Point-light Walkers Research Articles

Audiovisual integration increases the intentional step synchronization of side-by-side walkers

When people walk side-by-side, they often synchronize their steps. To achieve this, individuals might cross-modally match audiovisual signals from the movements of the partner and kinesthetic, cutaneous, visual and auditory signals from their own movements. Because signals from different sensory systems are processed with noise and asynchronously, the challenge of the CNS is to derive the best estimate based on this conflicting information. This is currently thought to be done by a mechanism operating as a Maximum Likelihood Estimator (MLE). The present work investigated whether audiovisual signals from the partner are integrated according to MLE in order to synchronize steps during walking. Three experiments were conducted in which the sensory cues from a walking partner were virtually simulated. In Experiment 1 seven participants were instructed to synchronize with human-sized Point Light Walkers and/or footstep sounds. Results revealed highest synchronization performance with auditory and audiovisual cues. This was quantified by the time to achieve synchronization and by synchronization variability. However, this auditory dominance effect might have been due to artifacts of the setup. Therefore, in Experiment 2 human-sized virtual mannequins were implemented. Also, audiovisual stimuli were rendered in real-time and thus were synchronous and co-localized. All four participants synchronized best with audiovisual cues. For three of the four participants results point toward their optimal integration consistent with the MLE model. Experiment 3 yielded performance decrements for all three participants when the cues were incongruent. Overall, these findings suggest that individuals might optimally integrate audiovisual cues to synchronize steps during side-by-side walking.

Natural Translating Locomotion Modulates Cortical Activity at Action Observation.

The present study verified if the translational component of locomotion modulated cortical activity recorded at action observation. Previous studies focusing on visual processing of biological motion mainly presented point light walker that were fixed on a spot, thus removing the net translation toward a goal that yet remains a critical feature of locomotor behavior. We hypothesized that if biological motion recognition relies on the transformation of seeing in doing and its expected sensory consequences, a significant effect of translation compared to centered displays on sensorimotor cortical activity is expected. To this aim, we explored whether EEG activity in the theta (4–8 Hz), alpha (8–12 Hz), beta 1 (14–20 Hz) and beta 2 (20–32 Hz) frequency bands exhibited selectivity as participants viewed four types of stimuli: a centered walker, a centered scrambled, a translating walker and a translating scrambled. We found higher theta synchronizations for observed stimulus with familiar shape. Higher power decreases in the beta 1 and beta 2 bands, indicating a stronger motor resonance was elicited by translating compared to centered stimuli. Finally, beta bands modulation in Superior Parietal areas showed that the translational component of locomotion induced greater motor resonance than human shape. Using a Multinomial Logistic Regression classifier we found that Dorsal-Parietal and Inferior-Frontal regions of interest (ROIs), constituting the core of action-observation system, were the only areas capable to discriminate all the four conditions, as reflected by beta activities. Our findings suggest that the embodiment elicited by an observed scenario is strongly mediated by horizontal body displacement.

Walking my way? Walker gender and display format Confounds the perception of specific emotions

Previous evidence has shown that males and females display different gait kinematics which may influence the perception of emotions displayed through the same walking gait. We therefore investigated the influence of walker gender on the perception of happiness, sadness, anger and fear displayed through walking movements. Full-light (FL), point-light (PL) and synthetically modelled point-light walkers (SW) of both genders were shown to perceivers over three experiments. Additionally, gender ambiguous synthetic walkers were shown to control for the influence of form, gender stereotypes and idiosyncratic gait movements on emotional gait perception. Each emotion was identified above chance level for both walker genders and in all display conditions though significantly less in PL and SW than in FL. The gender of the walker did not influence the pattern of identifications in FL walkers (Fear > Sad > Happy > Anger > Neutral), but did influence the identification patterns in PL (Female: [Happy = Sad = Fear = Anger] > Neutral; Male: Fear = Sad = [Happy > Anger] > Neutral) and SWs (Female: Happy = Sad = Anger = Fear = Neutral; Male: [Happy = Sad = Anger] > [Fear = Neutral]; Ambiguous: [[Happy = Sad = Anger] > Fear] = Neutral). The gender of the walker and format in which they are displayed influenced the perception of different basic emotions. The constructed SW stimuli also displayed happiness, sadness and anger with equivalent intensity in female, male and gender ambiguous walkers thus untangling the perception-expression entanglement that has plagued previous emotion perception research.

Emotion Recognition in Face and Body Motion in Bulimia Nervosa.

