Biological Motion Research Articles

Illusory percepts of curvilinear self-motion when moving through crowds.

Self-motion generates optic flow, a pattern of expanding visual motion. Heading estimation from optic flow analysis is accurate in rigid environments, but it becomes challenging when other human walkers introduce independent motion to the scene. Previous studies showed that heading perception is surprisingly accurate when moving through a crowd of walkers but revealed strong heading biases when either articulation or translation of biological motion were presented in isolation. We hypothesized that these biases resulted from misperceiving the self-motion as curvilinear. Such errors might manifest as opposite biases depending on whether the observer perceived the crowd motion as indication of his/her self-translation or self-rotation. Our study investigated the link between heading biases and illusory path perception. Participants assessed heading and path perception while observing optic flow stimuli with varying walker movements. Self-motion perception was accurate during natural locomotion (articulation and translation), but significant heading biases occurred when walkers only articulated or translated. In this case, participants often reported a curved path of travel. Heading error and curvature pointed in opposite directions. On average, participants perceived the walker motion as evidence for viewpoint rotation leading to curvilinear path percepts.

A neurophysiological signature of dynamic emotion recognition associated with social communication skills and cortical gamma-aminobutyric acid levels in children.

Emotion recognition is a core feature of social perception. In particular, perception of dynamic facial emotional expressions is a major feature of the third visual pathway. However, the classical N170 visual evoked signal does not provide a pure correlate of such processing. Indeed, independent component analysis has demonstrated that the N170 component is already active at the time of the P100, and is therefore distorted by early components. Here we implemented, a dynamic face emotional paradigm to isolate a more pure face expression selective N170. We searched for a neural correlate of perception of dynamic facial emotional expressions, by starting with a face baseline from which a facial expression evolved. This allowed for a specific facial expression contrast signal which we aimed to relate with social communication abilities and cortical gamma-aminobutyric acid (GABA) levels. We recorded event-related potentials (ERPs) and Magnetic Resonance (MRS) measures in 35 typically developing (TD) children, (10-16 years) sex-matched, during emotion recognition of an avatar morphing/unmorphing from neutral to happy/sad expressions. This task allowed for the elimination of the contribution low-level visual components, in particular the P100, by morphing baseline isoluminant neutral faces into specific expressions, isolating dynamic emotion recognition. Therefore, it was possible to isolate a dynamic face sensitive N170 devoid of interactions with earlier components. We found delayed N170 and P300, with a hysteresis type of dependence on stimulus trajectory (morphing/unmorphing), with hemispheric lateralization. The delayed N170 is generated by an extrastriate source, which can be related to the third visual pathway specialized in biological motion processing. GABA levels in visual cortex were related with N170 amplitude and latency and predictive of worse social communication performance (SCQ scores). N170 latencies reflected delayed processing speed of emotional expressions and related to worse social communication scores. In sum, we found a specific N170 electrophysiological signature of dynamic face processing related to social communication abilities and cortical GABA levels. These findings have potential clinical significance supporting the hypothesis of a spectrum of social communication abilities and the identification of a specific face-expression sensitive N170 which can potentially be used in the development of diagnostic and intervention tools.

Brain oscillations in reflecting motor status and recovery induced by action observation-driven robotic hand intervention in chronic stroke.

