TAT-HUM: Trajectory analysis toolkit for human movements in Python.

Human movement trajectories can reveal useful insights regarding the underlying mechanisms of human behaviors. Extracting information from movement trajectories, however, can be challenging because of their complex and dynamic nature. The current paper presents a Python toolkit developed to help users analyze and extract meaningful information from the trajectories of discrete rapid aiming movements executed by humans. This toolkit uses various open-source Python libraries, such as NumPy and SciPy, and offers a collection of common functionalities to analyze movement trajectory data. To ensure flexibility and ease of use, the toolkit offers two approaches: an automated approach that processes raw data and generates relevant measures automatically, and a manual approach that allows users to selectively use different functions based on their specific needs. A behavioral experiment based on the spatial cueing paradigm was conducted to illustrate how one can use this toolkit in practice. Readers are encouraged to access the publicly available data and relevant analysis scripts as an opportunity to learn about kinematic analysis for human movements.

Explicit effort may not influence perceptuomotor decision-making.

Many decisions that humans make are enacted by the action system. For example, humans use reach-to-grasp movements when making perceptuomotor decisions between and obtaining fruits of varying quality from a pile. Recent work suggests that the characteristics of each action alternative may influence the decision itself-there may be a bias away from making perceptuomotor alternatives associated with high effort when participants are unaware of the effort differences between responses. The present study examined if perceptuomotor decisions were influenced by explicit reaching effort differences. Neurotypical human participants were presented with random dot motion stimuli in which most dots moved in random directions and varying percentages of remaining dots moved coherently left- or rightward. Participants reported leftward motion judgements by performing leftward (or left hand) reaching movements and rightward motion judgements by performing rightward (or right hand) reaching movements. A resistance band was affixed to participants' wrists and to the table in different configurations. The configurations allowed for one movement/motion direction judgement to always require stretching of the band and, therefore, require relatively more effort. Across a set of experiments, the response context (i.e. selecting directions within a limb or selecting between limbs) and the effort difference between responses were manipulated. Overall, no experiment revealed a bias away from the perceptuomotor decision associated with high effort. Based on these results, it is concluded that, in this biomechanical context, explicit effort may not influence perceptuomotor decision-making and may point to a contextual influence of action effort on perceptuomotor decision-making.

What we imagine learning from watching others: how motor imagery modulates competency perceptions resulting from the repeated observation of a juggling action.

Although motor learning can occur from observing others perform a motor skill (action observation; AO), observers' confidence in their own ability to perform the skill can be falsely increased compared to their actual ability. This illusion of motor competence (i.e., 'over-confidence') may arise because the learner does not gain access to sensory feedback about their own performance-a source of information that can help individuals understand their veridical motor capabilities. Unlike AO, motor imagery (MI; the mental rehearsal of a motor skill) is thought to be linked to an understanding of movement consequences and kinaesthetic information. MI may thus provide the learner with movement-related diagnostic information, leading to greater accuracy in assessing ability. The present study was designed to evaluate the effects of MI when paired with AO in assessments of one's own motor capabilities in an online observation task. Two groups rated their confidence in performing a juggling task following repeated observations of the action without MI (OBS group; n = 45) or with MI following observation (OBS+MI; n = 39). As predicted, confidence increased with repeated observation for both groups, yet increased to a greater extent in the OBS relative to the OBS+MI group. The addition of MI appeared to reduce confidence that resulted from repeated AO alone. Data support the hypothesis that AO and MI are separable and that MI allows better access to sensory information than AO. However, further research is required to assess changes in confidence that result from MI alone and motor execution.

Increased preparation time reduces, but does not abolish, action history bias of saccadic eye movements.