Social cognition has been studied extensively in anorexia nervosa (AN), but there are few studies in bulimia nervosa (BN). This study investigated the ability of people with BN to recognise emotions in ambiguous facial expressions and in body movement. Participants were 26 women with BN, who were compared with 35 with AN, and 42 healthy controls. Participants completed an emotion recognition task by using faces portraying blended emotions, along with a body emotion recognition task by using videos of point-light walkers. The results indicated that BN participants exhibited difficulties recognising disgust in less-ambiguous facial expressions, and a tendency to interpret non-angry faces as anger, compared with healthy controls. These difficulties were similar to those found in AN. There were no significant differences amongst the groups in body motion emotion recognition. The findings suggest that difficulties with disgust and anger recognition in facial expressions may be shared transdiagnostically in people with eating disorders. Copyright © 2017 John Wiley & Sons, Ltd and Eating Disorders Association.

Feature-based attentional tuning during biological motion detection measured with SSVEP.

Performance in detection tasks can be improved by directing attention to task-relevant features. In this study, we evaluate the direction tuning of selective attention to motion features when observers detect point-light biological motion in noise. Feature-based attention strategy is assessed by capitalizing on the sensitivity of unattended steady-state visual-evoked potential (SSVEP) to the spreading of feature-based attention to unattended regions of space. Participants monitored for the presence of a point-light walker embedded in uniform dynamic noise in the center of the screen. We analyzed the phase-locked electroencephalogram response to a flickering random-dot kinematogram (RDK) in an unattended peripheral annulus for the 1 s prior to the onset of the target. We found the highest SSVEP power to originate from electrodes over posterior parietal cortex (PPC), with power modulated by the direction of motion in the unattended annulus. The SSVEP was strongest on trials in which the unattended motion was opposite the facing direction of the walker, consistent with the backstroke of the feet and with the global direction of perceived background motion from a translating walker. Coherence between electrodes over PPC and other brain regions successfully predicted individual participant's d-prime, with the highest regression coefficients at electrodes over ventrolateral prefrontal cortex (VLPFC). The findings are evidence that functional connectivity between frontal and parietal cortex promote perceptual feature-based attention, and subsequent perceptual sensitivity, when segregating point-light figures from masking surround.

Impairments in the Visual Processing of Global Biological Motion Cues in Down Syndrome.

Down syndrome (DS) is one of the most common chromosomal disorders and is often associated with a number of motor and cognitive impairments. Little research has been dedicated to investigating the perceptual abilities of individuals with DS. The visual processing of biological motion has been shown to be impaired in DS. It has been proposed that these impairments may stem from an inability to process the global patterns of full-body motion produced by a moving actor; however, this has not been explicitly investigated. We tested groups of participants with and without DS on a task requiring the visual discrimination of point-light walkers from spatially scrambled versions of point-light walkers. Participants with DS demonstrated poorer performance and slower reaction times on the task than healthy controls. From these results, we conclude that biological motion processing is impaired in DS and that this deficit is related to an inability to integrate global configural cues. In a second experiment, individuals with DS were able to discriminate the direction in which laterally translating walkers moved, suggesting that the global motion processing deficit observed in Experiment 1 is specific to biological motion recognition and does not generalise to other types of global motion.

Our own action kinematics predict the perceived affective states of others.

Our movement kinematics provide useful cues about our affective states. Given that our experiences furnish models that help us to interpret our environment, and that a rich source of action experience comes from our own movements, in the present study, we examined whether we use models of our own action kinematics to make judgments about the affective states of others. For example, relative to one's typical kinematics, anger is associated with fast movements. Therefore, the extent to which we perceive anger in others may be determined by the degree to which their movements are faster than our own typical movements. We related participants' walking kinematics in a neutral context to their judgments of the affective states conveyed by observed point-light walkers (PLWs). As predicted, we found a linear relationship between one's own walking kinematics and affective state judgments, such that faster participants rated slower emotions more intensely relative to their ratings for faster emotions. This relationship was absent when observing PLWs where differences in velocity between affective states were removed. These findings suggest that perception of affective states in others is predicted by one's own movement kinematics, with important implications for perception of, and interaction with, those who move differently. (PsycINFO Database Record

First, you need a Gestalt: An interaction of bottom-up and top-down streams during the perception of the ambiguously rotating human walker

Our visual system combines sensory evidence with prior knowledge to produce a representation of an outside world. Here, we explored the limits of the feedforward computation using an ambiguously rotating human biological motion. Specifically, we investigated whether an overall rotation, which was added to all the displays used in the study, would be perceived when the point-light walker was presented upside-down, a condition that typically obliterates perception of a human Gestalt. We report that inversion of the point-light walker or the absence of an identifiable Gestalt abolished the perception of an overall rotation. Perception of rotation was restored if the human walker Gestalt could be identified (an upright walker), if observers were informed about the nature of the motion display, or if observers expected to see the rotation of an unknown dynamic object. This implies that a mathematically more complex human motion was accounted for before the remaining motion components could be used to infer an overall rotation. Our results indicate that the perceptual inference does not proceed in a hierarchical manner with the simpler components being identified first. Instead, prior knowledge acts as a starting point for the decomposition of an even relatively simple combination of two motions.

