The pigeon's discrimination of movement patterns (Lissajous figures) and contour-dependent rotational invariance

The ability of pigeons to discriminate complex motion patterns was investigated with the aid of moving Lissajous figures. The pigeons successfully learned to differentiate two successively presented cyclic trajectories of a single moving dot. This suggests that they can recognize a movement Gestalt when information about shape is minimal. They also quickly learned a new discrimination between moving-outline stimuli with repetitively changing contour patterns. Contrasting results were obtained when the dot or outline stimuli were axis-rotated through 90 degrees. Rotational invariance of pattern discrimination was clearly demonstrated only when moving contours were visible. Nevertheless, pigeons could discriminate the axis-orientation of a moving-dot or moving-outline pattern when trained to do so. Discrimination did not seem to depend on single parameters of motion but rather on the recognition of a temporally integrated movement Gestalt. The visual system of pigeons, as well as that of humans, may be well adapted to recognize the types of oscillatory movements that represent components of the motor behaviour shown by many living organisms.     

Interference effects demonstrate distinct roles for visual and motor imagery during the mental representation of human action

Four experiments were completed to characterize the utilization of visual imagery and motor imagery during the mental representation of human action. In Experiment 1, movement time functions for a motor imagery human locomotion task conformed to a speed-accuracy trade-off similar to Fitts' Law, whereas those for a visual imagery object motion task did not. However, modality-specific interference effects in Experiment 2 demonstrate visual and motor imagery as cooperative processes when the action represented is tied to visual coordinates in space. Biomechanic-specific motor interference effects found in Experiment 3 suggest one basis for separation of processing channels within motor imagery. Finally, in Experiment 4 representations of motor actions were found to be generated using only visual imagery under certain circumstances: namely, when the imaginer represented the motor action of another individual while placed at an opposing viewpoint. These results suggest that the modality of representation recruited to generate images of human action is dependent on the dynamic relationship between the individual, movement, and environment.     

Top-down social modulation of interpersonal observation–execution

Cyclical upper limb movement can involuntarily deviate from its primary movement axis when the performer concurrently observes incongruent biological motion (i.e. interpersonal observation–execution). The current study examined the social modulation of such involuntary motor interference using a protocol that reflected everyday social interactions encountered in a naturalistic social setting. Eighteen participants executed cyclical horizontal arm movements during the observation of horizontal (congruent) or curvilinear (incongruent) biological motion. Both prior to, and during the interpersonal observation–execution task, participants also received a series of social words designed to prime a pro-social or anti-social attitude. The results showed greater orthogonal movement deviation, and thus interference, for the curvilinear compared to horizontal stimuli. Importantly, and opposite to most of the previous findings from work on automatic imitation and mimicry, there was a greater interference effect for the anti-social compared to pro-social prime condition. These findings demonstrate the importance of interpreting the context of social primes, and strongly support predictions of a comparison between the prime construct and the self-concept/-schema and the top-down response modulation of social incentives.     

The temporal dynamics of the perceptual consequences of action-effect prediction

An essential aspect of voluntary action control is the ability to predict the perceptual effects of our actions. Although the influence of action-effect prediction on humans’ behavior and perception is unequivocal, it remains unclear when action-effect prediction is generated by the brain. The present study investigates the dynamics of action effect anticipation by tracing the time course of its perceptual consequences. Participants completed an acquisition phase during which specific actions (left and right key-presses) were associated with specific visual effects (upward and downward dots motion). In the test phase they performed a 2 AFC identification task in which they were required to indicate whether the dots moved upward or downward. To isolate any effects of action-effect prediction on perception, participants were presented with congruent and incongruent dot motion in which the association participants learned in the previous acquisition phase was respected and violated, respectively. Crucially, to assess the temporal dynamics of action prediction, congruent and incongruent stimuli were presented at different intervals before or after action execution. We observed higher sensitivity (d′) to motion discrimination in congruent vs. incongruent trials only when stimuli were presented from about 220 ms before the action to 280 ms after the action. The temporal dynamics of our effect suggest that action-effect prediction modulates perception at later stages of motor preparation.     