The characteristics of movements are strongly history-dependent. Marinovic et al. (Marinovic W, Poh E, de Rugy A, Carroll TJ. eLife 6: e26713, 2017) showed that past experience influences the execution of limb movements through a combination of temporally stable processes that are strictly use dependent and dynamically evolving and context-dependent processes that reflect prediction of future actions. Here we tested the basis of history-dependent biases for multiple spatiotemporal features of saccadic eye movements under two preparation time conditions (long and short). Twenty people performed saccades to visual targets. To prompt context-specific expectations of most likely target locations, 1 of 12 potential target locations was specified on ~85% of the trials and each remaining target was presented on ~1% trials. In long preparation trials participants were shown the location of the next target 1 s before its presentation onset, whereas in short preparation trials each target was first specified as the cue to move. Saccade reaction times and direction were biased by recent saccade history but according to distinct spatial tuning profiles. Biases were purely expectation related for saccadic reaction times, which increased linearly as the distance from the repeated target location increased when preparation time was short but were similar to all targets when preparation time was long. By contrast, the directions of saccades were biased toward the repeated target in both preparation time conditions, although to a lesser extent when the target location was precued (long preparation). The results suggest that saccade history affects saccade dynamics via both use- and expectation-dependent mechanisms and that movement history has dissociable effects on reaction time and saccadic direction. NEW & NOTEWORTHY The characteristics of our movements are influenced not only by concurrent sensory inputs but also by how we have moved in the past. For limb movements, history effects involve both use-dependent processes due strictly to movement repetition and processes that reflect prediction of future actions. Here we show that saccade history also affects saccade dynamics via use- and expectation-dependent mechanisms but that movement history has dissociable effects on saccade reaction time and direction.

It is not in the details: Self-related shapes are rapidly classified but their features are not better remembered.

Self-prioritization is a robust phenomenon whereby judgments concerning self-representational stimuli are faster than judgments toward other stimuli. The present paper examines if and how self-prioritization causes more vivid short-term memories for self-related objects by giving geometric shapes arbitrary identities (self, mother, stranger). In Experiment 1 participants were presented with an array of the three shapes and required to retain the location and color of each in memory. Participants were then probed regarding the identity of one of the shapes and subsequently asked to indicate the color of the probed shape or an unprobed shape on a color wheel. Results indicated no benefit for self-stimuli in either response time for the identification probe or for color fidelity in memory. Yet, a cuing benefit was observed such that the cued stimulus in the identity probe did have higher fidelity within memory. Experiments 2 and 3 reduced the cognitive load by only requiring that participants process the identity and color of one shape at a time. For Experiment 2, the identity probe was memory-based, whereas the stimulus was presented alongside the identity probe for Experiment 3. Results demonstrated a robust self-prioritization effect: self-related shapes were classified faster than non-self-shapes, but this self-advantage did not lead to an increase in the fidelity of memory for self-related shapes' colors. Overall, these results suggest that self-prioritization effects may be restricted to an improvement in the ability to recognize that the self-representational stimulus is present without devoting more perceptual and short-term memory resources to such stimuli.

An optimal velocity for online limb-target regulation processes?

The utilization of visual information for the control of ongoing voluntary limb movements has been investigated for more than a century. Recently, online sensorimotor processes for the control of upper-limb reaches were hypothesized to include a distinct process related to the comparison of limb and target positions (i.e., limb-target regulation processes: Elliott et al. in Psychol Bull 136:1023-1044. doi: 10.1037/a0020958 , 2010). In the current study, this hypothesis was tested by presenting participants with brief windows of vision (20 ms) when the real-time velocity of the reaching limb rose above selected velocity criteria. One experiment tested the perceptual judgments of endpoint bias (i.e., under- vs. over-shoot), and another experiment tested the shifts in endpoint distributions following an imperceptible target jump. Both experiments revealed that limb-target regulation processes take place at an optimal velocity or "sweet spot" between movement onset and peak limb velocity (i.e., 1.0 m/s with the employed movement amplitude and duration). In contrast with pseudo-continuous models of online control (e.g., Elliott et al. in Hum Mov Sci 10:393-418. doi: 10.1016/0167-9457(91)90013-N , 1991), humans likely optimize online limb-target regulation processes by gathering visual information at a rather limited period of time, well in advance of peak limb velocity.

