Communicative interactions in point-light displays: Choosing among multiple response alternatives

SmartDetector: Automatic and vision-based approach to point-light display generation for human action perception

Over the past four decades, point-light displays (PLD) have been integrated into psychology and psychophysics, providing a valuable means to probe human perceptual skills. Leveraging the inherent kinematic information and controllable display parameters, researchers have utilized this technique to examine the mechanisms involved in learning and rehabilitation. However, classical PLD generation methods (e.g., motion capture) are difficult to apply for behavior analysis in real-world situations, such as patient care or sports activities. Therefore, there is a demand for automated and affordable tools that enable efficient and real-world-compatible generation of PLDs for psychological research. In this paper, we propose SmartDetector, a new artificial intelligence (AI)-based tool for automatic PLD creation from RGB videos. To evaluate humans' perceptual skills for processing PLD building with SmartDetector, 126 participants were randomly assigned to recognition, discrimination, or detection tasks. Results demonstrated that, irrespective of the task, PLDs generated by SmartDetector exhibited commendable perceptual performance in terms of accuracy and response times compared to literature findings. Moreover, to enhance usability and broaden accessibility, we developed an intuitive web interface for our method, making it available to a wider audience. The resulting application is available at https://plavimop.prd.fr/index.php/en/automatic-creation-pld . SmartDetector offers interesting possibilities for using PLD in research and makes the use of PLD more accessible for nonacademic applications.

PLAViMoP database: A new continuously assessed and collaborative 3D point-light display dataset

It was more than 45 years ago that Gunnar Johansson invented the point-light display technique. This showed for the first time that kinematics is crucial for action recognition, and that humans are very sensitive to their conspecifics' movements. As a result, many of today's researchers use point-light displays to better understand the mechanisms behind this recognition ability. In this paper, we propose PLAViMoP, a new database of 3D point-light displays representing everyday human actions (global and fine-motor control movements), sports movements, facial expressions, interactions, and robotic movements. Access to the database is free, at https://plavimop.prd.fr/en/motions . Moreover, it incorporates a search engine to facilitate action retrieval. In this paper, we describe the construction, functioning, and assessment of the PLAViMoP database. Each sequence was analyzed according to four parameters: type of movement, movement label, sex of the actor, and age of the actor. We provide both the mean scores for each assessment of each point-light display, and the comparisons between the different categories of sequences. Our results are discussed in the light of the literature and the suitability of our stimuli for research and applications.

Two Means Together? Effects of Response Bias and Sensitivity on Communicative Action Detection

Numerous lines of research suggest that communicative dyadic actions elicit preferential processing and more accurate detection compared to similar but individual actions. However, it is unclear whether the presence of the second agent provides additional cues that allow for more accurate discriminability between communicative and individual intentions or whether it lowers the threshold for perceiving third-party encounters as interactive. We performed a series of studies comparing the recognition of communicative actions from single and dyadic displays in healthy individuals. A decreased response threshold for communicative actions was observed for dyadic vs. single-agent animations across all three studies, providing evidence for the dyadic communicative bias. Furthermore, consistent with the facilitated recognition hypothesis, congruent response to a communicative gesture increased the ability to accurately interpret the actions. In line with dual-process theory, we propose that both mechanisms may be perceived as complementary rather than competitive and affect different stages of stimuli processing.

Moving Toward versus Away from Another: How Body Motion Direction Changes the Representation of Bodies and Actions in the Visual Cortex

Representing multiple agents and their mutual relations is a prerequisite to understand social events such as interactions. Using functional magnetic resonance imaging on human adults, we show that visual areas dedicated to body form and body motion perception contribute to processing social events, by holding the representation of multiple moving bodies and encoding the spatial relations between them. In particular, seeing animations of human bodies facing and moving toward (vs. away from) each other increased neural activity in the body-selective cortex [extrastriate body area (EBA)] and posterior superior temporal sulcus (pSTS) for biological motion perception. In those areas, representation of body postures and movements, as well as of the overall scene, was more accurate for facing body (vs. nonfacing body) stimuli. Effective connectivity analysis with dynamic causal modeling revealed increased coupling between EBA and pSTS during perception of facing body stimuli. The perceptual enhancement of multiple-body scenes featuring cues of interaction (i.e., face-to-face positioning, spatial proximity, and approaching signals) was supported by the participants' better performance in a recognition task with facing body versus nonfacing body stimuli. Thus, visuospatial cues of interaction in multiple-person scenarios affect the perceptual representation of body and body motion and, by promoting functional integration, streamline the process from body perception to action representation.