Pictures of you: Dot stimuli cause motor contagion in presence of a still human form

In this study, we investigate which visual cues induce participants to encode a non-human motion stimulus in their motor system. Participants performed reach-to-grasp actions to a target after observing a dot moving in a direct or higher-arcing path across a screen. Dot motion occurred in the presence of a meaningless (scrambled human model) stimulus, a still human model, or a human model performing a direct or exaggeratedly curved reach to a target. Our results show that observing the dot displacement causes motor contagion (changes in the height of the observer’s hand trajectory) when a human form was visually present in the background (either moving or still). No contagion was evident, however, when this human context was absent (i.e., human image scrambled and not identifiable). This indicates that visual cues suggestive of human agency can determine whether or not moving stimuli are encoded in the motor system.     

Some considerations about the biological appearance of pacing stimuli in visuomotor finger-tapping tasks

Sensorimotor synchronization is a crucial function for human daily activities, which relies on the ability of predicting external events. Synchronization performance, as assessed in finger-tapping (FT) tasks, is characterized by an anticipation tendency, as the tap generally precedes the pacing event. This synchronization error (SE) depends on many factors, in particular on the features of the pacing stimulus. Interest is growing in the facilitation effect that action observation has on motor execution. So far, neuroimaging and neurophysiology studies of motor priming via action observation have mainly employed tasks requiring single action instances. The impact of action observation on motor synchronization to periodic stimuli has not yet been tested; to this aim, a synchronization FT task may be an eligible probing task. The purpose of this study was to characterize a biological pacer at the behavioral level and provide information for those interested in studying the brain processes of continuous observation/execution coupling in timed actions using FT tasks. We evaluated the influence of the biological appearance of a pacer (a tapping finger) on SE, when compared to an abstract, kinematically equivalent pacer (a tilting hinged bar) and a more standard stimulus (a pulsating dot). We showed that the continuous visual display of a biological pacer yields comparable results to the abstract pacer, and a more robust performance and larger anticipations than a traditional pulsating stimulus.     

Perception of elliptic biological motion

We tested the ability of the mature visual system for discrimination between types of elliptic biological motion on the basis of event kinematics. Healthy adult volunteers were presented with point-light displays depicting elliptic motion when only a single dot, a moving point-light arm, or a whole point-light human figure was visible. The displays were created in accordance with the two-thirds power kinematic law (natural motion), whereas the control displays violated this principle (unnatural motion). On each trial, participants judged whether the display represented natural or unnatural motion. The findings indicate that adults are highly sensitive to violation of the two-thirds power kinematic law. Notably, participants can easily discriminate between natural and unnatural motions without recognising the stimuli, which suggests that people implicitly use kinematic information. Most intriguing, event recognition seems to diminish the capacity to judge whether event kinematics is unnatural. We discuss possible ways for a cross-talk between perception and production of biological movement, and the brain mechanisms involved in biological motion processing.     

The effect of spatial orientation on the perception of moving tactile stimuli

Previous studies have shown that the perception of spatial patterns, such as letters, presented to the hand is affected by the spatial orientation of the hand. The present study investigated how the perception of direction of motion across the fingerpads changes with the position of the hand in space. The moving stimuli were generated on two displays. In one condition, the displays were placed horizontally in front of the subject, with the subject’s thumb (target site) and index finger (nontarget site) placed flat on the displays. In a second condition, the displays were vertically oriented and gripped between the thumb and index finger. Using a selective-attention paradigm in which subjects are instructed to respond only to the direction of motion at the target site, performance was still affected by the direction of motion at the nontarget site. Changing the orientation of the displays changed the effectiveness of the nontarget in interfering with the identification of the target movement. Nontarget stimuli that produced no interference in the horizontal orientation did so in the vertical, and vice versa. It appears that subjects are not using the local direction of movement across the fingerpads to judge the relative direction of movement at the two sites; rather, they are using the external direction of movement.     