Biological motion distorts size perception

Visual illusions explore the limits of sensory processing and provide an ideal testbed to study perception. Size illusions – stimuli whose size is consistently misperceived – do not only result from sensory cues, but can also be induced by cognitive factors, such as social status. Here we investigate, whether the ecological relevance of biological motion can also distort perceived size. We asked observers to judge the size of point-light walkers (PLWs), configurations of dots whose movements induce the perception of human movement, and visually matched control stimuli (inverted PLWs). We find that upright PLWs are consistently judged as larger than inverted PLWs, while static point-light figures do not elicit the same effect. We also show the phenomenon using an indirect paradigm: observers judged the relative size of a disc that followed an inverted PLW larger than a disc following an upright PLW. We interpret this as a contrast effect: The upright PLW is perceived larger and thus the subsequent disc is judged smaller. Together, these results demonstrate that ecologically relevant biological-motion stimuli are perceived larger than visually matched control stimuli. Our findings present a novel case of illusory size perception, where ecological importance leads to a distorted perception of size.

Priming biological motion changes extrapersonal space categorization

Recent results have shown that the way we categorize space varies as a function of the frame of reference. If the reference frame (RF) is another person vs. an object, the distance is judged as reduced. It has been suggested that such an effect is due to the spontaneous processing of the other's motor potentialities. To investigate the impact of movement representation on space perception, we used biological motion displays as a prime for a spatial categorization task. In Exp. 1, participants were presented with a point-light walker or a scrambled motion, and then judged the location (“Near” or “Far”) of a target with a human body or an inanimate object as RF. In Exp. 2, participants were primed with point-light walkers of different speeds: a runner, a normal walker and a slow walker. In Exp. 3 they were primed with a point-light display depicting a human body sitting down on or standing up from a chair, with a human body RF either oriented or not oriented towards the target. Results showed a reduced judged distance when the human body RF was primed with a point-light walker (Exp. 1). Furthermore, we found an additional reduction of the judged distance when priming with a runner (Exp. 2). Finally, Exp. 3 showed that the human body RF has to be target oriented as a precondition for priming effects of the point-light walker.

Facilitating Effects of Emotion on the Perception of Biological Motion: Evidence for a Happiness Superiority Effect.

It has been reported that visual perception can be influenced not only by the physical features of a stimulus but also by the emotional valence of the stimulus, even without explicit emotion recognition. Some previous studies reported an anger superiority effect while others found a happiness superiority effect during visual perception. It thus remains unclear as to which emotion is more influential. In the present study, we conducted two experiments using biological motion (BM) stimuli to examine whether emotional valence of the stimuli would affect BM perception; and if so, whether a specific type of emotion is associated with a superiority effect. Point-light walkers with three emotion types (anger, happiness, and neutral) were used, and the threshold to detect BM within noise was measured in Experiment 1. Participants showed higher performance in detecting happy walkers compared with the angry and neutral walkers. Follow-up motion velocity analysis revealed that physical difference among the stimuli was not the main factor causing the effect. The results of the emotion recognition task in Experiment 2 also showed a happiness superiority effect, as in Experiment 1. These results show that emotional valence (happiness) of the stimuli can facilitate the processing of BM.

Biological motion distorts size perception

Visual illusions explore the limits of sensory processing and provide an ideal testbed to study perception. Size illusions - stimuli whose size is consistently misperceived - do not only result from sensory cues, but can also be induced by cognitive factors, such as social status. Here we investigate, whether the ecological relevance of biological motion can also distort perceived size. We asked observers to judge the size of point-light walkers (PLWs), configurations of dots whose movements induce the perception of human movement, and visually matched control stimuli (inverted PLWs). We find that upright PLWs are consistently judged as larger than inverted PLWs, while static point-light figures do not elicit the same effect. We also show the phenomenon using an indirect paradigm: observers judged the relative size of a disc that followed an inverted PLW larger than a disc following an upright PLW. We interpret this as a contrast effect: The upright PLW is perceived larger and thus the subsequent disc is judged smaller. Together, these results demonstrate that ecologically relevant biological-motion stimuli are perceived larger than visually matched control stimuli. Our findings present a novel case of illusory size perception, where ecological importance leads to a distorted perception of size.

