-directness of spatial experience shaped by multisensory and sensorimotor integrations.     

When far becomes near: Shared environments activate action simulation

It has been proposed that one means of understanding a person's current behaviour and predicting future actions is by simulating their actions. That is, when another person's actions are observed, similar motor processes are activated in the observer. For example, after observing a reach over an obstacle, a person's subsequent reach trajectory is more curved, reflecting motor priming. Importantly, such motor states are only activated if the observed action is in near (peripersonal) space. However, we demonstrate that when individuals share action environments, simulation of another person's obstacle avoiding reach path takes place even when the action is in far (extrapersonal) space. We propose that action simulation is influenced by factors such as ownership. When an “owned” object is a potential future obstacle, even when it is viewed beyond current action space, simulations are evoked, and these leave a more stable memory capable of influencing future behaviour.     

When objects are close to me: Affordances in the peripersonal space

In the present study, we investigated, using language, which motor information is automatically activated by observing 3-D objects (i.e., manipulation vs. function) and whether this information is modulated by the objects' location in space. Participants were shown 3-D pictures of objects located in peripersonal versus extrapersonal space. Immediately after, they were presented with function, manipulation, or observation verbs (e.g., "to drink," "to grasp," "to look at") and were required to judge whether the verb was compatible with the presented object. We found that participants were slower with observation verbs than with manipulation and function verbs. With both function and manipulation verbs, participants were faster when objects were presented in reachable space. Interestingly, the fastest response times were recorded when participants read function verbs while objects were presented in the accessible space. Results suggest that artifacts are first conceived in terms of affordances linked to manipulation and use, and that affordances are differently activated, depending on context.     

Rôle des propriétés inertielles segmentaires sur la perception de l’étendue de l’espace péripersonnel

Previous studies have suggested that the perception of peripersonal space can hardly be achieved using only scene-based visual cues and requires combining visual information with motor representations. Motor representation can be viewed as a component of a predictive system, which includes a neural process that simulates through motor imagery the dynamic behaviour of the body in relation to the environment. In this study, we analysed whether modifying the force required to reach a visual target influences the perception of what is reachable. In a visuomotor task, the experimental group (n = 10) adapted to a 1.5 kg weight attached to the right wrist while performing a series of pointing movements. The control group (n = 10) performed the motor task without inertial perturbation. A perceptual judgement task of what is reachable was performed before and after the motor task. Results showed that inertial perturbation produced initially an undershoot of the target suggesting a lack of motor force to overcome the inertial perturbation, but spatial errors receded progressively through movement rehearsal. Perceptual estimates of what is reachable slightly overestimated action capacities but were not affected by motor adaptation. Thus, modifying motor force required to compensate for inertial perturbation had no direct effect on the perception of peripersonal space. When interpreted in regard to previous experimental work, this result suggests that motor representations may provide information about the sensory or spatial consequences of action rather than the sense of effort associated with motor production.     

A question of intention in motor imagery

We examined the question—is the intention of completing a simulated motor action the same as the intention used in processing overt actions? Participants used motor imagery to estimate distance reachability in two conditions: Imagery-Only (IO) and Imagery-Execution (IE). With IO (red target) only a verbal estimate using imagery was given. With IE (green target) participants knew that they would actually reach after giving a verbal estimate and be judged on accuracy. After measuring actual maximum reach, used for the comparison, imagery targets were randomly presented across peripersonal- (within reach) and extrapersonal (beyond reach) space. Results indicated no difference in overall accuracy by condition, however, there was a significant distinction by space; participants were more accurate in peripersonal space. Although more research is needed, these findings support an increasing body of evidence suggesting that the neurocognitive processes (in this case, intention) driving motor imagery and overt actions are similar.     