Exploring visuomotor priming following biological and non-biological stimuli

Observation of human actions influences the observer’s own motor system, termed visuomotor priming, and is believed to be caused by automatic activation of mirror neurons. Evidence suggests that priming effects are larger for biological (human) as opposed to non-biological (object) stimuli and enhanced when viewing stimuli in mirror compared to anatomical orientation. However, there is conflicting evidence concerning the extent of differences between biological and non-biological stimuli, which may be due to stimulus related confounds. Over three experiments, we compared how visuomotor priming for biological and non-biological stimuli was affected over views, over time and when attention to the moving stimulus was manipulated. The results indicated that the strength of priming for the two stimulus types was dependent on attentional location and load. This highlights that visuomotor priming is not an automatic process and provides a possible explanation for conflicting evidence regarding the differential effects of biological and non-biological stimuli.     

Unimodal and crossmodal effects of endogenous attention to visual and auditory motion

Three experiments were conducted examining unimodal and crossmodal effects of attention to motion. Horizontally moving sounds and dot patterns were presented and participants’ task was to discriminate their motion speed or whether they were presented with a brief gap. In Experiments 1 and 2, stimuli of one modality and of one direction were presented with a higher probability ( p = .7) than other stimuli. Sounds and dot patterns moving in the expected direction were discriminated faster than stimuli moving in the unexpected direction. In Experiment 3, participants had to respond only to stimuli moving in one direction within the primary modality, but to all stimuli regardless of their direction within the rarer secondary modality. Stimuli of the secondary modality moving in the attended direction were discriminated faster than were oppositely moving stimuli. Results suggest that attending to the direction of motion affects perception within vision and audition, but also across modalities.     

Preserved and Impaired Detection of Structure From Motion by a 'Motion-blind" Patient

Following bilateral extrastriate damage to areas that include the suspected human homologue of V5/MT, the patient LM has a specific deficit in processing moving stimuli. She has difficulty detecting the movement or coding the velocity of single moving dots. Nevertheless, we find that she can report human actions in Johansson “biological motion ”; displays. This requires the accurate coding of the direction and velocity of many moving dots. The implication is that structure can be extracted from motion in regions of visual cortex other than those traditionally associated with motion processing. However, she cannot report the spatial disposition of the actors whose actions she has recognized, not their movement in depth relative to her. A possible interpretation is that coding in these additional regions is primarily object-centred. Adding a small number of random stationary “noise” dots to the display prevents her from identifying the actions, suggesting that segregation by motion is implemented within the traditional movement areas.     

The effect of experience and of dots’ density and duration on the detection of coherent motion in dogs

Knowledge about the mechanisms underlying canine vision is far from being exhaustive, especially that concerning post-retinal elaboration. One aspect that has received little attention is motion perception, and in spite of the common belief that dogs are extremely apt at detecting moving stimuli, there is no scientific support for such an assumption. In fact, we recently showed that dogs have higher thresholds than humans for coherent motion detection (Kanizsar et al. in Sci Rep UK 7:11259, 2017). This term refers to the ability of the visual system to perceive several units moving in the same direction, as one coherently moving global unit. Coherent motion perception is commonly investigated using random dot displays, containing variable proportions of coherently moving dots. Here, we investigated the relative contribution of local and global integration mechanisms for coherent motion perception, and changes in detection thresholds as a result of repeated exposure to the experimental stimuli. Dogs who had been involved in the previous study were given a conditioned discrimination task, in which we systematically manipulated dot density and duration and, eventually, re-assessed our subjects’ threshold after extensive exposure to the stimuli. Decreasing dot duration impacted on dogs’ accuracy in detecting coherent motion only at very low duration values, revealing the efficacy of local integration mechanisms. Density impacted on dogs’ accuracy in a linear fashion, indicating less efficient global integration. There was limited evidence of improvement in the re-assessment but, with an average threshold at re-assessment of 29%, dogs’ ability to detect coherent motion remains much poorer than that of humans.     

Auditory clicks distort perceived velocity but only when the system has to rely on extraretinal signals

Previous work has found that repetitive auditory stimulation (click trains) increases the subjective velocity of subsequently presented moving stimuli. We ask whether the effect of click trains is stronger for retinal velocity signals (produced when the target moves across the retina) or for extraretinal velocity signals (produced during smooth pursuit eye movements, when target motion across the retina is limited). In Experiment 1, participants viewed leftward or rightward moving single dot targets, travelling at speeds from 7.5 to 17.5 deg/s. They estimated velocity at the end of each trial. Prior presentation of auditory click trains increased estimated velocity, but only in the pursuit condition, where estimates were based on extraretinal velocity signals. Experiment 2 generalized this result to vertical motion. Experiment 3 found that the effect of clicks during pursuit disappeared when participants tracked across a visually textured background that provided strong local motion cues. Together these results suggest that auditory click trains selectively affect extraretinal velocity signals. This novel finding suggests that the cross-modal integration required for auditory click trains to influence subjective velocity operates at later stages of processing.     

