Exaggerating temporal differences enhances recognition of individuals from point light displays

Humans are very good at perceiving each other's movements. In this article, we investigate the role of time-based information in the recognition of individuals from point light biological motion sequences. We report an experiment in which we used an exaggeration technique that changes temporal properties while keeping spatial information constant; differences in the durations of motion segments are exaggerated relative to average values. Participants first learned to recognize six individuals on the basis of a simple, unexaggerated arm movement. Subsequently, they recognized positively exaggerated versions of those movements better than the originals. Absolute duration did not appear to be the critical cue. The results show that time-based cues are used for the recognition of movements and that exaggerating temporal differences improves performance. The results suggest that exaggeration may reflect general principles of how diagnostic information is encoded for recognition in different domains.     

The role of visual and nonvisual feedback in a vehicle steering task

This article investigates vehicle steering control, focusing on the task of lane changing and the role of different sources of sensory feedback. Participants carried out 2 experiments in a fully instrumented, motion-based simulator. Despite the high level of realism afforded by the simulator, participants were unable to complete a lane change in the absence of visual feedback. When asked to produce the steering movements required to change lanes and turn a corner, participants produced remarkably similar behavior in each case, revealing a misconception of how a lane-change maneuver is normally executed. Finally, participants were asked to change lanes in a fixed-based simulator, in the presence of intermittent visual information. Normal steering behavior could be restored using brief but suitably timed exposure to visual information. The data suggest that vehicle steering control can be characterized as a series of unidirectional, open-loop steering movements, each punctuated by a brief visual update.     

Visual guidance for hand advance but not hand withdrawal in a reach-to-eat task in adult humans: reaching is a composite movement

Many animal species use reaching for food to place in the mouth (reach-to-eat) with a hand, and it may be a primitive movement. Although researchers (I. Q. Whishaw, 2005; A. N. Iwaniuk & I. Q. Whishaw, 2000; M. Gentiluci, I. Toni, S. Chieffi, & G. Pavesi, 1994) have described visual guidance of reaching in both normal and brain-injured human and nonhuman primates, researchers have not described the contribution of vision during advance of the limb to grasp food and during withdrawal of the limb with food to the mouth. To evaluate visual contributions, the authors monitored eye movements in young adults as they reached for food with and without vision. Participants visually engaged the target prior to the 1st hand movement and disengaged it as the food was grasped. Visual occlusion slowed limb advance and altered digit shaping but did not affect withdrawal. The dependence on visual control of advance but not withdrawal suggests that the reach-to-eat movement is a composite of 2 basic movements under visual and tactile/proprioceptive guidance, respectively.     

The adaptation to sensory information in the production of bimanual movement patterns

Bimanual in-phase and anti-phase patterns were performed in the transverse plane under optimal and degraded proprioceptive conditions, i.e., without and with tendon vibration. Moreover, proprioceptive information was changed midway into each trial to examine on-line reorganization. In addition to the proprioceptive perturbation, the availability of visual information was manipulated to study to which degree sensory information from different modalities interact. Movement patterns performed under identical sensory conditions were compared, i.e., the first 15 s (control) and the 15 s following a change in afferent input (transfer). In the control and transfer conditions, movements with vibrations were less accurate than those without vibrations indicating the influence of optimal proprioceptive information in the calibration and recalibration of intrinsic bimanual movement patterns. Furthermore, pattern stability was affected by the nature of the transfer condition. This indicated that the degree of fluctuations in a sensory transfer situation depended upon the quality of the proprioceptive information experienced in the initial conditions. The influence of visual information was not without importance, although the nature of the coordination mode must be taken into account. In the control conditions, in-phase movements were less stable when vision was absent, whereas anti-phase movements were more stable when vision was not present. This observation was made independent of the available proprioceptive information revealing differences in visual guidance between both coordination modes. In the transfer conditions, pattern stability was similar during the vision and no-vision conditions suggesting a limited influence of visual information in the recalibration process.     