Impaired perception of biological motion in Parkinson's disease.

We examined biological motion perception in Parkinson's disease (PD). Biological motion perception is related to one's own motor function and depends on the integrity of brain areas affected in PD, including posterior superior temporal sulcus. If deficits in biological motion perception exist, they may be specific to perceiving natural/fast walking patterns that individuals with PD can no longer perform, and may correlate with disease-related motor dysfunction. Twenty-six nondemented individuals with PD and 24 control participants viewed videos of point-light walkers and scrambled versions that served as foils, and indicated whether each video depicted a human walking. Point-light walkers varied by gait type (natural, parkinsonian) and speed (0.5, 1.0, 1.5 m/s). Participants also completed control tasks (object motion, coherent motion perception), a contrast sensitivity assessment, and a walking assessment. The PD group demonstrated significantly less sensitivity to biological motion than the control group (p < .001, Cohen's d = 1.22), regardless of stimulus gait type or speed, with a less substantial deficit in object motion perception (p = .02, Cohen's d = .68). There was no group difference in coherent motion perception. Although individuals with PD had slower walking speed and shorter stride length than control participants, gait parameters did not correlate with biological motion perception. Contrast sensitivity and coherent motion perception also did not correlate with biological motion perception. PD leads to a deficit in perceiving biological motion, which is independent of gait dysfunction and low-level vision changes, and may therefore arise from difficulty perceptually integrating form and motion cues in posterior superior temporal sulcus. (PsycINFO Database Record

SSVEP captures predictive feature-based attentional tuning for point-light biological walker detection in unattended spatial locations

SSVEP captures predictive feature-based attentional tuning for point-light biological walker detection in unattended spatial locations

Constraint-based hierarchical motion analysis for biological movements

Movements of the human body are comprised of multiple motion components organized in a hierarchical manner. For example, the motion of a foot joint is nested within a moving leg, which is nested within a moving body. It remains unknown how humans discover the hierarchical structure representing bodily movements, and what fundamental constraints underlie the formation of motion structure. A non-parametric Bayesian model was developed to infer the hierarchical motion structures that can generate observed visual input. Many different hierarchical motion structures would be consistent with observed bodily movements, but three types of constraints sufficed to resolve ambiguity: a generic prior on object parsing (favoring simpler hierarchical structures), a generic prior on spatially smooth motion within a component (resulting from rigid movements of individual parts), and a body-specific constraint (certain joints move in coordination based on body structure). This generative model can account for a range of findings in the literature on biological motion perception, including better recognition performance for an upright than an inverted point-light walker, above-chance performance in discriminating walking direction for a spatially-scrambled and phase-scrambled walker (Troje & Westhoff, 2006, Exp. 2), the special contribution of foot movements in discriminating walking direction (Troje & Westhoff, 2006, Exp. 3), the variation in recognition accuracy across different action categories (Dittrich, 1993). The model also reveals how body structure interacts with the organization of motion components to form efficient action representations. When the body constraint was included in the formation of hierarchical structure, the representation space of actions was altered to cluster similar action types, but enlarge the distances of different actions. This finding suggests that the body constraint plays an important role in organizing motion information into a hierarchical structure, thereby increasing the representational power of an action space. Meeting abstract presented at VSS 2016

Do income and psychosomatic health predict adult sociosexual behaviors? Results from a Japanese sample

Strategic pluralism suggests that women engage in short-term sexual relationships when the benefits to doing so outweigh the costs. We investigated attraction to indicators of good genes (namely, masculinity as demonstrated by point-light walkers) in women varying in menstrual cycle status and sociosexual orientation. When women are fertile, they have the ability to gain genetic benefits from a male partner and should also be attracted to high levels of masculinity in men as a signal of genetic benefits. Sociosexual orientation is an individual difference that indicates openness to short-term mating and, thus, should influence aspects of mating strategy. Women with an unrestricted sociosexual orientation, as compared to women with a restricted sociosexual orientation, are more likely to engage in short-term relationships and obtain fewer nongenetic resources from their mates. Thus, they should place heavy emphasis on male masculinity as a sign of genetic benefits available from their mates. In this study, women indicated the walker most attractive to them on a constructed continuum of male and female point-light walkers. In Study 1, fertile women, as compared to nonfertile women, showed a greater attraction to masculinity. In Study 2, women demonstrated a strong positive relationship between sociosexuality and attraction to masculinity.

Keeping you at arm's length: modifying peripersonal space influences interpersonal distance.

