Reachability Judgement Research Articles

Active fault-tolerant control with prescribed performance and reachability judgement for the altitude ground test facility

This research proposes an active fault-tolerant control (AFTC) method based on reachability judgement with asymmetric appointed-time prescribed performance to ensure the safety of altitude ground test facility (AGTF) under potential valve actuator and sensor faults. Firstly, a long short-term memory (LSTM) neural network is employed for fault diagnosis. Given the unique characteristics of AGTF, the equivalent multiplicative fault is introduced to ensure the successful fitting of the fault diagnosis network. Then, a reachability judgement network based on the distance field on grids (DFOG) method is designed to assess the impact of faults on subsequent tasks of the system, thereby ensuring the safety of the AGTF. Subsequently, this study proposes an error transformation function of prescribed performance control (PPC) that ensures error convergence even in cases of asymmetric performance function. This enables the performance boundaries to be further reduced to improve the control performance of the system. Finally, experiments validate the effectiveness of the methods proposed in this manuscript.

The role of object ownership on online inhibition in peripersonal space.

Peripersonal space (PPS), as opposed to extrapersonal space (EPS), refers to the area surrounding the body within which individuals interact with objects or conspecifics. However, objects in PPS can belong to oneself or to others, which was found to influence how these objects are encoded. We analyzed the performances of motor responses in a reachability judgment task concerning self-owned and other-owned objects (cups) presented in PPS or EPS. EMG activities were recorded on the thumbs (flexor pollicis brevis) to detect correct and erroneous motor activations. Behavioral data showed that motor responses were shorter and longer for self-owned cups compared to other-owned cups in PPS and EPS, respectively. Ten percent of trials showed initial response errors, which were higher in the EPS for self-owned cups and in the PPS for other-owned cups. Eighty-two percent of these errors were corrected online, with corrections being more efficient for self-owned cups in the PPS. Overall, the data revealed that reachability judgments were faster and more accurate in the PPS, with more efficient inhibition processes in the presence of motor errors. Motor selection and correction are thus modulated by the social context of object ownership, highlighting the specific role of the PPS in encoding self-relevant objects for action.

Multisensory peripersonal space: Visual looming stimuli induce stronger response facilitation to tactile than auditory and visual stimulations

Anticipating physical contact with objects in the environment is a key component of efficient motor performance. Peripersonal neurons are thought to play a determinant role in these predictions by enhancing responses to touch when combined with visual stimuli in peripersonal space (PPS). However, recent research challenges the idea that this visuo-tactile integration contributing to the prediction of tactile events occurs strictly in PPS. We hypothesised that enhanced sensory sensitivity in a multisensory context involves not only contact anticipation but also heightened attention towards near-body visual stimuli. To test this hypothesis, Experiment 1 required participants to respond promptly to tactile (probing contact anticipation) and auditory (probing enhanced attention) stimulations presented at different moments of the trajectory of a (social and non-social) looming visual stimulus. Reduction in reaction time as compared to a unisensory baseline was observed from an egocentric distance of around 2 m (inside and outside PPS) for all multisensory conditions and types of visual stimuli. Experiment 2 tested whether these facilitation effects still occur in the absence of a multisensory context, i.e., in a visuo-visual condition. Overall, facilitation effects induced by the looming visual stimulus were comparable in the three sensory modalities outside PPS but were more pronounced for the tactile modality inside PPS (84 cm from the body as estimated by a reachability judgement task). Considered together, the results suggest that facilitation effects induced by visual looming stimuli in multimodal sensory processing rely on the combination of attentional factors and contact anticipation depending on their distance from the body.