Effects of motor intention on the perception of somatosensory events: A behavioural and functional magnetic resonance imaging study

The intention to execute a movement can modulate our perception of sensory events, and this modulation is observed ahead of both ocular and upper limb movements. However, theoretical accounts of these effects, and also the empirical data, are often contradictory. Accounts of “active touch”, and the premotor theory of attention, have emphasized how movement intention leads to enhanced perceptual processing at the target of a movement, or on the to-be-moved effector. By contrast, recent theories of motor control emphasize how internal “forward” model (FM) estimates may be used to cancel or attenuate sensory signals that arise as a result of self-generated movements. We used behavioural and functional brain imaging (functional magnetic resonance imaging, fMRI) to investigate how perception of a somatosensory stimulus differed according to whether it was delivered to a hand that was about to execute a reaching movement or the alternative, nonmoving, hand. The results of our study demonstrate that a somatosensory stimulus delivered to a hand that is being prepared for movement is perceived to have occurred later than when that same stimulus is delivered to a nonmoving hand. This result indicates that it takes longer for a tactile stimulus to be detected when it is delivered to a moving limb and may correspond to a change in perceptual threshold. Our behavioural results are paralleled by the results of our fMRI study that demonstrated that there were significantly reduced blood-oxygen-level-dependent (BOLD) responses within the parietal operculum and insula following somatosensory stimulation of the hand being prepared for movement, compared to when an identical stimulus was delivered to a nonmoving hand. These findings are consistent with the prediction of FM accounts of motor control that postulate that central sensory suppression of somatosensation accompanies self-generated limb movements, and with previous reports indicating that effects of sensory suppression are observed in higher order somatosensory regions.     

Effects of motor intention on the perception of somatosensory events: a behavioural and functional magnetic resonance imaging study

The intention to execute a movement can modulate our perception of sensory events, and this modulation is observed ahead of both ocular and upper limb movements. However, theoretical accounts of these effects, and also the empirical data, are often contradictory. Accounts of "active touch", and the premotor theory of attention, have emphasized how movement intention leads to enhanced perceptual processing at the target of a movement, or on the to-be-moved effector. By contrast, recent theories of motor control emphasize how internal "forward" model (FM) estimates may be used to cancel or attenuate sensory signals that arise as a result of self-generated movements. We used behavioural and functional brain imaging (functional magnetic resonance imaging, fMRI) to investigate how perception of a somatosensory stimulus differed according to whether it was delivered to a hand that was about to execute a reaching movement or the alternative, nonmoving, hand. The results of our study demonstrate that a somatosensory stimulus delivered to a hand that is being prepared for movement is perceived to have occurred later than when that same stimulus is delivered to a nonmoving hand. This result indicates that it takes longer for a tactile stimulus to be detected when it is delivered to a moving limb and may correspond to a change in perceptual threshold. Our behavioural results are paralleled by the results of our fMRI study that demonstrated that there were significantly reduced blood-oxygen-level-dependent (BOLD) responses within the parietal operculum and insula following somatosensory stimulation of the hand being prepared for movement, compared to when an identical stimulus was delivered to a nonmoving hand. These findings are consistent with the prediction of FM accounts of motor control that postulate that central sensory suppression of somatosensation accompanies self-generated limb movements, and with previous reports indicating that effects of sensory suppression are observed in higher order somatosensory regions.     

Affordance-Based Control of Visually Guided Action

The purpose of this essay is to compare and contrast existing theoretical approaches to understanding the visual guidance of action and to introduce a new approach. The focus is on tasks, such as steering, braking, and intercepting, that are (more or less) continuously guided on the basis of visual information. The prominent approach, information-based control, captures important aspects of behavior but is incompatible with the theory of affordances, a core principle of the ecological approach. Information-based control also fails to capture how actors behave in ways that take the limits of their action capabilities into account. I attempt to resolve these problems by introducing a new approach, affordance-based control, which asserts that a primary function of vision is to allow actors to see the world in terms of what they can and cannot do. Affordance-based control captures the tight coupling between information in optic flow and movement that is characteristic of visually guided action but also provides a parsimonious explanation of how actors take into account the dynamic properties of their body and the environment.     

