Biological Motion Research Articles

The discrimination of expressions in facial movements by infants: A study with point-light displays

Perceiving facial expressions is an essential ability for infants. Although previous studies indicated that infants could perceive emotion from expressive facial movements, the developmental change of this ability remains largely unknown. To exclusively examine infants’ processing of facial movements, we used point-light displays (PLDs) to present emotionally expressive facial movements. Specifically, we used a habituation and visual paired comparison (VPC) paradigm to investigate whether 3-, 6-, and 9-month-olds could discriminate between happy and fear PLDs after being habituated with a happy PLD (happy-habituation condition) or a fear PLD (fear-habituation condition). The 3-month-olds discriminated between the happy and fear PLDs in both the happy- and fear-habituation conditions. The 6- and 9-month-olds showed discrimination only in the happy-habituation condition but not in the fear-habituation condition. These results indicated a developmental change in processing expressive facial movements. Younger infants tended to process low-level motion signals regardless of the depicted emotions, and older infants tended to process expressions, which emerged in familiar facial expressions (e.g., happy). Additional analyses of individual difference and eye movement patterns supported this conclusion. In Experiment 2, we concluded that the findings of Experiment 1 were not due to a spontaneous preference for fear PLDs. Using inverted PLDs, Experiment 3 further suggested that 3-month-olds have already perceived PLDs as face-like stimuli.

Alternative brain connectivity underscores age-related differences in the processing of interactive biological motion.

Rapidly recognizing and understanding others' social interactions is an important ability that relies on deciphering multiple sources of information; for example, perceiving body information and inferring others' intentions. Despite recent advances in characterizing the brain basis of this ability in adults, its developmental underpinnings are virtually unknown. Here, we used fMRI to investigate which sources of social information support superior temporal sulcus (STS) responses to interactive biological motion (i.e. 2 interacting point-light human figures) at different developmental intervals in human participants (of either sex): Children show supportive functional connectivity with key nodes of the mentalizing network, while adults show stronger reliance on regions associated with body- and dynamic social interaction/biological motion processing. We suggest that adults employ efficient action-intention understanding via body and biological motion information, while children show a stronger reliance on hidden mental-state inferences as a potential means of learning to better understand others' interactive behavior.SIGNIFICANCE STATEMENT:Recognizing others' interactive behavior is a critical human skill that depends on different sources of social information (e.g. observable body-action information, inferring others' hidden mental-states etc.). Understanding the brain-basis of this ability, and characterizing how it emerges across development are important goals in social neuroscience. Here, we used fMRI to investigate which sources of social information support interactive biological motion processing in children (6-12 years) and adults. These results reveal a striking developmental difference in terms of how wider-brain connectivity shapes functional responses to interactive biological motion that suggests a reliance on distinct neuro-cognitive strategies in service of interaction understanding (i.e. children and adults show a greater reliance on explicit and implicit intentional inference, respectively).

Ultrastretchable, Multihealable, and Highly Sensitive Strain Sensor Based on a Double Cross-Linked MXene Hydrogel

The ability of a flexible strain sensor to directly adapt the complicated human biological motion or combined gestures and remotely control the artificial intelligence robotics could benefit the wearable electronics such as intelligent robotics and patient healthcare. However, it is a challenge for the flexible strain sensor to simultaneously achieve high sensing performances and stretchability and long sustainability under various deformation stress or damage. Herein, a dual-cross-linked poly(acrylic acid-stearyl methacrylate)/MXene [P(AA-SMA)M] hydrogel with enhanced mechanical stretchability and self-healability is fabricated by importing reversible coordination and hydrophobic interaction into polymer networks. As a result, the hydrogel film not only exhibits high tensile strength (525 kPa) and stretchability (∼2600%) but also achieves repetitive healable property with 843% elongation even after the 20th broken/self-healing cycle. More importantly, the resultant strain sensor delivers a low detection limit, wide sensing range, fast response time, and repeatability of 1000 cycles even after repeated self-healing. So, the sensor can monitor subtle human motions and recognize different handwriting and gestures, which reveals potential applications toward health-care devices, flexible electronics, and human-machine interfacing.

The Role of Objecthood and Animacy in Apparent Movement Processing.