Motor inhibition impacts the motor interference effect of dangerous objects based on a prime-target grasping consistency judgment task

Whether motor inhibition impacts the motor interference effect of dangerous objects is controversial. Previous studies have manipulated task type and found that dangerous objects elicited increased motor inhibition compared to safe objects in the reachability judgment task but not in the categorization task. However, it was still unclear why motor inhibition was reduced for dangerous objects in the categorization task. We speculated that the activation strength of object affordance might modulate the occurrence of motor inhibition. To test this hypothesis, the present study designed a prime-target grasping consistency judgment task and manipulated target grips (power grip vs. precision grip), target dangerousness (dangerous vs. safe), and Go/NoGo (Go vs. NoGo). The results showed that under the condition of high activation strength of the target affordance (i.e., power grip targets), processing dangerous targets evoked increased motor inhibition (reflected by a more negative frontal N2 component) compared to safe targets and produced a motor interference effect in reaction time (RT). In contrast, under the condition of low target affordance activation strength (i.e., precision grip targets), processing dangerous targets facilitated RT compared to safe targets, with no difference found between the dangerous and safe conditions in the frontal N2 component. Furthermore, compared to safe objects, dangerous objects attracted more attention and recruited more cognitive resources to select appropriate responses to them. This study extended the findings of previous studies on the motor interference effect by highlighting the importance of activation strength for eliciting motor inhibition based on the prime-target consistency judgment task.

Congruent action context releases Mu rhythm desynchronization when visual objects activate competing action representations.

Recent findings demonstrated that object perception is affected by the competition between action representations. Simultaneous activation of distinct structural ("grasp-to-move") and functional ("grasp-to-use") action representations slows down perceptual judgements on objects. At the brain level, competition reduces motor resonance effects during manipulable object perception, reflected by an extinction of μ rhythm desynchronization. However, how this competition is solved in the absence of object-directed action remains unclear. The present study investigates the role of context in the resolution of the competition between conflicting action representations during mere object perception. To this aim, thirty-eight volunteers were instructed to perform a reachability judgment task on 3D objects presented at different distances in a virtual environment. Objects were conflictual objects associated with distinct structural and functional action representations. Verbs were used to provide a neutral or congruent action context prior or after object presentation. Neurophysiological correlates of the competition between action representation were recorded using EEG. The main result showed a release of μ rhythm desynchronization when reachable conflictual objects were presented with a congruent action context. Context influenced μ rhythm desynchronization when the action context was provided prior or after object presentation in a time-window compatible with object-context integration (around 1000ms after the presentation of the first stimulus). These findings revealed that action context biases competition between co-activated action representations during mere object perception and demonstrated that μ rhythm desynchronization may be an index of activation but also competition between action representations in perception.

Object coding in peripersonal space depends on object ownership.

Previous studies have shown that objects located in the peripersonal space (PPS) receive enhanced attention, as compared with extrapersonal space (EPS), However, most objects in the environment belong to someone in particular and how object ownership influences object coding in relation to PPS representation is still unclear. In the present study, after having chosen their own mug, participants performed a reachability judgement task of self-owned and other-owned mugs presented at different distances while facing a virtual character. This task was followed, on each trial, by a localisation task in which participants had to indicate where the mug, removed from view, was previously located. The two tasks were separated by a 900-ms visual mask during which the virtual character was unnoticeably shifted by 3° to evaluate the spatial frame-of-reference used. The results showed that self-owned mugs were processed faster than other-owned mugs, but only when located in the PPS. Furthermore, reachability judgements were biased for self-owned mugs, leading to an extension of the PPS representation, especially for participants with a high score on the fantasy scale of Interpersonal Reactivity Index (IRI). Finally, the virtual character shift altered the localisation performance but only for the distant mugs, suggesting a progressive shift from egocentric to allocentric frame-of-reference when moving from the PPS to EPS, irrespective of object ownership. Overall, our data reveal that the representations of ownership and PPS interact to facilitate the processing of manipulable objects, to an extent that depends on individual sensitivity to the social presence of others.