Reading Text Under Normal and Disappearing Presentation Conditions

InthispaperIwillsummariseaseriesofex鄄perimentsinwhichwe[1,2]investigatedwhetheritwaspossibletoinducea"gapeffect"duringreadingandtoexaminehowwellpeoplecanreadwhenthetextliterallydisappearsfrominfrontoftheireyes.Tocarryouttheworkwerecordedreaders'eyemovementsandemployedanovelsac鄄cadecontingentchangetechniqueinwhichwemadethewordthatthereaderwasfixatingdisap鄄pear60msafterfixationonset.Inadditiontoin鄄vestigatingwhetheragapeffectmightoccurduringreading,thisworkalsoinvestigatedwhethertheprimaryde…     

Creating number semantics through finger movement perception

Communication, language and conceptual knowledge related to concrete objects may rely on the sensory–motor systems from which they emerge. How abstract concepts can emerge from these systems is however still unknown. Here we report a functional interaction between a specific meaningful finger movement, such as a finger grip closing, and a concept as abstract as numerical magnitude. Participants were presented with Arabic digits to recall before or after they perceived a biological or non-biological hand movement. The results show that perceiving a grip closing slows down the processing of large magnitude numbers. Importantly, we show that this motor-to-semantic interaction differs from the reverse semantic-to-motor interaction, and that it does not result from a general movement amplitude processing as it is only observed for biological hand movements. These results demonstrate the functional link between number meaning and goal-directed finger movements, and show how abstract concept semantics can emerge from the sensory–motor circuits of the brain.     

Same kinematics but different objects during action observation: Detection times and motor evoked potentials

Motor resonance refers to the fact that an observed action is online subliminally reenacted. The aim of the present paper was to verify if, on equal terms of kinematics, the to-be-grasped object's intrinsic properties are influencing the observers' motor behaviour. A detection time and a single pulse transcranial magnetic stimulation experiment were performed to verify the effects of a change of object's intrinsic properties artificially made on a video showing a grasping action. In particular, the object substituting the original one was not graspable by the showed movement. Results indicated an influence of object's intrinsic properties: Detection times were delayed and motor evoked potentials were reduced when the movement shown was not suitable to grasp the object. These results are interpreted as an evidence that during grasping action observation the motor system of the observer is influenced not only by the seen movements but also by the to-be-grasped object.     

Obstacle avoidance under automated steering: Impact on driving and gaze behaviours

Within the context of more and more autonomous vehicles, an automatic lateral control device (AS: Automatic Steering) was used to steer the vehicle along the road without drivers’ intervention. The device was not able to detect and avoid obstacles. The experiment aimed to analyse unexpected obstacle avoidance manoeuvres when lateral control was delegated to automation. It was hypothesized that drivers skirting behaviours and eye movement patterns would be modified with automated steering compared with a control situation without automation. Eighteen participants took part in a driving simulator study. Steering behaviours and eye movements were analysed during obstacle avoidance episodes. Compared with driving without automation, skirting around obstacles was found to be less effective when drivers had to return from automatic steering to manual control. Eye movements were modified in the presence of automatic steering, revealing further ahead visual scanning of the driving environment. Resuming manual control is not only a problem of action performance but is also related to the reorganisation of drivers’ visual strategies linked to drivers’ disengagement from the steering task. Assistance designers should pay particular attention to potential changes in drivers’ activity when carrying out development work on highly automated vehicles.     

Sensory feedback in the learning of a novel motor task

The role of different forms of feedback is examined in learning a novel motor task. Five groups of ten subjects had to learn the voluntary control of the abduction of the big toe, each under a different feedback condition (proprioceptive feedback, visual feedback, EMG feedback, tactile feedback, force feedback). The task was selected for two reasons. First, in most motor learning studies subjects have to perform simple movements which present hardly any learning problem. Second, studying the learning of a new movement an provide useful information for neuromuscular reeducation, where patients often also have to learn movements for which no control strategy exists. The results show that artificial sensory feedback (EMG feedback, force feedback) is more powerful than "natural" (proprioceptive, visual, and tactile) feedback. The implications of these results for neuromuscular reeducation are discussed.     