Biological movements look uniform: evidence of motor-perceptual interactions.

Six experiments demonstrate a visual dynamic illusion. Previous work has shown that in 2-dimensional (2D) drawing movements, tangential velocity and radius of curvature covary in a constrained manner. The velocity of point stimuli is perceived as uniform if and only if this biological constraint is satisfied. The illusion is conspicuous: The variations of velocity in the stimuli exceed 200%. Yet movements are perceived as uniform. Conversely, 2D stimuli moving at constant velocity are perceived as strongly nonuniform. The illusion is robust: Exposure to true constant velocity fails to suppress it. Results cannot be explained entirely by the kinetic depth effect. The illusion is evidence of a coupling between motor and perceptual processes: Even in the absence of any intention to perform a movement, certain properties of the motor system implicitly influence perceptual interpretation of the visual stimulus.     

Motor priming by movement observation with contralateral concurrent action execution

In the present study, the influence of simultaneous action execution on motor priming was investigated during movement observation using a simple-reaction task. Although previous studies have reported various effects of priming on motor performance, it has not yet been clarified how an additional source conveying kinetic information would modulate the priming effects. In the experiment, participants were asked to respond to an auditory cue by flexing their wrist while observing a line movement, which was slowly swinging like an inverted pendulum. In addition to the observation of line movement, the participants executed wrist flexion-extension actions synchronizing with line movement. The hand involved in pre-response wrist action varied with the priming condition: no movement execution (observation only), contralateral hand, and ipsilateral hand. In the contralateral condition, the stimulus-response congruency of movement direction was conflicted depending on the frame of reference (visual vs. anatomical coordinates). We found that all three priming conditions produced the compatibility effect, and the effect size did not differ between them. Importantly, in the contralateral condition, participants responded faster when the direction of line movement was congruent with the response movement in the anatomical coordinates. That is, the reaction time was shorter when pre-response action execution was in the flexion phase, even though the direction of observed movement and the response action were incongruent from the participants’ view. These results suggest that kinetic information has a great contribution to the motor priming system, which can reverse the vision-based compatibility effect.     

Predictable and self-initiated visual motion is judged to be slower than computer generated motion

Self-initiated action effects are often perceived as less intense than identical but externally generated stimuli. It is thought that forward models within the sensorimotor system pre-activate cortical representations of predicted action effects, reducing perceptual sensitivity and attenuating neural responses. As self-agency and predictability are seldom manipulated simultaneously in behavioral experiments, it is unclear if self-other differences depend on predictable action effect contingencies, or if both self- and externally generated stimuli are modulated similarly by predictability. We factorially combined variation in (1) predictability of action effects, (2) spatial congruence, and (3) performance by the self or computer to dissociate these influences on a visual discrimination task. Participants performed 2AFC speed judgments. Self-initiated motion was judged to be slower than computer-initiated motion when action effect contingencies were predictable, while spatial congruence influenced speed judgments only when action effect contingencies were unpredictable. Results are discussed in relation to current theories of sensory attenuation.     

Additivity of retinal and pursuit velocity in the perceptions of depth and rigidity from object-produced motion parallax

Two psychophysical experiments were conducted to investigate the mechanism that generates stable depth structure from retinal motion combined with extraretinal signals from pursuit eye movements. Stimuli consisted of random dots that moved horizontally in one direction (ie stimuli had common motion on the retina), but at different speeds between adjacent rows. The stimuli were presented with different speeds of pursuit eye movements whose direction was opposite to that of the common retinal motion. Experiment 1 showed that the rows moving faster on the retina appeared closer when viewed without eye movements; however, they appeared farther when pursuit speed exceeded the speed of common retinal motion. The 'transition' speed of the pursuit eye movement was slightly, but consistently, larger than the speed of common retinal motion. Experiment 2 showed that parallax thresholds for perceiving relative motion between adjacent rows were minimum at the transition speed found in experiment 1. These results suggest that the visual system calculates head-centric velocity, by adding retinal velocity and pursuit velocity, to obtain a stable depth structure.     