Hand rehabilitation in chronic stroke remains challenging, and finding markers that could reflect motor function would help to understand and evaluate the therapy and recovery. The present study explored whether brain oscillations in different electroencephalogram (EEG) bands could indicate the motor status and recovery induced by action observation-driven brain-computer interface (AO-BCI) robotic therapy in chronic stroke. The neurophysiological data of 16 chronic stroke patients who received 20-session BCI hand training is the basis of the study presented here. Resting-state EEG was recorded during the observation of non-biological movements, while task-stage EEG was recorded during the observation of biological movements in training. The motor performance was evaluated using the Action Research Arm Test (ARAT) and upper extremity Fugl-Meyer Assessment (FMA), and significant improvements (p < 0.05) on both scales were found in patients after the intervention. Averaged EEG band power in the affected hemisphere presented negative correlations with scales pre-training; however, no significant correlations (p > 0.01) were found both in the pre-training and post-training stages. After comparing the variation of oscillations over training, we found patients with good and poor recovery presented different trends in delta, low-beta, and high-beta variations, and only patients with good recovery presented significant changes in EEG band power after training (delta band, p < 0.01). Importantly, motor improvements in ARAT correlate significantly with task EEG power changes (low-beta, c.c = 0.71, p = 0.005; high-beta, c.c = 0.71, p = 0.004) and task/rest EEG power ratio changes (delta, c.c = -0.738, p = 0.003; low-beta, c.c = 0.67, p = 0.009; high-beta, c.c = 0.839, p = 0.000). These results suggest that, in chronic stroke, EEG band power may not be a good indicator of motor status. However, ipsilesional oscillation changes in the delta and beta bands provide potential biomarkers related to the therapeutic-induced improvement of motor function in effective BCI intervention, which may be useful in understanding the brain plasticity changes and contribute to evaluating therapy and recovery in chronic-stage motor rehabilitation.

The effects of temporal cues, point-light displays, and faces on speech identification and listening effort.

Among the most robust findings in speech research is that the presence of a talking face improves the intelligibility of spoken language. Talking faces supplement the auditory signal by providing fine phonetic cues based on the placement of the articulators, as well as temporal cues to when speech is occurring. In this study, we varied the amount of information contained in the visual signal, ranging from temporal information alone to a natural talking face. Participants were presented with spoken sentences in energetic or informational masking in four different visual conditions: audio-only, a modulating circle providing temporal cues to salient features of the speech, a digitally rendered point-light display showing lip movement, and a natural talking face. We assessed both sentence identification accuracy and self-reported listening effort. Audiovisual benefit for intelligibility was observed for the natural face in both informational and energetic masking, but the digitally rendered point-light display only provided benefit in energetic masking. Intelligibility for speech accompanied by the modulating circle did not differ from the audio-only conditions in either masker type. Thus, the temporal cues used here were insufficient to improve speech intelligibility in noise, but some types of digital point-light displays may contain enough phonetic detail to produce modest improvements in speech identification in noise.

Performance of additively manufactured Ti6Al4V ELI finger joints: biomechanical testing and evaluation for arthritis management

Abstract Approximately 24 out of every 100 adults in the United States, or 58.5 million people, have arthritis, which refers to a condition that causes pain and inflammation in a joint according to US National Center for Chronic Disease Prevention and Health Promotion. Osteoarthritis is the most common type of arthritis, and it may damage almost any joint but mainly occur in hands, hips and knees. While there are several joint replacement options for hips and knees, there are only limited options for finger joints. In this paper, we report on several aspects of testing of novel finger joints: testing apparatus design, cadaveric performance test and material testing results of titanium joints using 3D-printed Ti6Al4V extra low interstitial (ELI). Soft cadaveric hands with finger joints were surgically replaced by additively manufactured titanium joints following the exact same anatomy of the cadavers. These small joints were engineered to mimic the biological and natural movements of fingers. The apparatus, methodology and results of biomechanical tests were deployed to evaluate and validate the joints particularly those of titanium joints manufactured via laser powder bed fusion methods (PBF-L/M).

Hysteresis reveals a happiness bias effect in dynamic emotion recognition from ambiguous biological motion.