Response-specific effects in a joint action task: social inhibition of return effects do not emerge when observed and executed actions are different.

Although the inhibition of return (IOR) effect is primarily studied when people act individually, IOR is also observed in social environments where a person observes a partner's response before executing their own response (social or sIOR). Specifically, an observer takes longer to initiate a response to a target at a location that another individual has just responded to than to another location. The present study was conducted to determine if sIOR emerges when two individuals execute different actions-one participant executed keypress responses and the other completed aiming movements to the same set of stimuli. The two conditions in the present experiment were designed to separate the effects of observing a co-actor's target information from observing their subsequent response. In the Full Vision condition, observers saw both the target stimuli and the response of the partner. In the Partial Vision condition, observers witnessed the response of the partner, but did not see the target stimulus or any other potentially attention capturing event at the target location. It was found that, although sIOR emerged in the Full Vision condition, sIOR did not emerge in the Partial Vision condition. These and other previous findings on the impact of action goal on sIOR are discussed with reference to the potential contributions of attention and action co-representation mechanisms to the sIOR effect.

Ownership Status Influences the Degree of Joint Facilitatory Behavior.

When engaging in joint activities, humans tend to sacrifice some of their own sensorimotor comfort and efficiency to facilitate a partner's performance. In the two experiments reported here, we investigated whether ownership-a socioculturally based nonphysical feature ascribed to objects-influenced facilitatory motor behavior in joint action. Participants passed mugs that differed in ownership status across a table to a partner. We found that participants oriented handles less toward their partners when passing their own mugs than when passing mugs owned by their partners (Experiment 1) and mugs owned by the experimenter (Experiment 2). These findings indicate that individuals plan and execute actions that assist their partners but do so to a smaller degree if it is the individuals' own property that the partners intend to manipulate. We discuss these findings in terms of underlying variables associated with ownership and conclude that a self-other distinction can be found in the human sensorimotor system.

The violation of Fitts' Law: an examination of displacement biases and corrective submovements.

Fitts' Law holds that, to maintain accuracy, movement times of aiming movements must change as a result of varying degrees of movement difficulty. Recent evidence has emerged that aiming to a target located last in an array of placeholders results in a shorter movement time than would be expected by the Fitts' equation-a violation of Fitts' Law. It has been suggested that the violation emerges because the performer adopts an optimized movement strategy in which they partially pre-plan an action to the closest placeholder (undershoot the last placeholder) and rely on a secondary acceleration to propel the limb toward the last location when it is selected as the target (Glazebrook et al. in Hum Mov Sci 39:163-176, 2015). In the current study, we examine this proposal and further elucidate the processes underlying the violation by examining limb displacement and corrective submovements that occur when performers aim to different target locations. For our Main Study, participants executed discrete aiming movements in a five-placeholder array. We also reanalyzed data from a previously reported study in which participants aimed in placeholder and no-placeholder conditions (Blinch et al. in Exp Brain Res 223:505-515, 2012). The results showed the violation of Fitts' Law unfolded following peak velocity (online control). Further, the analysis showed that movements to the last target tended to overshoot and had a higher proportion of secondary submovements featuring a reversal than other categories of submovement (secondary accelerations, discontinuities). These findings indicate that the violation of Fitts' Law may, in fact, result from a strategic bias toward planning farther initial displacements of the limb which accommodates a shorter time in online control.

The processing of visual and auditory information for reaching movements.