Egocentric metric representations in peripersonal space: A bridge between motor resources and spatial memory

Research on visuospatial memory has shown that egocentric (subject-to-object) and allocentric (object-to-object) reference frames are connected to categorical (non-metric) and coordinate (metric) spatial relations, and that motor resources are recruited especially when processing spatial information in peripersonal (within arm reaching) than extrapersonal (outside arm reaching) space. In order to perform our daily-life activities, these spatial components cooperate along a continuum from recognition-related (e.g., recognizing stimuli) to action-related (e.g., reaching stimuli) purposes. Therefore, it is possible that some types of spatial representations rely more on action/motor processes than others. Here, we explored the role of motor resources in the combinations of these visuospatial memory components. A motor interference paradigm was adopted in which participants had their arms bent behind their back or free during a spatial memory task. This task consisted in memorizing triads of objects and then verbally judging what was the object: (1) closest to/farthest from the participant (egocentric coordinate); (2) to the right/left of the participant (egocentric categorical); (3) closest to/farthest from a target object (allocentric coordinate); and (4) on the right/left of a target object (allocentric categorical). The triads appeared in participants' peripersonal (Experiment 1) or extrapersonal (Experiment 2) space. The results of Experiment 1 showed that motor interference selectively damaged egocentric-coordinate judgements but not the other spatial combinations. The results of Experiment 2 showed that the interference effect disappeared when the objects were in the extrapersonal space. A third follow-up study using a within-subject design confirmed the overall pattern of results. Our findings provide evidence that motor resources play an important role in the combination of coordinate spatial relations and egocentric representations in peripersonal space.     

Priming of reach trajectory when observing actions: Hand-centred effects

When another person's actions are observed it appears that these actions are simulated, such that similar motor processes are triggered in the observer. Much evidence suggests that such simulation concerns the achievement of behavioural goals, such as grasping a particular object, and is less concerned with the specific nature of the action, such as the path the hand takes to reach the goal object. We demonstrate that when observing another person reach around an obstacle, an observer's subsequent reach has an increased curved trajectory, reflecting motor priming of reach path. This priming of reach trajectory via action observation can take place under a variety of circumstances: with or without a shared goal, and when the action is seen from a variety of perspectives. However, of most importance, the reach path priming effect is only evoked if the obstacle avoided by another person is within the action (peripersonal) space of the observer.     

Motor resources in peripersonal space are intrinsic to spatial encoding: Evidence from motor interference

The aim of this study was to explore the role of motor resources in peripersonal space encoding: are they intrinsic to spatial processes or due to action potentiality of objects? To answer this question, we disentangled the effects of motor resources on object manipulability and spatial processing in peripersonal and extrapersonal spaces. Participants had to localize manipulable and non-manipulable 3-D stimuli presented within peripersonal or extrapersonal spaces of an immersive virtual reality scenario. To assess the contribution of motor resources to the spatial task a motor interference paradigm was used. In Experiment 1, localization judgments were provided with the left hand while the right dominant arm could be free or blocked. Results showed that participants were faster and more accurate in localizing both manipulable and non-manipulable stimuli in peripersonal space with their arms free. On the other hand, in extrapersonal space there was no significant effect of motor interference. Experiment 2 replicated these results by using alternatively both hands to give the response and controlling the possible effect of the orientation of object handles. Overall, the pattern of results suggests that the encoding of peripersonal space involves motor processes per se, and not because of the presence of manipulable stimuli. It is argued that this motor grounding reflects the adaptive need of anticipating what may happen near the body and preparing to react in time.     

Affordances after spinal cord injury

Spinal cord injury can cause cognitive impairments even when no cerebral lesion is appreciable. As patients are forced to explore the environment in a non-canonical position (i.e., seated on a wheelchair), a modified relation with space can explain motor-related cognitive differences compared to non-injured individuals. Peripersonal space is encoded in motor terms, that is, in relation to the representation of action abilities and is strictly related to the affordance of reachability. In turn, affordances, the action possibilities suggested by relevant properties of the environment, are related to the perceiver's peripersonal space and motor abilities. One might suppose that these motor-related cognitive abilities are compromised when an individual loses the ability to move. We shed light on this issue in 10 patients with paraplegia and 20 matched controls. All have been administered an affordances-related reachability judgement task adapted from Costantini, Ambrosini, Tieri, Sinigaglia, and Committeri (2010, Experimental Brain Research, 207, 95) and neuropsychological tests. Our findings demonstrate that patients and controls show the same level of accuracy in estimating the location of their peripersonal space boundaries, but only controls show the typical overestimation of reaching range. Secondly, patients show a higher variability in their judgements than controls. Importantly, this finding is related to the patients’ ability to perform everyday tasks. Finally, patients are not faster in making their judgements on reachability in peripersonal space, while controls are. Our results suggest that not moving freely or as usual in the environment impact decoding of action-related properties even when the upper limbs are not compromised.     