Considering the nonlinear dynamic nature of emotion recognition, it is believed to be strongly dependent on temporal context. This can be investigated by resorting to the phenomenon of hysteresis, which features a form of serial dependence, entailed by continuous temporal stimulus trajectories. Under positive hysteresis, the percept remains stable in visual memory (persistence) while in negative hysteresis, it shifts earlier (adaptation) to the opposite interpretation. Here, we asked whether positive or negative hysteresis occurs in emotion recognition of inherently ambiguous biological motion, while testing for the controversial debate of a negative versus positive emotional bias. Participants (n = 22) performed a psychophysical experiment in which they were asked to judge stimulus transitions between two emotions, happiness and sadness, from an actor database, and report perceived emotion across time, from one emotion to the opposite as physical cues were continuously changing. Our results reveal perceptual hysteresis in ambiguous emotion recognition, with positive hysteresis (visual persistence) predominating. However, negative hysteresis (adaptation/fatigue) was also observed in particular in the direction from sadness to happiness. This demonstrates a positive (happiness) bias in emotion recognition in ambiguous biological motion recognition. Finally, the interplay between positive and negative hysteresis suggests an underlying competition between visual persistence and adaptation mechanisms during ambiguous emotion recognition.

Simultaneous Sensing and Actuating Capabilities of a Triple-Layer Biomimetic Muscle for Soft Robotics.

This work presents the fabrication and characterization of a triple-layered biomimetic muscle constituted by polypyrrole (PPy)-dodecylbenzenesulfonate (DBS)/adhesive tape/PPy-DBS demonstrating simultaneous sensing and actuation capabilities. The muscle was controlled by a neurobiologically inspired cortical neural network sending agonist and antagonist signals to the conducting polymeric layers. Experiments consisted of controlled voluntary movements of the free end of the muscle at angles of ±20°, ±30°, and ±40° while monitoring the muscle's potential response. Results show the muscle's potential varies linearly with applied current amplitude during actuation, enabling current sensing. A linear dependence between muscle potential and temperature enabled temperature sensing. Electrolyte concentration changes also induced exponential variations in the muscle's potential, allowing for concentration sensing. Additionally, the influence of the electric current density on the angular velocity, the electric charge density, and the desired angle was studied. Overall, the conducting polymer-based soft biomimetic muscle replicates properties of natural muscles, permitting simultaneous motion control, current, temperature, and concentration sensing. The integrated neural control system exhibits key features of biological motion regulation. This muscle actuator with its integrated sensing and control represents an advance for soft robotics, prosthetics, and biomedical devices requiring biomimetic multifunctionality.

Skill and experience impact neural activity during global and local biological motion processing

During biological motion perception, individuals with perceptual experience learn to use more global processing, simultaneously extracting information from multiple body segments. Less experienced observers may use more local processing of individual body segments. The parietal lobe (e.g., alpha and beta power) has been shown to be critical to global and local static stimulus perception. Therefore, in this paper, we examined how skill impacts motion processing by assessing behavioral and neural responses to degrading global or local motion information for soccer penalty kicks. Skilled (N = 21) and less skilled (N = 19) soccer players anticipated temporally occluded videos of penalty kicks under normal, blurred (degraded local information), or spatially occluded (hips-only; degraded global information) viewing conditions. EEG was used to measure parietal alpha and beta power. Skilled players outperformed less skilled players, albeit both skill groups were less accurate in the blurred and hips-only conditions. Skilled performers showed significant decreases in bilateral parietal beta power in the hips-only condition, suggesting a greater reliance on global motion information under normal viewing conditions. Additionally, the hips-only condition elicited significantly greater beta relative to alpha power (beta – alpha), lower beta power, and lower alpha power than the control condition for both skill groups, suggesting spatial occlusion elicited a shift towards more local processing. Our novel findings demonstrate that skill and experience impact how motion is processed.