Although the ability to detect the actions of other living beings is key for adaptive social behavior, it is still unclear if biological motion perception is specific to human stimuli. Biological motion perception involves both bottom-up processing of movement kinematics ('motion pathway) and top-down reconstruction of movement from changes in body posture ('form pathway'). Previous research using point-light displays has shown that processing in the motion pathway depends on the presence of a well-defined, recognizable shape (objecthood) but not necessarily on whether that shape depicts a living being (animacy). Here, we focused on the form pathway. Specifically, we combined EEG frequency tagging with apparent motion to study how objecthood and animacy influence posture processing and the integration of postures into movements. By measuring brain responses to repeating sequences of well-defined or pixelated images (objecthood), depicting human or corkscrew agents (animacy), performing either fluent or non-fluent movements (movement fluency), we found that movement processing was sensitive to objecthood but not animacy. In contrast, posture processing was sensitive to both. Together, these results indicate that reconstructing biological movement from apparent motion sequences requires a well-defined, but not necessarily an animate shape. Instead, stimulus animacy appears to be relevant only for posture processing.

Making night-time pedestrians safer using innovative clothing designs

Night-time pedestrians, including recreational walkers and runners, remain at significant risk of being killed or seriously injured, because drivers often fail to see them in time to avoid a collision. Clothing incorporating retro-reflective markers on the moveable joints creates a visual perception of biological motion or “biomotion” which has been shown to improve night-time pedestrian conspicuity. This study investigated whether clothing with markings in the biomotion configuration retains its conspicuity if adapted to include thinner or patterned retro-reflective strips making it more acceptable to wear for recreational pedestrians. In a night-time closed road study, the relative conspicuity of pedestrians to 14 young drivers with normal vision (mean age 24.3 ± 3.1 years) was assessed for pedestrians wearing different thicknesses and patterns of biomotion strips and compared with typical clothing worn by night-time pedestrians, including commercially available sports clothing with retro-reflective elements, a fluorescent yellow top, and black clothing. Results showed that all the biomotion configurations resulted in significantly longer recognition distances: around 2 times longer than the sports clothing, 2.5 times longer than the fluorescent top and 4 times longer than the black clothing. Similar trends were found for the distance at which drivers correctly identified pedestrian orientation (towards or sideways to the vehicle), with significantly longer distances for all the biomotion configurations, when compared to the sports, fluorescent top and black clothing. These findings highlight the effectiveness of biomotion clothing, even when using retro-reflective strips as thin as 0.75 cm and have implications for clothing designs for recreational walkers and runners to enhance their night-time safety.

Stability Control of Quadruped Robot Based on Active State Adjustment.

The quadruped robot has a strong motion performance and broad application prospects in practical applications. However, during the movement of the quadruped robot, it is easy to be affected by external disturbance and environmental changes, which makes it unable to achieve the ideal effect movement. Therefore, it is very important for the quadruped robot to adjust actively according to its own state detection. This paper proposes an active state adjustment control method based on its own state, which can realize disturbance recovery and active environment adaptation. Firstly, the controller is designed according to the physical model of the quadruped robot, and the foot forces are optimized using the quadratic program (QP) method. Then, the disturbance compensation method based on dynamic analysis is studied and combined with the controller itself. At the same time, according to the law of biological movement, the movement process of the quadruped robot is actively adjusted according to the different movement environment, so that it can adapt to various complex environments. Finally, it is verified in a simulation environment and quadruped robot prototype. The results show that the quadruped robot has a strong active disturbance recovery ability and active environment adaptability.

Using Biological Motion to Investigate Perceptual-Cognitive Expertise in Law Enforcement Use-of-Force Decisions.

Research focused on police officers' decision-making in ambiguous use-of-force situations has yet to investigate the role that a suspect's biological motion plays in unknown-object identification. The current study uses point-light displays to isolate the suspect's motion and remove potentially biasing information (e.g., skin tone, facial expression, clothing). Experienced law enforcement officers and trainees (n = 129) watched point-light display videos of an actor pulling either a weapon or a non-weapon from a concealed location in a threatening or non-threatening manner. After each video ended, participants indicated whether the object-which was not visible-was a weapon or a non-weapon. Results indicated that the speed and intent (e.g., threatening vs. non-threatening) with which the actor drew the object were significant predictors of officers' responses. Officers' law enforcement experience (i.e., years of service) was not a significant predictor of their response. This study has important implications for understanding why police sometimes make critical and costly errors in ambiguous use-of-force situations. We consider implications for police performance and developing improved training procedures.