Semi-Analytical Planetary Landing Guidance with Constraint Equations Using Model Predictive Control

With the deepening of planetary exploration, rapid decision making and descent trajectory planning capabilities are needed to cope with uncertain environmental disturbances and possible faults during planetary landings. In this article, a novel decoupling method is adopted, and the analytical three-dimensional constraint equations are derived and solved, ensuring real-time guidance computation. The three-dimensional motion modes and thrust profiles are analyzed and determined based on Pontryagin’s minimum principle, and a supporting semi-analytical reachability judgment method is presented, which can also be used to determine controllability. The algorithm is embedded in the model predictive control (MPC) framework, and several techniques are adopted to enhance stability and robustness, including thrust averaging, thrust correction after ignition, thrust reservation, and open-loop terminal guidance. Numerical simulations demonstrate that the proposed algorithm can guarantee real-time trajectory generation and meanwhile maintain considerable optimality. In addition, the MPC simulation shows that the algorithm can maintain a good accuracy under external disturbances.

Gradual exposure to Coriolis force induces sensorimotor adaptation with no change in peripersonal space

The space immediately surrounding the body is crucial for the organization of voluntary motor actions and seems to be functionally represented in the brain according to motor capacities. However, despite extensive research, little is known about how the representation of peripersonal space is adjusted to new action capacities. Abrupt exposure to a new force field has been shown to cause the representation of peripersonal space to shrink, possibly reflecting a conservative spatial strategy triggered by consciously-perceived motor errors. The present study assessed whether the representation of peripersonal space is influenced by gradual exposure of reaching movements to a new force field, produced by a stepwise acceleration of a rotating platform. We hypothesized that such gradual exposure would induce progressive sensorimotor adaptation to motor errors, albeit too small to be consciously perceived. In contrast, we hypothesized that reachability judgments, used as a proxy of peripersonal space representation, would not be significantly affected. Results showed that gradual exposure to Coriolis force produced a systematic after-effect on reaching movements but no significant change in reachability judgments. We speculate that the conscious experience of large motor errors may influence the updating of the representation of peripersonal space.

The Influence of Perceptual-Motor Variability on the Perception of Action Boundaries for Reaching in a Real-World Setting.

The ability to accurately perceive the extent over which one can act is requisite for the successful execution of visually guided actions. Yet, like other outcomes of perceptual-motor experience, our perceived action boundaries are not stagnant, but in constant flux. Hence, the perceptual systems must account for variability in one’s action capabilities in order for the perceiver to determine when they are capable of successfully performing an action. Recent work has found that, after reaching with a virtual arm that varied between short and long each time they reach, individuals determined their perceived action boundaries using the most liberal reaching experience. However, these studies were conducted in virtual reality, and the perceptual systems may handle variability differently in a real-world setting. To test this hypothesis, we created a modified orthopedic elbow brace that mimics injury in the upper limb by restricting elbow extension via remote control. Participants were asked to make reachability judgments after training in which the maximum extent of their reaching ability was either unconstricted, constricted or variable over several calibration trials. Findings from the current study did not conform to those in virtual reality; participants were more conservative with their reachability estimates after experiencing variability in a real-world setting.

Motor Inhibition to Dangerous Objects: Electrophysiological Evidence for Task-dependent Aversive Affordances.

Previous work suggests that perception of an object automatically facilitates actions related to object grasping and manipulation. Recently, the notion of automaticity has been challenged by behavioral studies suggesting that dangerous objects elicit aversive affordances that interfere with encoding of an object's motor properties; however, related EEG studies have provided little support for these claims. We sought EEG evidence that would support the operation of an inhibitory mechanism that interferes with the motor encoding of dangerous objects, and we investigated whether such mechanism would be modulated by the perceived distance of an object and the goal of a given task. EEGs were recorded by 24 participants who passively perceived dangerous and neutral objects in their peripersonal, boundary, or extrapersonal space and performed either a reachability judgment task or a categorization task. Our results showed that greater attention, reflected in the visual P1 potential, was drawn by dangerous and reachable objects. Crucially, a frontal N2 potential, associated with motor inhibition, was larger for dangerous objects only when participants performed a reachability judgment task. Furthermore, a larger parietal P3b potential for dangerous objects indicated the greater difficulty in linking a dangerous object to the appropriate response, especially when it was located in the participants' extrapersonal space. Taken together, our results show that perception of dangerous objects elicits aversive affordances in a task-dependent way and provides evidence for the operation of a neural mechanism that does not code affordances of dangerous objects automatically, but rather on the basis of contextual information.