Neural processing of bottom-up perception of biological motion under attentional load

Considering its importance for one’s survival and social significance, biological motion (BM) perception is assumed to occur automatically. Previous behavioral results showed that task-irrelevant BM in the periphery interfered with task performance at the fovea. Under selective attention, BM perception is supported by a network of regions including the occipito-temporal (OTC), parietal, and premotor cortices. Retinotopy studies that use BM stimulus showed distinct maps for its processing under and away from selective attention. Based on these findings, we investigated how bottom-up perception of BM would be processed in the human brain under attentional load when it was shown away from the focus of attention as a task-irrelevant stimulus. Participants (N = 31) underwent an fMRI study in which they performed an attentionally demanding visual detection task at the fovea while intact or scrambled point light displays of BM were shown at the periphery. Our results showed the main effect of attentional load in fronto-parietal regions and both univariate activity maps and multivariate pattern analysis results support the attentional load modulation on the task-irrelevant peripheral stimuli. However, this effect was not specific to intact BM stimuli and was generalized to motion stimuli as evidenced by the motion-sensitive OTC involvement during the presence of dynamic stimuli in the periphery. These results confirm and extend previous work by showing that task-irrelevant distractors can be processed by stimulus-specific regions when there are enough attentional resources available. We discussed the implications of these results for future studies.

Effects of Different Motion Parameters on the Interaction of Fish School Subsystems.

For a long time, fish school swimming has attracted a great deal of attention in biological systems, as fish schools can have complex hydrodynamic effects on individuals. This work adopted a non-iterative, immersed boundary-lattice Boltzmann method (IB-LBM). A numerical simulation of two-dimensional three-degree-of-freedom self-propelled fish, in side-by-side, staggered, and triangle formations, was conducted by adjusting spacing and motion parameters. A comprehensive analysis of individual speed gains and energy efficiencies in these formations was carried out. Furthermore, an analysis of the hydrodynamic characteristics of fish schools was performed, using instantaneous vorticity profiles and pressure fields. Certain studies have shown that passive interactions between individuals cannot always bring hydrodynamic benefits. The swimming efficiency of side-by-side formations in the same phase gradually increases as the distance decreases, but it also brings certain burdens to individuals when the phases are different. This paper also shows that the roles of passive interactions, spacing, and deflections affect fish school subsystems differently. When the low-pressure areas created by a wake vortex act on one side of an individual's body, the tail-end fish are good at gaining hydrodynamic benefits from it. This effect is not universal, and the degree to which individuals benefit from changes in exercise parameters varies. This study provides a theoretical basis for bioinspired robots, as well as providing certain insights into the mechanism of collective biological movement.

Newborns' perception of approach and withdrawal from biological movement: A closeness story.

Since birth, infants discriminate the biological motion (BM) revealed by point-light displays (PLDs). To date, no studies have explored whether newborns differentiate BM that approaches rather than withdraws from them. Yet, approach and withdrawal are two fundamental motivations in the socio-emotional world, key to developing empathy and prosocial behavior. Through a looking-behavior paradigm, we demonstrated that a few hours after birth, a human figure approaching attracted more visual attention than a human figure receding, showing that newborns are attuned to PLDs of others moving toward rather than walking away from them. Further, a withdrawing body appears to be less attractive than withdrawing scrambled points. Altogether, these observations support the existence of an early predisposition toward social closeness that might have its roots in an evolutionary perspective.

Violent Offending in Males With or Without Schizophrenia: A Role for Social Cognition?

Reduced social cognition has been reported in individuals who have committed interpersonal violence. It is unclear if individuals with schizophrenia and a history of violence have larger impairments than violent individuals without psychosis and non-violent individuals with schizophrenia. We examined social cognition in two groups with violent offenses, comparing their performance to non-violent individuals with schizophrenia and healthy controls. Two social cognitive domains were assessed in four groups: men with a schizophrenia spectrum disorder with (SSD-V, n = 27) or without (SSD-NV, n = 42) a history of violence, incarcerated men serving preventive detention sentences (V, n = 22), and healthy male controls (HC, n = 76). Theory of mind (ToM) was measured with the Movie for the Assessment of Social Cognition (MASC), body emotion perception with Emotion in Biological Motion (EmoBio) test. Kruskal-Wallis H-tests revealed overall group differences for social cognition. SSD-V had a global and clinically significant social cognitive impairment. V had a specific impairment, for ToM. Binary logistic regressions predicting violence category membership from social cognition and psychosis (SSD status) were conducted. The model with best fit, explaining 18%-25% of the variance, had ToM as the only predictor. Social cognitive impairment was present in individuals with a history of violence, with larger and more widespread impairment seen in schizophrenia. ToM predicted violence category membership, psychosis did not. The results suggest a role for social cognition in understanding interpersonal violence.