A Bayesian Network Approach to Social and Nonsocial Cognition in Schizophrenia: Are Some Domains More Fundamental than Others?

Social and nonsocial cognition are defined as distinct yet related constructs. However, the relative independence of individual variables-and whether specific tasks directly depend on performance in other tasks-is still unclear. The current study aimed to answer this question by using a Bayesian network approach to explore directional dependencies among social and nonsocial cognitive domains. The study sample comprised 173 participants with schizophrenia (71.7% male; 28.3% female). Participants completed 5 social cognitive tasks and the MATRICS Consensus Cognitive Battery. We estimated Bayesian networks using directed acyclic graph structures to examine directional dependencies among the variables. After accounting for negative symptoms and demographic variables, including age and sex, all nonsocial cognitive variables depended on processing speed. More specifically, attention, verbal memory, and reasoning and problem solving solely depended on processing speed, while a causal chain emerged between processing speed and visual memory (processing speed → attention → working memory → visual memory). Social processing variables within social cognition, including emotion in biological motion and empathic accuracy, depended on facial affect identification. These results suggest that processing speed and facial affect identification are fundamental domains of nonsocial and social cognition, respectively. We outline how these findings could potentially help guide specific interventions that aim to improve social and nonsocial cognition in people with schizophrenia.

Recognition of humans from biological motion in infants.

Infant studies have suggested that the detection of biological motion (BM) might be an innate capacity, based on newborns' spontaneous preference for BM. However, it is unclear if, like adults, infants recognize humans from BM and are able to build the representation of bodies and faces. To address this issue, we tested whether exposure to BM influences subsequent face recognition in 3- to 8-month-old infants. After familiarization with a point-light walker (PLW) of either a female or a male, the infant's preference for female and male faces was measured. If infants can build the representation of not only the body but also the face from PLWs, the familiarization effect of gender induced by the PLW might be generalized to faces. We found that infants at 7 to 8 months looked for longer at the face whose gender was opposite to that of the PLW, whereas 3- to 4- and 5- to 6-month-old infants did not. These results suggest that infants can access the representation of humans from BM and extract gender, which is shared across bodies and faces, from at least 7 to 8 months of age.

Motor invariants in action execution and perception.

The nervous system is sensitive to statistical regularities of the external world and forms internal models of these regularities to predict environmental dynamics. Given the inherently social nature of human behavior, being capable of building reliable predictive models of others' actions may be essential for successful interaction. While social prediction might seem to be a daunting task, the study of human motor control has accumulated ample evidence that our movements follow a series of kinematic invariants, which can be used by observers to reduce their uncertainty during social exchanges. Here, we provide an overview of the most salient regularities that shape biological motion, examine the role of these invariants in recognizing others' actions, and speculate that anchoring socially-relevant perceptual decisions to such kinematic invariants provides a key computational advantage for inferring conspecifics' goals and intentions.

Neural responses to biological motion distinguish autistic and schizotypal traits.

Difficulties in social interactions characterize both autism and schizophrenia and are correlated in the neurotypical population. It is unknown whether this represents a shared etiology or superficial phenotypic overlap. Both conditions exhibit atypical neural activity in response to the perception of social stimuli and decreased neural synchronization between individuals. This study investigated if neural activity and neural synchronization associated with biological motion perception are differentially associated with autistic and schizotypal traits in the neurotypical population. Participants viewed naturalistic social interactions while hemodynamic brain activity was measured with fMRI, which was modeled against a continuous measure of the extent of biological motion. General linear model analysis revealed that biological motion perception was associated with neural activity across the action observation network. However, intersubject phase synchronization analysis revealed neural activity to be synchronized between individuals in occipital and parietal areas but desynchronized in temporal and frontal regions. Autistic traits were associated with decreased neural activity (precuneus and middle cingulate gyrus), and schizotypal traits were associated with decreased neural synchronization (middle and inferior frontal gyri). Biological motion perception elicits divergent patterns of neural activity and synchronization, which dissociate autistic and schizotypal traits in the general population, suggesting that they originate from different neural mechanisms.

Figure-Ground Segmentation and Biological Motion Perception in Peripheral Visual Field.