Peripersonal space in social context is modulated by action reward, but differently in males and females.

The peripersonal space (PPS) is a multisensory representation of the near-body region of space where objects appear at hand. It also represents a buffer zone protecting the body from external threats and as such it contributes to the organization of social interactions. However, how the combination of embodied objects processing and constraints inherent to social interactions contributes to PPS representation remains an open issue. By using a cooperative task where two male (N = 22) or female (N = 18) participants, sharing the same action space, were requested to select a number of stimuli on a touch-screen table, we investigated the effect of non-uniform distribution of reward-yielding stimuli on selection strategy and perceptual judgments of reachability, used as a proxy of PPS representation. The probability to select a reward-yielding stimulus (50% of the stimuli) was 75% in the proximal space of one of the two confederates. Results showed that participants initially prioritized stimuli in their proximal space and were progressively influenced by the spatial distribution of reward-yielding stimuli, thus invading their confederate's action space when associated with higher probability of reward. The distribution of reward-yielding stimuli led to an increase of reachability threshold, but only when biased towards the participants' distal space. Although the invasion of others' PPS was more pronounced in male participants, the biased distribution of reward-yielding stimuli altered the reachability threshold similarly in males and females. As a whole, the data revealed that reward expectations in relation to motor actions influence both PPS exploration and representation in social context, but differently in males and females.

Reachable or Not? Perceptual judgments of reachability along the object-scene continuum

Reachable or Not? Perceptual judgments of reachability along the object-scene continuum

Can I reach it? A study in age-related macular degeneration and glaucoma patients

ABSTRACTAims: The visual exploration and the ability to correctly locate a target in reaching an object are critical in daily life. We investigate the object reachability judgment in neovascular age-related macular disease (nAMD) and primary open-angle glaucoma patients (POAG). Methods: Sixty-three participants were recruited in 4 groups (15 nAMD, 15 POAG, 18 old controls and 15 young controls). For each trial a cylinder moved between 11 random distances (from the border of their own peripersonal space 0, ±3, ±6, ±, ±12, ±15 cm). Participants had to estimate if they thought that the object was reachable or not. Results: POAG patients estimated that they could reach targets that were farther than their own peripersonal space (increased by 5.8 cm compared to the three other groups: 2.6 cm). The performance of the nAMD group and the normally sighted group were equivalent. Conclusions: The present study highlights the hypothesis of reach and grasps impairments in POAG due to difficulties in the estimation of reachability which is the beginning of any motor action processing. The reachability judgment of the nAMD patients is not affected. We conclude that POAG can modify the perceived peripersonal space of the patients and induce changes in the reachability judgment.

Sensori-motor adaptation to novel limb dynamics influences the representation of peripersonal space

Peripersonal space can be considered as the interface between the body and the environment, where objects can be reached and which may serve as a reference for the central nervous system with regard to possible actions. Peripersonal space can be studied by assessing the perception of the reachable space, which depends on the body's physical characteristics (i.e., arm length) since their modifications have been shown to be associated with a change in peripersonal space representation. However, it remains unclear whether the representation of limb dynamics also influences the representation of peripersonal space. The present study investigated this issue by perturbing the force-field environment. A novel force field was created by rotating an experimental platform where participants were seated while they reached towards visual targets. Manual reaching performance was assessed before, during and after platform rotation. Crucially, perception of peripersonal space was also assessed, with reachability judgments, before and after platform rotation. As expected, sensori-motor adaptation to the perturbed force field was observed. Our principal finding is that peripersonal space was systematically perceived as closer to the body after force-field adaptation. Two control experiments showed no significant difference in reachability judgments when no reaching movements were performed during platform rotation or when reaching movements were performed without platform rotation, suggesting that the change in perceived peripersonal space resulted from exposure to new limb dynamics. Overall, our findings show that sensori-motor adaptation of reaching movements to a new force field, which does not directly influence arm length but results in the updating of the arm's internal model of limb dynamics, interacts with the perceptual categorisation of space, supporting a motor contribution to the representation of peripersonal space.