Presenting target and non-target information in different modalities influences target localization if the non-target is within the spatiotemporal limits of perceptual integration. When using auditory and visual stimuli, the influence of a visual non-target on auditory target localization is greater than the reverse. It is not known, however, whether or how such perceptual effects extend to goal-directed behaviours. To gain insight into how audio-visual stimuli are integrated for motor tasks, the kinematics of reaching movements towards visual or auditory targets with or without a non-target in the other modality were examined. When present, the simultaneously presented non-target could be spatially coincident, to the left, or to the right of the target. Results revealed that auditory non-targets did not influence reaching trajectories towards a visual target, whereas visual non-targets influenced trajectories towards an auditory target. Interestingly, the biases induced by visual non-targets were present early in the trajectory and persisted until movement end. Subsequent experimentation indicated that the magnitude of the biases was equivalent whether participants performed a perceptual or motor task, whereas variability was greater for the motor versus the perceptual tasks. We propose that visually induced trajectory biases were driven by the perceived mislocation of the auditory target, which in turn affected both the movement plan and subsequent control of the movement. Such findings provide further evidence of the dominant role visual information processing plays in encoding spatial locations as well as planning and executing reaching action, even when reaching towards auditory targets.

Hand position influences perceptual grouping.

Over the past decade, evidence has accumulated that performance in attention, perception, and memory-related tasks are influenced by the distance between the hands and the stimuli (i.e., placing the observer's hands near or far from the stimuli). To account for existing findings, it has recently been proposed that processing of stimuli near the hands is dominated by the magnocellular visual pathway. The present study tests an implication of this hypothesis, whether perceptual grouping is reduced in hands-proximal space. Consistent with previous work on the object-based capture of attention, a benefit for the visual object in the hands-distal condition was observed in the present study. Interestingly, the object-based benefit did not emerge in the hands-proximal condition, suggesting perceptual grouping is impaired near the hands. This change in perceptual grouping processes provides further support for the hypothesis that visual processing near the hands is subject to increased magnocellular processing.

The limb-specific embodiment of a tool following experience.

The present study was designed to investigate the incorporation of tools into the human body schema. Previous research on tool use suggests that through physical interaction with a tool, the representation of the body is adjusted to incorporate or "embody" the tool. The present experiment was conducted to test the limb-specific nature of tool embodiment. Participants were presented with images of a person holding a rake and executed hand- and foot-press responses to colored targets superimposed on the hand, foot, and rake of the image. This task was completed before and after moving a ball around a course with a hand-held rake. Consistent with previous research, a body-part compatibility effect emerged-response times (RTs) were shorter when the responding limb and target location were compatible (e.g., hand responses to targets on the hand) than when they were incompatible (e.g., hand responses to targets on the foot). Of greater theoretical relevance, hand RTs to targets presented on the hand were shorter than those to targets on the rake prior to experience, but were not different after completing the rake task. The post-experience similarity in hand RTs emerged because there was a significant reduction in RTs to targets on the rake following use. There was no significant pre-/post-experience change in hand RTs to targets on the hand or, importantly, for any response executed by the foot. These results provide new evidence that a tool is embodied in a limb-specific manner and is represented within the body schema as if it was an extension of the limb.

Trajectory deviations in spatial compatibility tasks with peripheral and central stimuli.

It is widely held that the spatial compatibility effect emerges because the irrelevant spatial dimension of the target stimulus activates a response simultaneous to the activation of a response to the relevant stimulus dimension. The non-target response facilitates response planning on compatible trials, but interferes with response planning on incompatible trials. In support of this hypothesis, the trajectories of aiming movements executed on incompatible trials deviate in the direction of the stimulus location. These deviations are thought to occur because the characteristics of the simultaneously active target and non-target responses merge. Previously, target stimuli were presented at the target locations leaving open the possibility that the response activation and subsequent deviations were dependent on the stimulus-driven attentional capture associated with the dynamic change of stimulus onset. The present research was conducted to determine if attention capturing events at the target locations were necessary for the movement deviations to emerge by investigating if trajectory deviations are also observed when the spatial dimension is presented centrally. Participants in the Central condition aimed to left and right target locations based on the color of a ring worn on a finger that pointed toward the response locations. Similar to results from a Peripheral condition, trajectory deviations were observed in the Central condition. Although it is unclear if the deviations in the Central condition occurred because of attentional shifts driven by the cue or response preplanning, these results demonstrate that dynamic changes at target locations are sufficient, but not necessary, to generate trajectory deviations.