Biological motion perception is a specific type of perceptual organization, during which a clear image of a moving human body is perceptually generated in virtue of certain core light dots representing the major joint movements. While the processes of biological motion perception have been studied extensively for almost a century, there is still a debate on whether biological motion task performance can be equally precise across all visual field or is central visual field specified for biological motion perception. The current study explores the processes of biological motion perception and figure-ground segmentation in the central and peripheral visual field, expanding the understanding of perceptual organization across different eccentricities. The method involved three different tasks of visual grouping: (1) a static visual grouping task, (2) a dynamic visual grouping task, and (3) a biological motion detection task. The stimuli in (1) and (2) were generated from 12-13 dots grouped by proximity and common fate, and, in (3), light dots representing human motion. All stimuli were embedded in static or dynamics visual noise and the threshold value for the number of noise dots in which the elements could still be grouped by proximity and/or common fate was determined. The results demonstrate that biological motion can be differentiated from the scrambled set of moving dots in a more intensive visual noise than static and dynamic visual grouping tasks. Furthermore, in all three visual tasks (static and dynamic grouping, and biological motion detection) the performance was significantly worse in the periphery than in the central visual field, and object magnification could not compensate for the reduced performance in any of the three grouping tasks. The preliminary results of nine participants indicate that (a) human motion perception involves specific perceptual processes, providing the high-accuracy perception of the human body and (b) the processes of figure-ground segmentation are governed by the bottom-up processes and the best performance can be achieved only when the object is demonstrated in the central visual field.

Applications of Triboelectric Nanogenerators in Bone Tissue Engineering

AbstractBioelectricity has been a fundamental property of all living organisms. With electrical stimulation, living cells can interact with their microenvironments, which makes electrical stimulation highly beneficial for various biomedical applications. However, traditional electrical stimulation mainly relies on bulky and complex equipment, which may not be ideal due to the restriction of movement, limited battery lifetime, uncomfortable wearing, and potential unfriendly to the environment. The advent of triboelectric nanogenerators (TENGs) has helped to resolve the existing limitations. TENGs are effective energy harvesting systems that use a mix of triboelectrification and electrostatic induction to create electrical energy from kinetic energy. TENGs deliver self‐powered electrical stimulation to bone cells for functional regulation or bone regeneration, serve as sensors to detect biological signals or movements, or act as a power source for other biomedical devices. TENGs can be employed in various applications, including enhancing bone regeneration, providing sensing function, slowing bone aging, and curing implant‐related infections. The recent applications of TENGs in bone tissue engineering are reviewed, and the drawbacks of the TENGs are discussed. Finally, the existing challenges and future roadmap for developing TENGs are presented.

Encoding of dynamic facial information in the middle dorsal face area

Faces in motion reveal a plethora of information through visual dynamics. Faces can move in complex patterns while transforming facial shape, e.g., during the generation of different emotional expressions. While motion and shape processing have been studied extensively in separate research enterprises, much less is known about their conjunction during biological motion. Here, we took advantage of the discovery in brain-imaging studies of an area in the dorsal portion of the macaque monkey superior temporal sulcus (STS), the middle dorsal face area (MD), with selectivity for naturalistic face motion. To gain mechanistic insights into the coding of facial motion, we recorded single-unit activity from MD, testing whether and how MD cells encode face motion. The MD population was highly sensitive to naturalistic facial motion and facial shape. Some MD cells responded only to the conjunction of facial shape and motion, others were selective for facial shape even without movement, and yet others were suppressed by facial motion. We found that this heterogeneous MD population transforms face motion into a higher dimensional activity space, a representation that would allow for high sensitivity to relevant small-scale movements. Indeed, we show that many MD cells carry such sensitivity for eye movements. We further found that MD cells encode motion of head, mouth, and eyes in a separable manner, requiring the use of multiple reference frames. Thus, MD is a bona fide face-motion area that uses highly heterogeneous cell populations to create codes capturing even complex facial motion trajectories.

Low-cost real-time VLSI system for high-accuracy optical flow estimation using biological motion features and random forests

Low-cost real-time VLSI system for high-accuracy optical flow estimation using biological motion features and random forests

Ribosome hyper-swivel head domain motions are required for translocation and resetting.