Short-term upper-limb immobilization alters peripersonal space representation.

Peripersonal space is a multisensory interface between the environment and the body subserving motor interactions with the physical and social world. Although changing body properties has been shown to alter the functional processing of space, little is known about the effect of short-term limb immobilization specifically on the motor representation of peripersonal space. In the present study, we investigated the effect of a right upper-limb immobilization for a duration of 24h on a reachability judgment task and a brightness judgment task. Analyses of perceptual thresholds revealed a reduction of peripersonal space representation after the immobilization period, which was not observed when there was no immobilization (control group). In contrast, no variation appeared in the brightness judgment task, suggesting no presence of specific visual perception or decisional deficits in the limb immobilization group. Considered together, the results confirm the crucial role of the motor system in the representation of peripersonal space. They also highlight the plasticity of the motor system resulting in a rapid change of its activity following limb immobilization, with a concomitant effect on motor-related perceptual and cognitive processes.

Physiological Response to Facial Expressions in Peripersonal Space Determines Interpersonal Distance in a Social Interaction Context.

Accurate control of interpersonal distances in social contexts is an important determinant of effective social interactions. Although comfortable interpersonal distance seems to be dependent on social factors such as the gender, age and activity of the confederates, it also seems to be modulated by the way we represent our peripersonal-action space. To test this hypothesis, the present study investigated the relation between the emotional responses registered through electrodermal activity (EDA) triggered by human-like point-light displays (PLDs) carrying different facial expressions (neutral, angry, happy) when located in the participants peripersonal or extrapersonal space, and the comfort distance with the same PLDs when approaching and crossing the participants fronto-parallel axis on the right or left side. The results show an increase of the phasic EDA for PLDs with angry facial expressions located in the peripersonal space (reachability judgment task), in comparison to the same PLDs located in the extrapersonal space, which was not observed for PLDs with neutral or happy facial expressions. The results also show an increase of the comfort distance for PLDs approaching the participants with an angry facial expression (interpersonal comfort distance judgment task), in comparison to PLDs with happy and neutral ones, which was related to the increase of the physiological response. Overall, the findings indicate that comfort social space can be predicted from the emotional reaction triggered by a confederate when located within the observer’s peripersonal space. This suggests that peripersonal-action space and interpersonal-social space are similarly sensitive to the emotional valence of the confederate, which could reflect a common adaptive mechanism in specifying theses spaces to subtend interactions with both the physical and social environment, but also to ensure body protection from potential threats.

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.

Body-centred and Object-centred Motor Imagery in Alzheimer's Disease.

Autonomy in patients with Alzheimer's disease (AD) in daily life depends on the preservation of neurocognitive and motor abilities, which decline over time. So far, very few studies have investigated motor representations and their contribution to perception and cognition in AD. In the present study, we compared the performance of AD patients to age-matched healthy participants in perceptual and cognitive tasks involving motor imagery. Experiment 1 tested explicit motor and visual imagery through an imagined movement task. Experiment 2 tested body-centred implicit motor imagery through a mental rotation of visual hand task. Finally, Experiment 3 tested object-centred implicit motor imagery through a reachability judgment task. The results showed that, compared to age-matched controls, conscious imagination of a body movement or the movement of a visual stimulus was much longer in AD patients, with no specific difficulty in the motor condition (Experiment 1). Furthermore, response time in AD patients was strongly affected by the angle of rotation of the visual stimuli in the mental rotation of hand task (Experiment 2). Likewise, response time in AD patients increased substantially in the reachability judgment task, but predominantly for stimuli located at the boundary of peripersonal space (Experiment 3). As a whole, the data suggested a decline in AD of implicit, but not explicit, motor imagery capacities affecting processing time, but not performance accuracy, in motor-related perceptual and cognitive tasks.

Do Exploratory Arm Movements Contribute to Reach-Ability Judgments?