People are better at maximizing expected gain in a manual aiming task with rapidly changing probabilities than with rapidly changing payoffs.

Previous research has shown that humans can select movements that achieve their goals, while avoiding negative outcomes, by selecting an "optimal movement endpoint." This optimal endpoint is modeled based on the participants' endpoint variability and the payoffs associated with the target and penalty regions within the environment. Although the values associated with our goals vary on a moment-to-moment basis in our daily interactions, the adaptation of endpoint selection to changing payoffs in laboratory-based tasks has been examined by varying contexts between blocks of trials. The present study was designed to determine whether participants adjust endpoints and aim to optimal endpoints and whether performance differs when probability or payoff parameters change from trial to trial. Participants aimed to a target circle that was partially overlapped by a penalty circle. They received 100 points for hitting the target and lost points for hitting the penalty area. The magnitude of the penalty value or the distance between the centers of the circles (related to the probability of target and penalty contact) was changed randomly from trial to trial in separate blocks. Results revealed that participants shifted their endpoint and generally aimed optimally when the distance between the circles was varied but did not optimally shift their endpoints when the penalty value was varied. The results suggest that participants rapidly adapted endpoints when the probabilities associated with the task change, because the spatial parameters are an intrinsic property of the visual stimuli that are tightly linked with the motor system, whereas consistent feedback may be necessary to adjust to value parameters effectively.

Catching eyes: effects of social and nonsocial cues on attention capture.

Direct eye contact and motion onset are two powerful cues that capture attention. In the present study, we combined direct gaze with the sudden onset of motion to determine whether these cues have independent or shared influences. Participants identified targets presented randomly on one of four faces. Initially, two faces depicted direct gaze, and two faces depicted averted gaze. Simultaneously with or 900 ms before target presentation, one face with averted gaze switched to direct gaze, and one face with direct gaze switched to averted gaze. When gaze transitions and target presentation were simultaneous, the greatest response-time facilitation occurred at the location of the sudden onset of direct gaze. When target presentation was delayed, direct-gaze cues maintained a facilitatory influence, whereas motion cues induced an inhibitory influence. These findings reveal that gaze cues and motion cues at the same location influence information processing via independent and concurrently acting social and nonsocial attention channels.

Responses of the human motor system to observing actions across species: A transcranial magnetic stimulation study.

Ample evidence suggests that the role of the mirror neuron system (MNS) in monkeys is to represent the meaning of actions. The MNS becomes active in monkeys during execution, observation, and auditory experience of meaningful, object-oriented actions, suggesting that these cells represent the same action based on a variety of cues. The present study sought to determine whether the human motor system, part of the putative human MNS, similarly represents and reflects the meaning of actions rather than simply the mechanics of the actions. To this end, transcranial magnetic stimulation (TMS) of primary motor cortex was used to generate motor-evoked potentials (MEPs) from muscles involved in grasping while participants viewed object-oriented grasping actions performed by either a human, an elephant, a rat, or a body-less robotic arm. The analysis of MEP amplitudes suggested that activity in primary motor cortex during action observation was greatest during observation of the grasping actions of the rat and elephant, and smallest for the human and robotic arm. Based on these data, we conclude that the human action observation system can represent actions executed by non-human animals and shows sensitivity to species-specific differences in action mechanics.

Social gaze cueing elicits facilitatory and inhibitory effects on movement execution when the model might act on an object.

Social cues, such as eye gaze and pointing fingers, can increase the prioritisation of specific locations for cognitive processing. A previous study using a manual reaching task showed that, although both gaze and pointing cues altered target prioritisation (reaction times [RTs]), only pointing cues affected action execution (trajectory deviations). These differential effects of gaze and pointing cues on action execution could be because the gaze cue was conveyed through a disembodied head; hence, the model lacked the potential for a body part (i.e., hands) to interact with the target. In the present study, the image of a male gaze model, whose gaze direction coincided with two potential target locations, was centrally presented. The model either had his arms and hands extended underneath the potential target locations, indicating the potential to act on the targets (Experiment 1), or had his arms crossed in front of his chest, indicating the absence of potential to act (Experiment 2). Participants reached to a target that followed a nonpredictive gaze cue at one of three stimulus onset asynchronies. RTs and reach trajectories of the movements to cued and uncued targets were analysed. RTs showed a facilitation effect for both experiments, whereas trajectory analysis revealed facilitatory and inhibitory effects, but only in Experiment 1 when the model could potentially act on the targets. The results of this study suggested that when the gaze model had the potential to interact with the cued target location, the model's gaze affected not only target prioritisation but also movement execution.