Meditation alters representations of peripersonal space: Evidence from auditory evoked potentials

Meditation commonly gives rise to the feeling that the self and the surrounding world are no longer separate, as if the boundary between them has dissolved. We propose this may occur due to alterations in representations of peripersonal space (PPS), the reachable space surrounding the body which is integral to a sense of where one’s bodily “self” is located in space. Thirty-one participants completed an auditory oddball paradigm before and after a guided meditation, during which we measured their P3 evoked potential, a marker of attentional salience. Pre-meditation, participants exhibited an enhanced attentional response to stimuli presented within PPS, relative to beyond PPS. Post-meditation, this PPS attentional enhancement was negated, with no distinction between responses to stimuli within versus beyond PPS. The results suggest that meditation leads to a constriction of PPS boundaries, even in novice meditators, elucidating one potential cause of the perceptual changes associated with meditation.     

Depth perception in virtual reality: distance estimations in peri- and extrapersonal space.

The present study investigated depth perception in virtual environments. Twenty-three participants verbally estimated ten distances between 40 cm and 500 cm in three different virtual environments in two conditions: (1) only one target was presented or (2) ten targets were presented at the same time. Additionally, the presence of a metric aid was varied. A questionnaire assessed subjective ratings about physical complaints (e.g., headache), the experience in the virtual world (e.g., presence), and the experiment itself (self-evaluation of the estimations). Results show that participants underestimate the virtual distances but are able to perceive the distances in the right metric order even when only very simple virtual environments are presented. Furthermore, interindividual differences and intraindividual stabilities can be found among participants, and neither the three different virtual environments nor the metric aid improved depth estimations. Estimation performance is better in peripersonal than in extrapersonal space. In contrast, subjective ratings provide a preferred space: a closed room with visible floor, ceiling, and walls.     

Spatial limits on referred touch to an alien limb may reflect boundaries of visuo-tactile peripersonal space surrounding the hand

In this study, the spatial limits of referred touch to a rubber hand were investigated. Participants rated the strength of the perceived illusion when the rubber hand was placed in one of six different spatial positions (at a distance of 17.5-67.5cm horizontal from the participant's own hand). The results revealed a significant nonlinear relationship in the strength of the illusion, with the strongest ratings given when the two hands were closest; decaying significantly after a distance of 30cm. The time taken to elicit the illusion followed a similar trend. These results may reflect the response properties of bimodal visuo-tactile cells encoding peripersonal space around the hand.     

Crossing the pillars of hercules: The role of spatial frames of reference in error making

This paper introduces a perspective accounting for errors that may occur as a result of the human interaction with the three-dimensional (3D) space. Particularly, we are interested in errors that are caused by cognitively crossing the boundary between peripersonal and extrapersonal space. Several behavioural, neurophysiological, and neuropsychological perspectives are reviewed in order to develop the theoretical framework on which our ideas are founded. We argue that cognitively crossing the boundary implies switching from one frame of reference to another, which, as a consequence, implies specific costs. The results of five experiments (overall involving 76 participants) support our hypothesis, suggesting the existence of different action-oriented spatial frames of reference.     

Does how I look at what you're doing depend on what I'm doing?

Previous studies showed that people proactively gaze at the target of another's action by taking advantage of their own motor representation of that action. But just how selectively is one's own motor representation implicated in another's action processing? If people observe another's action while performing a compatible or an incompatible action themselves, will this impact on their gaze behaviour? We recorded proactive eye movements while participants observed an actor grasping small or large objects. The participants' right hand either freely rested on the table or held with a suitable grip a large or a small object, respectively. Proactivity of gaze behaviour significantly decreased when participants observed the actor reaching her target with a grip that was incompatible with respect to that used by them to hold the object in their own hand. This indicates that effective observation of action may depend on what one is actually doing, being actions observed best when the suitable motor representations may be readily recruited.