Gibson (1979/1986) argued that exploratory movements generate information about agents’ action-capabilities within a given environment, that is, about the agent-environment system’s affordances. To date, the scant literature on exploratory movements has revealed two important findings. First, restricting exploratory movements degrades the accuracy of affordance judgments (Mark et al., 1990; Yu, Bardy, & Stoffregen, 2011). Second, exploratory movements can be very subtle (Stoffregen, Yang, & Bardy, 2005; Yu, Bardy, & Stoffregen, 2011). However, many questions regarding exploratory movements have yet to be answered. For example, what exploratory movements are necessary to perceive a given affordance, and how do exploratory movements differ from related movements? Our long-term goal is to address such gaps in the literature. We decided to begin by examining what exploratory movements must be executed in order to perceive whether the actor can reach an object. Reaching exploratory movements likely have two key components: 1) head movements and 2) shoulder movements. The former can generate information about the absolute distance between the actor and the to-be-reached object (Bingham & Stassen, 1994), and have been confirmed to be necessary to produce accurate reaching judgments (Mantel, Stoffregen, Campbell & Bardy, 2015). The latter generates information about the actor’s arm length (Anderson & Turvey, 1998; Shibata, Gyoba, & Takeshima, 2012;), but their necessity to the reach-ability judgment has yet to be studied. The current experiment used a restriction paradigm to determine whether exploratory arm movements are necessary to make accurate reaching judgments. Participants (n = 32) judged their maximum reaching ability either while holding their arms behind their backs with their dominant hand grasping their non-dominant wrist (the Restricted condition), or while their arms swung naturally at their sides (the Unrestricted condition). Judgments were made actively, by walking forward or backward, in order to allow participants to generate the exploratory movements they would normally create (with the exception of arm movements in the Restricted condition) when moving toward an object with the intention to perform a reach (Mantel, Bardy, & Stoffregen, 2010). The study utilized a within-subjects design, with starting condition counterbalanced. For each condition, participants completed 1 practice trial followed by 9 experimental trials. Starting distances (from object) and angles were drawn equally and randomly from ranges of 1 – 24”, 25 – 48”, 49 – 72”, and 0 - 29o, 30 - 59o, 60 - 89o, respectively. Distances and angles were not repeated to prevent memorization. In line with previous affordance perception research, the dependent variable, Accuracy, was computed in terms of percentage of absolute error (|[judged maximum reach / actual maximum reach] -1| *100) (Oudejans, Michaels, Bakker, & Dolné, 1996). Accuracy was significantly greater when arm movements were unrestricted as compared to restricted, supporting the theory that exploratory arm movements are a component of reach-ability judgments. Reaching judgments in neither condition were perfectly accurate, which may have been due to the reaching judgment being the focal task (Heft, 1993). The present results have practical implications for operational situations in which actors’ arm movements might be restricted. For example, U.S. police and military personnel sometimes wear body armor that covers their shoulders, mounts ballistic plates to their upper arms, or some combination thereof. To the extent that such body armor restricts arm movements, then our results suggest that their reach-ability judgments would be degraded.

Reachability and the sense of embodiment in amputees using prostheses

Amputated patients are hardly satisfied with upper limb prostheses, and tend to favour the use of their contralateral arm to partially compensate their disability. This may seem surprising in light of recent evidences that external objects (rubber hand or tool) can easily be embodied, namely incorporated in the body representation. We investigated both implicit body representations (by evaluating the peripersonal space using a reachability judgement task) and the quality of bodily integration of the patient’s prosthesis (assessed via questionnaires). As expected, the patients estimated that they could reach further while wearing their prosthesis, showing an embodiment of their prosthesis in their judgement. Yet, the real reaching space was found to be smaller with their prosthesis than with their healthy limb, showing a large error between reachability judgement and actual capacity. An overestimation was also found on the healthy side (comparatively to healthy subjects) suggesting a bilateral modification of body representation in amputated patients. Finally, a correlation was found between the quality of integration of the prosthesis and the way the body representation changed. This study therefore illustrates the multifaceted nature of the phenomenon of prosthesis integration, which involves its incorporation as a tool, but also various specific subjective aspects.