The influence of environmental context in interpersonal observation–execution

Cyclical upper-limb movements involuntarily deviate from a primary movement direction when the actor concurrently observes incongruent biological motion. We examined whether environmental context influences such motor interference during interpersonal observation–execution. Participants executed continuous horizontal arm movements while observing congruent horizontal or incongruent curvilinear biological movements with or without the presence of an object positioned as an obstacle or distractor. When participants were observing a curvilinear movement, an object located within the movement space became an obstacle, and, thus, the curvilinear trajectory was essential to reach into horizontal space. When acting as a distractor, or with no object, the curvilinear trajectory was no longer essential. For observing horizontal movements, objects were located at the same relative locations as in the curvilinear movement condition. We found greater involuntary movement deviation when observing curvilinear than horizontal movements. Also, there was an influence of context only when observing horizontal movements, with greater deviation exhibited in the presence of a large obstacle. These findings suggest that the influence of environmental context is underpinned by the (mis-)matching of observed and executed actions as incongruent biological motion is primarily coded via bottom-up sensorimotor processes, whilst the congruent condition incorporates surrounding environmental features to modulate the bottom-up sensorimotor processes.     

The influence of action observation on action execution: Dissociating the contribution of action on perception,perception on action,and resolving conflict

For more than 15 years, motor interference paradigms have been used to investigate the influence of action observation on action execution. Most research on so-called automatic imitation has focused on variables that play a modulating role or investigated potential confounding factors. Interestingly, furthermore, a number of functional magnetic resonance imaging (fMRI) studies have tried to shed light on the functional mechanisms and neural correlates involved in imitation inhibition. However, these fMRI studies, presumably due to poor temporal resolution, have primarily focused on high-level processes and have neglected the potential role of low-level motor and perceptual processes. In the current EEG study, we therefore aimed to disentangle the influence of low-level perceptual and motoric mechanisms from high-level cognitive mechanisms. We focused on potential congruency differences in the visual N190 ? a component related to the processing of biological motion, the Readiness Potential ? a component related to motor preparation, and the high-level P3 component. Interestingly, we detected congruency effects in each of these components, suggesting that the interference effect in an automatic imitation paradigm is not only related to high-level processes such as self-other distinction but also to more low-level influences of perception on action and action on perception. Moreover, we documented relationships of the neural effects with (autistic) behavior.     

Discrimination of intentional and random motion paths by pigeons

Twelve pigeons (Columba livia) were trained on a go/no-go schedule to discriminate between two kinds of movement patterns of dots, which to human observers appear to be "intentional" and "non-intentional" movements. In experiment 1, the intentional motion stimulus contained one dot (a "wolf") that moved systematically towards another dot as though stalking it, and three distractors ("sheep"). The non-intentional motion stimulus consisted of four distractors but no stalker. Birds showed some improvement of discrimination as the sessions progressed, but high levels of discrimination were not reached. In experiment 2, the same birds were tested with different stimuli. The same parameters were used but the number of intentionally moving dots in the intentional motion stimulus was altered, so that three wolves stalked one sheep. Despite the enhanced difference of movement patterns, the birds did not show any further improvement in discrimination. However, birds for which the non-intentional stimulus was associated with reward showed a decline in discrimination. These results indicated that pigeons can discriminate between stimuli that do and do not contain an element that human observer see as moving intentionally. However, as no feature-positive effect was found in experiment 1, it is assumed that pigeons did not perceive or discriminate these stimuli on the basis that the intentional stimuli contained a feature that the non-intentional stimuli lacked, though the convergence seen in experiment 2 may have been an effective feature for the pigeons. Pigeons seem to be able to recognise some form of multiple simultaneously goal-directed motions, compared to random motions, as a distinctive feature, but do not seem to use simple "intentional" motion paths of two geometrical figures, embedded in random motions, as a feature whose presence or absence differentiates motion displays. Electronic Publication