Peripersonal space represents the area around the body where objects are coded in motor terms for the purpose of voluntary goal-directed actions. Previous studies have suggested that peripersonal space is also a safe space linked with our private area, influencing interpersonal space in social contexts. However, whether these two spaces rely on similar embodied processes remains an open issue. In the present study, participants observed a point-light walker (PLW) approaching them from different directions and passing near them at different distances from their right or left shoulder. While approaching, the PLW disappeared at a distance of 2m and the task for the participants was to estimate if the interpersonal distance, at the time the PLW would have reached their level, was comfortable or not. Between two sessions of comfort judgments, the participants manipulated a 70cm tool entailing an extension of peripersonal space, or a 10cm tool entailing no extension of peripersonal space. The results revealed that the comfortable interpersonal distance was larger when the PLW crossed the mid-sagittal plane of the participants than when it approached them laterally, with a concomitant increase of response time. After participants manipulated the long tool, comfortable interpersonal distance increased, but predominantly when the PLW trajectory implied crossing the participants' mid-sagittal plane. This effect was not observed when participants manipulated the short tool. Two control tasks showed that using the long tool modified the reachability (control 1), but not the time to passage (control 2) estimates of PLW stimuli, suggesting that tool use extended peripersonal space without changing perceived visual distances. Overall, the data show that comfortable interpersonal distance is linked to the representation of peripersonal space. As a consequence, increasing peripersonal space through tool use has the immediate consequence that comfortable interpersonal distance from another person also increases, suggesting that interpersonal-comfort space and peripersonal-reaching space share a common motor nature.

Global form and motion processing in healthy ageing

The ability to perceive biological motion has been shown to deteriorate with age, and it is assumed that older adults rely more on the global form than local motion information when processing point-light walkers. Further, it has been suggested that biological motion processing in ageing is related to a form-based global processing bias. Here, we investigated the relationship between older adults' preference for form information when processing point-light actions and an age-related form-based global processing bias. In a first task, we asked older (>60years) and younger adults (19–23years) to sequentially match three different point-light actions; normal actions that contained local motion and global form information, scrambled actions that contained primarily local motion information, and random-position actions that contained primarily global form information. Both age groups overall performed above chance in all three conditions, and were more accurate for actions that contained global form information. For random-position actions, older adults were less accurate than younger adults but there was no age-difference for normal or scrambled actions. These results indicate that both age groups rely more on global form than local motion to match point-light actions, but can use local motion on its own to match point-light actions. In a second task, we investigated form-based global processing biases using the Navon task. In general, participants were better at discriminating the local letters but faster at discriminating global letters. Correlations showed that there was no significant linear relationship between performance in the Navon task and biological motion processing, which suggests that processing biases in form- and motion-based tasks are unrelated.

Local form interference in biological motion perception.

Replacing the local dots of point-light walkers with complex images leads to significant detriments to performance in biological motion detection and discrimination tasks. This detriment has previously been shown to be larger when the local elements match the global shape in object category and facing direction. In contrast, studies using Navon stimuli have demonstrated that local interference on global processing primarily occurs when local elements are dissimilar to the global form. In 3 experiments, we investigated this contradiction by replacing the local dots of a point-light walker with human images or stick figures. Participants were significantly faster and more accurate at discriminating the facing and walking direction of a walker when the local images were facing in the same direction as the global walker than when they were facing in the opposite direction. These results provide support for the idea that organization of biological motion depends on allocation of limited processing resources to the global motion information when the local elements are complex. However, there is more disruption to global form processing when the local elements and global form conflict in task-related properties.

Disappearance of the inversion effect during memory-guided tracking of scrambled biological motion.

The human visual system is highly sensitive to biological motion. Even when a point-light walker is temporarily occluded from view by other objects, our eyes are still able to maintain tracking continuity. To investigate how the visual system establishes a correspondence between the biological-motion stimuli visible before and after the disruption, we used the occlusion paradigm with biological-motion stimuli that were intact or scrambled. The results showed that during visually guided tracking, both the observers' predicted times and predictive smooth pursuit were more accurate for upright biological motion (intact and scrambled) than for inverted biological motion. During memory-guided tracking, however, the processing advantage for upright as compared with inverted biological motion was not found in the scrambled condition, but in the intact condition only. This suggests that spatial location information alone is not sufficient to build and maintain the representational continuity of the biological motion across the occlusion, and that the object identity may act as an important information source in visual tracking. The inversion effect disappeared when the scrambled biological motion was occluded, which indicates that when biological motion is temporarily occluded and there is a complete absence of visual feedback signals, an oculomotor prediction is executed to maintain the tracking continuity, which is established not only by updating the target's spatial location, but also by the retrieval of identity information stored in long-term memory.