Inhibitory TMS over Visual Area V5/MT Disrupts Visual Speech Recognition.

During face-to-face communication, the perception and recognition of facial movements can facilitate individuals' understanding of what is said. Facial movements are a form of complex biological motion. Separate neural pathways are thought to processing (1) simple, nonbiological motion with an obligatory waypoint in the motion-sensitive visual middle temporal area (V5/MT); and (2) complex biological motion. Here, we present findings that challenge this dichotomy. Neuronavigated offline transcranial magnetic stimulation (TMS) over V5/MT on 24 participants (17 females and 7 males) led to increased response times in the recognition of simple, nonbiological motion as well as visual speech recognition compared with TMS over the vertex, an active control region. TMS of area V5/MT also reduced practice effects on response times, that are typically observed in both visual speech and motion recognition tasks over time. Our findings provide the first indication that area V5/MT causally influences the recognition of visual speech.SIGNIFICANCE STATEMENT In everyday face-to-face communication, speech comprehension is often facilitated by viewing a speaker's facial movements. Several brain areas contribute to the recognition of visual speech. One area of interest is the motion-sensitive visual medial temporal area (V5/MT), which has been associated with the perception of simple, nonbiological motion such as moving dots, as well as more complex, biological motion such as visual speech. Here, we demonstrate using noninvasive brain stimulation that area V5/MT is causally relevant in recognizing visual speech. This finding provides new insights into the neural mechanisms that support the perception of human communication signals, which will help guide future research in typically developed individuals and populations with communication difficulties.

Prediction underlying comprehension of human motion: an analysis of Deaf signer and non-signer EEG in response to visual stimuli.

Sensory inference and top-down predictive processing, reflected in human neural activity, play a critical role in higher-order cognitive processes, such as language comprehension. However, the neurobiological bases of predictive processing in higher-order cognitive processes are not well-understood. This study used electroencephalography (EEG) to track participants' cortical dynamics in response to Austrian Sign Language and reversed sign language videos, measuring neural coherence to optical flow in the visual signal. We then used machine learning to assess entropy-based relevance of specific frequencies and regions of interest to brain state classification accuracy. EEG features highly relevant for classification were distributed across language processing-related regions in Deaf signers (frontal cortex and left hemisphere), while in non-signers such features were concentrated in visual and spatial processing regions. The results highlight functional significance of predictive processing time windows for sign language comprehension and biological motion processing, and the role of long-term experience (learning) in minimizing prediction error.

Moisture‐Insensitive Force Sensor Yarns and Fabrics to Monitor Biological Motion

AbstractTextile sensors are crucial unobtrusive devices attached to arbitrarily curved surfaces owing to their high flexibility and ease of processing in large areas with complex contours. However, issues regarding the reliability and stability of the output of textile sensors and their practical implementation persist. This study proposes sensor yarns comprising carbon‐coated multifibers covering metallic core yarns to detect pressure and strain. Two electrically independent metallic core fibers are twisted in close proximity in a core‐sheath structure with a sheath yarn of carbon‐coated fibers. When an external force is applied, the covering yarns deform elastically, causing a change in resistance. The proposed sensor yarns can be used to develop customized textile sensors, as they can be woven or knitted at the target positions owing to their flexibility. Fabrics and knits with embedded sensor yarns can detect external forces and biological motions, e.g., respiratory monitoring and finger movements. The proposed sensors can be made sensitive or insensitive to moisture depending on the choice of the covering yarn. Thus, the proposed yarns and textile sensors have potential applications in wearable devices and biological sensors that require high conformability to the human body and curved surfaces.