Prolonged exposure to mixed reality alters task performance in the unmediated environment.

The popularity of mixed reality (MR) technologies, including virtual (VR) and augmented (AR) reality, have advanced many training and skill development applications. If successful, these technologies could be valuable for high-impact professional training, like medical operations or sports, where the physical resources could be limited or inaccessible. Despite MR's potential, it is still unclear whether repeatedly performing a task in MR would affect performance in the same or related tasks in the physical environment. To investigate this issue, participants executed a series of visually-guided manual pointing movements in the physical world before and after spending one hour in VR or AR performing similar movements. Results showed that, due to the MR headsets' intrinsic perceptual geometry, movements executed in VR were shorter and movements executed in AR were longer than the veridical Euclidean distance. Crucially, the sensorimotor bias in MR conditions also manifested in the subsequent post-test pointing task; participants transferring from VR initially undershoot whereas those from AR overshoot the target in the physical environment. These findings call for careful consideration of MR-based training because the exposure to MR may perturb the sensorimotor processes in the physical environment and negatively impact performance accuracy and transfer of training from MR to UR.

Modulation of response activation leads to biases in perceptuomotor decision making.

Humans are constantly enacting motor responses based on perceptual judgments or decisions. Recent work suggests that accumulating evidence for a decision and planning the action to enact the decision are coupled. Further, decision commitment may occur when the action reaches its motor threshold. Across several experiments, this coupled perception-action account of perceptuomotor decision making was tested by determining if increasing response activation corresponding to one decision influenced the evidence needed to make that decision. Participants were presented with stimuli that contained varying ratios of yellow-to-blue squares and made a speeded left/right-hand response to report whether the stimulus had more yellow or blue squares, respectively. Response activation was modulated by presenting stimuli laterally on the screen-spatially compatible or incompatible with the color reports. When stimuli appeared leftward (spatially compatible with a left response/"yellow" report), the threshold for a "yellow" perceptuomotor decision was reduced-consistent with the hypothesis that increasing "yellow" response activation would lead to a "yellow" reporting bias. Further, when stimuli appeared rightward (spatially compatible with a right response/"blue" report), the threshold for a "blue" perceptuomotor decision was reduced. An additional experiment revealed that directional saccades occurring during the task were unlikely to account for biases. Overall, spatially induced response activation influenced the decision outcomes, providing support for a tightly coupled perception-action system underlying perceptuomotor decisions. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

"The clothes (and the face) make the Starman": Facial and clothing features shape self-other matching processes between human observers and a cartoon character.

Anthropomorphization occurs when human characteristics are attributed to nonhuman animals or objects. One process that could facilitate the anthropomorphization of nonhuman animals may be a self-other body-part matching mechanism wherein the body of the nonhuman animal is conceptually mapped to the human observer's representation of their body. The present study was designed to determine if specific features could facilitate body-part matching between the cartoon of a nonhuman animal and human observers. Participants responded to targets presented on the cartoon of a starfish. In No Structure conditions, dots and curved lines were distributed evenly within the starfish. In Face conditions, two dots and one curved line represented eyes and a mouth of a "face". In Clothes conditions, dots and lines represented a shirt and pants. Body-part matching emerged when the image had a face or clothing, but did not emerge in No Structure conditions. These studies provide unique evidence that the anthropomorphization of a nonhuman cartoon may be facilitated by human-like internal features on the image.