Social Perception and Interaction Database-A Novel Tool to Study Social Cognitive Processes With Point-Light Displays

Introduction: The ability to detect and interpret social interactions (SI) is one of the crucial skills enabling people to operate in the social world. Multiple lines of evidence converge to indicate the preferential processing of SI when compared to the individual actions of multiple agents, even if the actions were visually degraded to minimalistic point-light displays (PLDs). Here, we present a novel PLD dataset (Social Perception and Interaction Database; SoPID) that may be used for studying multiple levels of social information processing. Methods: During a motion-capture session, two pairs of actors were asked to perform a wide range of 3-second actions, including: (1) neutral, gesture-based communicative interactions (COM); (2) emotional exchanges (Happy/Angry); (3) synchronous interactive physical activity of actors (SYNC); and (4) independent actions of agents, either object-related (ORA) or non-object related (NORA). An interface that allows single/dyadic PLD stimuli to be presented from either the second person (action aimed toward the viewer) or third person (observation of actions presented toward other agents) perspective was implemented on the basis on the recorded actions. Two validation studies (each with 20 healthy individuals) were then performed to establish the recognizability of the SoPID vignettes. Results: The first study showed a ceiling level accuracy for discrimination of communicative vs. individual actions (93% ± 5%) and high accuracy for interpreting specific types of actions (85 ± 4%) from the SoPID. In the second study, a robust effect of scrambling on the recognizability of SoPID stimuli was observed in an independent sample of healthy individuals. Discussion: These results suggest that the SoPID may be effectively used to examine processes associated with communicative interactions and intentions processing. The database can be accessed via the Open Science Framework (https://osf.io/dcht8/).

The Emerging Science of People-Watching: Forming Impressions From Third-Party Encounters

Traditional impression formation studies have focused almost exclusively on the perception and evaluation of isolated individuals. In recent years, however, portrayals of third-party encounters between two (or more) people have been used increasingly often to probe impressions about the interactions and relations between individuals. This tacit paradigm change has revealed an intriguing scope of judgments that concern how and why people relate to one another. Though these judgments recruit well-known neural networks of impression formation, their underlying cognitive operations and functional significance remain largely speculative. By providing an overview of recent theoretical and empirical approaches on encounter-based impressions, this article highlights their prevalent role in human social cognition.

The Multilingual CID-5: A New Tool to Study the Perception of Communicative Interactions in Different Languages

The investigation of the ability to perceive, recognize, and judge upon social intentions, such as communicative intentions, on the basis of body motion is a growing research area. Cross-cultural differences in ability to perceive and interpret biological motion, however, have been poorly investigated so far. Progress in this domain strongly depends on the availability of suitable stimulus material. In the present method paper, we describe the multilingual CID-5, an extension of the CID-5 database, allowing for the investigation of how non-conventional communicative gestures are classified and identified by speakers of different languages. The CID-5 database contains 14 communicative interactions and 7 non-communicative actions performed by couples of agents and presented as point-light displays. For each action, the database provides movie files with the point-light animation, text files with the 3-D spatial coordinates of the point-lights, and five different response alternatives. In the multilingual CID-5 the alternatives were translated into seven languages (Chinese, Dutch, English, French, German, Italian, and Polish). Preliminary data collected to assess the recognizability of the actions in the different languages suggest that, for most of the action stimuli, information presented in point-light displays is sufficient for the distinctive classification of the action as communicative vs. individual, as well as for identification of the specific communicative gesture performed by the actor in all the available languages.