Translocation of messenger RNA (mRNA) and transfer RNA (tRNA) substrates through the ribosome during protein synthesis, an exemplar of directional molecular movement in biology, entails a complex interplay of conformational, compositional, and chemical changes. The molecular determinants of early translocation steps have been investigated rigorously. However, the elements enabling the ribosome to complete translocation and reset for subsequent protein synthesis reactions remain poorly understood. Here, we have combined molecular simulations with single-molecule fluorescence resonance energy transfer imaging to gain insights into the rate-limiting events of the translocation mechanism.1 We find that diffusive motions of the ribosomal small subunit head domain to hyper-swivelled positions, governed by universally conserved rRNA, can maneuver the mRNA and tRNAs to their fully translocated positions. Subsequent engagement of peptidyl-tRNA and disengagement of deacyl-tRNA from mRNA, within their respective small subunit binding sites, facilitate the ribosome resetting mechanism after translocation has occurred to enable protein synthesis to resume.1Nishima, et al., Nucleic Acids Research, Volume 50, 8302-8320, 2022.

A spontaneous gravity prior: newborn chicks prefer stimuli that move against gravity.

At the beginning of life, inexperienced animals use evolutionary-given preferences (predispositions) to decide what stimuli to attend and approach. Stimuli that contain cues of animacy, such as face-like stimuli, biological motion and changes in speed, are particularly attractive across vertebrate taxa. A strong cue of animacy is upward movement against terrestrial gravity, because only animate objects consistently move upward. To test whether upward movement is spontaneously considered attractive already at birth, we tested the early preferences of dark-hatched chicks (Gallus gallus) for upward- versus downward-moving visual stimuli. We found that, without any previous visual experience, chicks consistently exhibited a preference to approach stimuli that move upward, against gravity. A control experiment showed that these preferences are not driven by avoidance of downward stimuli. These results show that newborn animals have a gravity prior that attracts them toward upward movement. Movement against gravity can be used as a cue of animacy to orient early approach responses in the absence of previous visual experience.

Life Detection From Biological Motion

Life motion, the active movements of people and other animals, contains a wealth of information that is potentially accessible to the visual system of an observer. Biological-motion point-light displays have been widely used to study both the information contained in life motion stimuli and the visual mechanisms that make use of it. Biological motion conveys motion-mediated dynamic shape, which in turn can be used for identification and recognition of the agent, but it also contains local visual invariants that humans and other animals use as a general detection system that signals the presence of other agents in the visual environment. Here, we review recent research on behavioral, neurophysiological, and genetic aspects of this life-detection system and discuss its functional significance in the light of earlier hypotheses.

Bionic Shape Memory Polyurethane/Prussian Blue Nanoparticle-Based Actuators with Two-Way and Programmable Light-Driven Motions

A bionic smart actuator that can imitate types of biological motions plays a vital role in intelligent systems, which therefore becomes one of the hottest development directions in recent years and has attracted more and more attention from researchers. In this study, a kind of near-infrared (NIR) light-responsive shape memory polyurethane SMPU-PB is developed by doping the citric acid-modified Prussian blue nanoparticles. Based on it, a bionic “athlete” has performed repeatable photomechanical jumping behavior to cross obstacles under 808 nm NIR light irradiation. Furthermore, through the integration of SMPU-PB with pre-strained UV-responsive polyurethane film, a hybrid wavelength-selective responsive structure capable of reversible, programmable, and controllable motions is produced. By using the two-way light-driven shape memory composite, the bionic actuator is able to complete a series of tasks including accurate bending and mechanical gripping.

Reading the mind in the eyes of Black and White people: Interracial contact and perceived race affects brain activity when inferring mental states

Inferring others’ mental states, or mentalizing, is a critical social cognitive ability that underlies humans’ remarkable capacity for complex social interactions. Recent work suggests that interracial contact shapes the recruitment of brain regions involved in mentalizing during impression formation. However, it remains unclear how a target's perceived racial group and a perceiver's previous contact with that racial group shapes mental state inferences. In this study, we examined brain activity in regions of interest associated with mentalizing and race perception among self-identified White perceivers who varied in lifetime contact while they inferred secondary emotions from perceived White eyes and perceived Black eyes (i.e., the Reading the Mind in the Eyes test). The interaction between lifetime contact and perceived target race predicted activity in the superior temporal sulcus (STS), a region consistently implicated in mental state inferences from perceptual cues, tracking eye gaze, and biological motion. Low and average contact White perceivers showed more left STS activity when inferring mental states from perceived White eyes than perceived Black eyes, whereas high contact White perceivers showed similar left STS activity regardless of perceived target race. These results indicate that interracial contact decreases racial biases in the recruitment of regions involved in mentalizing when inferring mental states from perceptual cues.