Understanding visual processing of motion: completing the picture using experimentally driven computational models of MT.

Computational modeling helps neuroscientists to integrate and explain experimental data obtained through neurophysiological and anatomical studies, thus providing a mechanism by which we can better understand and predict the principles of neural computation. Computational modeling of the neuronal pathways of the visual cortex has been successful in developing theories of biological motion processing. This review describes a range of computational models that have been inspired by neurophysiological experiments. Theories of local motion integration and pattern motion processing are presented, together with suggested neurophysiological experiments designed to test those hypotheses.

Sign language experience has little effect on face and biomotion perception in bimodal bilinguals

Sensory and language experience can affect brain organization and domain-general abilities. For example, D/deaf individuals show superior visual perception compared to hearing controls in several domains, including the perception of faces and peripheral motion. While these enhancements may result from sensory loss and subsequent neural plasticity, they may also reflect experience using a visual-manual language, like American Sign Language (ASL), where signers must process moving hand signs and facial cues simultaneously. In an effort to disentangle these concurrent sensory experiences, we examined how learning sign language influences visual abilities by comparing bimodal bilinguals (i.e., sign language users with typical hearing) and hearing non-signers. Bimodal bilinguals and hearing non-signers completed online psychophysical measures of face matching and biological motion discrimination. No significant group differences were observed across these two tasks, suggesting that sign language experience is insufficient to induce perceptual advantages in typical-hearing adults. However, ASL proficiency (but not years of experience or age of acquisition) was found to predict performance on the motion perception task among bimodal bilinguals. Overall, the results presented here highlight a need for more nuanced study of how linguistic environments, sensory experience, and cognitive functions impact broad perceptual processes and underlying neural correlates.

Constitutive formulations for intrinsic anisotropy in soft electroelastic materials

Inspired by biology and engineered soft active material systems, we propose a new constitutive formulation for a soft material consisting of soft contractile fibers embedded in a soft matrix. The mathematical implementation of the model is based on a multi-field invariant formulation within a nonlinear continuum mechanics framework. The coupled constitutive formulation highlights a new electromechanical coupling term that describes the intrinsic (or active) anisotropy due to the contractile units. The model demonstrates the relative role that intrinsic anisotropy plays in the overall stress response. The resulting formulation could be used to design and inspire the development of new soft material systems that seek to replicate three dimensional biological motion.

Visual sensitivity to biological motion invariants in humans at birth: Comment on "Motor invariants in action execution and perception" by Francesco Torricelli et al.

Visual sensitivity to biological motion invariants in humans at birth: Comment on "Motor invariants in action execution and perception" by Francesco Torricelli et al.

Life motion signals bias the perception of apparent motion direction.

Walking direction conveyed by biological motion (BM) cues, which humans are highly sensitive to since birth, can elicit involuntary shifts of attention to enhance the detection of static targets. Here, we demonstrated that such intrinsic sensitivity to walking direction could also modulate the direction perception of simultaneously presented dynamic stimuli. We showed that the perceived direction of apparent motion was biased towards the walking direction even though observers had been informed in advance that the walking direction of BM did not predict the apparent motion direction. In particular, rightward BM cues had an advantage over leftward BM cues in altering the perception of motion direction. Intriguingly, this perceptual bias disappeared when BM cues were shown inverted, or when the critical biological characteristics were removed from the cues. Critically, both the perceptual direction bias and the rightward advantage persisted even when only local BM cues were presented without any global configuration. Furthermore, the rightward advantage was found to be specific to social cues (i.e., BM), as it vanished when non-social cues (i.e., arrows) were utilized. Taken together, these findings support the existence of a specific processing mechanism for life motion signals and shed new light on their influences in a dynamic environment.