Sensory Feedback in the Learning of a Novel Motor Task

The role of different forms of feedback is examined in learning a novel motor task. Five groups of ten subjects had to learn the voluntary control of the abduction of the big toe, each under a different feedback condition (proprioceptive feedback, visual feedback, EMG feedback, tactile feedback, force feedback). The task was selected for two reasons. First, in most motor learning studies subjects have to perform simple movements which present hardly any learning problem. Second, studying the learning of a new movement can provide useful information for neuromuscular reeducation, where patients often also have to learn movements for which no control strategy exists. The results show that artificial sensory feedback (EMG feedback, force feedback) is more powerful than “natural” (proprioceptive, visual, and tactile) feedback. The implications of these results for neuromuscular reeducation are discussed.     

Who is causing what? The sense of agency is relational and efferent-triggered

The sense of agency ("I did that") is a basic feature of our subjective experience. Experimental studies usually focus on either its attributional aspects (the "I" of "I did that") or on its motoric aspects (the "did" aspect of "I did that"). Here, we combine both aspects and focus on the subjective experience of the time between action and effect. Previous studies [Haggard, P., Aschersleben, G., Gehrke, J., & Prinz, W. (2002a). Action, binding and awareness. In W. Prinz, & B. Hommel (Eds.), Common mechanisms in perception and action: Attention and performance (Vol. XIX, pp. 266-285). Oxford: Oxford University Press] have shown a temporal attraction in the perceived times of actions and effects, but did directly not study the relation between them. In three experiments, time estimates of an interval between an action and its subsequent sensory effect were obtained. The actions were either voluntary key press actions performed by the participant or kinematically identical movements applied passively to the finger. The effects were either auditory or visual events or a passive movement induced to another finger. The results first indicated a shortening of the interval between one's own voluntary action and a subsequent effect, relative to passive movement conditions. Second, intervals initiated by observed movements, either of another person or of an inanimate object, were always perceived like those involving passive movements of one's own body, and never like those involving active movements. Third, this binding effect was comparable for auditory, somatic and visual effects of action. Our results provide the first direct evidence that agency involves a generalisable relation between actions and their consequences, and is triggered by efferent motor commands.     

Relative damping improves linear mass-spring models of goal-directed movements

A limitation of a simple linear mass-spring model in describing goal directed movements is that it generates rather slow movements when the parameters are kept within a realistic range. Does this imply that the control of fast movements cannot be approximated by a linear system? In servo-control theory, it has been proposed that an optimal controller should control movement velocity in addition to position. Instead of explicitly controlling the velocity, we propose to modify a simple linear mass-spring model. We replaced the damping relative to the environment (absolute damping) with damping with respect to the velocity of the equilibrium point (relative damping). This gives the limb a tendency to move as fast as the equilibrium point. We show that such extremely simple models can generate rapid single-joint movements. The resulting maximal movement velocities were almost equal to those of the equilibrium point, which provides a simple mechanism for the control of movement speed. We further show that peculiar experimental results, such as an 'N-shaped' equilibrium trajectory and the difficulties to measure damping in dynamic conditions, may result from fitting a model with absolute damping where one with relative damping would be more appropriate. Finally, we show that the model with relative damping can be used to model subtle differences between multi-joint interceptions. The model with relative damping fits the data much better than a version of the model with absolute damping.     

Active inference, sensory attenuation and illusions

Active inference provides a simple and neurobiologically plausible account of how action and perception are coupled in producing (Bayes) optimal behaviour. This can be seen most easily as minimising prediction error: we can either change our predictions to explain sensory input through perception. Alternatively, we can actively change sensory input to fulfil our predictions. In active inference, this action is mediated by classical reflex arcs that minimise proprioceptive prediction error created by descending proprioceptive predictions. However, this creates a conflict between action and perception; in that, self-generated movements require predictions to override the sensory evidence that one is not actually moving. However, ignoring sensory evidence means that externally generated sensations will not be perceived. Conversely, attending to (proprioceptive and somatosensory) sensations enables the detection of externally generated events but precludes generation of actions. This conflict can be resolved by attenuating the precision of sensory evidence during movement or, equivalently, attending away from the consequences of self-made acts. We propose that this Bayes optimal withdrawal of precise sensory evidence during movement is the cause of psychophysical sensory attenuation. Furthermore, it explains the force-matching illusion and reproduces empirical results almost exactly. Finally, if attenuation is removed, the force-matching illusion disappears and false (delusional) inferences about agency emerge. This is important, given the negative correlation between sensory attenuation and delusional beliefs in normal subjects—and the reduction in the magnitude of the illusion in schizophrenia. Active inference therefore links the neuromodulatory optimisation of precision to sensory attenuation and illusory phenomena during the attribution of agency in normal subjects. It also provides a functional account of deficits in syndromes characterised by false inference and impaired movement—like schizophrenia and Parkinsonism—syndromes that implicate abnormal modulatory neurotransmission.     

CARRYING THE BURDEN OF PAST VIOLENCES

Through a comparative study of two Palestinian transnational youth movements, this article seeks to understand how the transnational sphere traverses not just space but also time. I analyze how the Palestinian Youth Movement and the Gaza Youth Breaks Out movement understand themselves as carrying the burden of past violences in their promise to continue the Palestinian struggle and lead it toward a just and peaceful solution. Particularly, I am interested in how these movements interpret and conceive of the violences of 1948 and their continuation in present violences from different temporal, and not just spatial, standpoints. I examine the temporalities from which and to which transnational Palestinian movements speak, as well as how they orient themselves, through backward and forward movements, toward past–present–future. The article highlights how temporal differences form tensions that are often overlooked by transnational scholars and activists.     

A common first-order time-to-contact based control of hand-closure initiation in catching and grasping

To catch or grasp an object, the initiation of hand closure has to be coordinated with the relative movement between hand and object. In search of a common control of the initiation of hand closure for both tasks (van de Kamp, Bongers, & Zaal, 2010), the authors studied two tasks, catching while keeping the hand stationary and prehension. They showed that the initiation of hand closure could well be based on first-order time-to-contact in the prehension task but not in the catching task studied. The current study tested if the fact that the hand-object gap was closed at a linear rate made that the initiation of hand closure could not be explained on the basis of that same first-order time-to-contact in the catching task. In Experiment 1, the participants had to catch targets that approached at nonlinear rates while keeping the hand stationary. In Experiment 2, the participants were free to move their hand in catching the approaching objects, allowing the closure of the hand-object gap to occur at a nonlinear rate as it would in natural movements. The results showed that the first-order time-to-contact based control of the initiation of hand closure did apply in Experiment 2, whereas it did not in Experiment 1. It was concluded that constraining the catching task such that it became unfamiliar led to a hampered timing, thus obstructing the finding of the common control in the previous study, and in Experiment 1 of the current study.     

Action-dependent perceptual invariants: from ecological to sensorimotor approaches

Ecological and sensorimotor theories of perception build on the notion of action-dependent invariants as the basic structures underlying perceptual capacities. In this paper we contrast the assumptions these theories make on the nature of perceptual information modulated by action. By focusing on the question, how movement specifies perceptual information, we show that ecological and sensorimotor theories endorse substantially different views about the role of action in perception. In particular we argue that ecological invariants are characterized with reference to transformations produced in the sensory array by movement: such invariants are transformation-specific but do not imply motor-specificity. In contrast, sensorimotor theories assume that perceptual invariants are intrinsically tied to specific movements. We show that this difference leads to different empirical predictions and we submit that the distinction between motor equivalence and motor-specificity needs further clarification in order to provide a more constrained account of action/perception relations.     

Monocular and Binocular Vision in the Control of Goal-Directed Movement

In the present research the authors examined the time course of binocular integration in goal-directed aiming and grasping. With liquid-crystal goggles, the authors manipulated vision independently to the right and left eyes of 10 students during movement preparation and movement execution. Contrary to earlier findings reported in catching experiments (I. Olivier, D. J. Weeks, K. L. Ricker, J. Lyons, & D. Elliott, 1998), neither a temporal nor a spatial binocular advantage was obtained in 1 grasping and 2 aiming studies. That result suggests that, at least in some circumstances, monocular vision is sufficient for the precise control of limb movements. In a final aiming experiment involving 3-dimen- sional spatial variability and no trial-to-trial visual feedback about performance, binocular vision was associated with greater spatial accuracy. Binocular superiority appeared to be most pronounced when participants were unable to adjust their limb control strategy or procedure on the basis of terminal feedback about performance.