Recognizing people from their movement

Human observers demonstrate impressive visual sensitivity to human movement. What defines this sensitivity? If motor experience influences the visual analysis of action, then observers should be most sensitive to their own movements. If view-dependent visual experience determines visual sensitivity to human movement, then observers should be most sensitive to the movements of their friends. To test these predictions, participants viewed sagittal displays of point-light depictions of themselves, their friends, and strangers performing various actions. In actor identification and discrimination tasks, sensitivity to one's own motion was highest. Visual sensitivity to friends', but not strangers', actions was above chance. Performance was action dependent. Control studies yielded chance performance with inverted and static displays, suggesting that form and low-motion cues did not define performance. These results suggest that both motor and visual experience define visual sensitivity to human action.     

Walking perception by walking observers

People frequently analyze the actions of other people for the purpose of action coordination. To understand whether such self-relative action perception differs from other-relative action perception, the authors had observers either compare their own walking speed with that of a point-light walker or compare the walking speeds of 2 point-light walkers. In Experiment 1, observers walked, bicycled, or stood while performing a gait-speed discrimination task. Walking observers demonstrated the poorest sensitivity to walking speed, suggesting that perception and performance of the same action alters visual-motion processes. Experiments 2-6 demonstrated that the processes used during self-relative and other-relative action perception differ significantly in their dependence on observers' previous motor experience, current motor effort, and potential for action coordination. These results suggest that the visual analysis of human motion during traditional laboratory studies can differ substantially from the visual analysis of human movement under more realistic conditions.     

Experts see it all: configural effects in action observation

Biological motion perception is influenced by observers’ familiarity with the observed action. Here, we used classical dance as a means to investigate how visual and motor experience modulates perceptual mechanism for configural processing of actions. Although some ballet moves are performed by only one gender, male and female dancers train together and acquire visual knowledge of all ballet moves. Twenty-four expert ballet dancers (12 female) and matched non-expert participants viewed pairs of upright and inverted point light female and common dance movements. Visual discrimination between different exemplars of the same movement presented upright was significantly better in experts than controls, whilst no differences were found when the same stimuli were presented upside down. These results suggest expertise influences configural action processing. Within the expert group, effects were stronger for female participants than for males, whilst no differences were found between movement types. This observer gender effect could suggest an additional role for motor familiarity in action perception, over and above the visual experience. Our results are consistent with a specific motor contribution to configural processing of action.     

Action goal selection and motor planning can be dissociated by tool use

The preparation of eye or hand movements enhances visual perception at the upcoming movement end position. The spatial location of this influence of action on perception could be determined either by goal selection or by motor planning. We employed a tool use task to dissociate these two alternatives. The instructed goal location was a visual target to which participants pointed with the tip of a triangular hand-held tool. The motor endpoint was defined by the final fingertip position necessary to bring the tool tip onto the goal. We tested perceptual performance at both locations (tool tip endpoint, motor endpoint) with a visual discrimination task. Discrimination performance was enhanced in parallel at both spatial locations, but not at nearby and intermediate locations, suggesting that both action goal selection and motor planning contribute to visual perception. In addition, our results challenge the widely held view that tools extend the body schema and suggest instead that tool use enhances perception at those precise locations which are most relevant during tool action: the body part used to manipulate the tool, and the active tool tip.     

Interaction of Perception and Action in Discrete and Continuous Rapid Aiming Tasks

Previously, we have shown that discrete and continuous rapid aiming tasks are governed by distinct visuomotor control mechanisms by assessing the combined visual illusion effects on the perceived and effective index of difficulty (ID). All participants were perceptually biased by the combined visual illusion before they performed the rapid aiming tasks. In the current study, the authors manipulated the order of performing perceptual and motor tasks to examine whether perceptual or motor experience with the illusory visual target would influence the subsequent perceived and effective ID in discrete and continuous tapping tasks. The results supported our hypothesis showing that perceptual experience with the illusory visual target in the discrete condition reduced the effective ID in the subsequent discrete tapping task, and motor experience with the illusory visual target in the continuous condition reduced the illusion effects on the perceived ID in the subsequent perceptual judgment task. The study demonstrates the coinfluence of perception and action, and suggests that perception and action influence one another with different magnitude depending on the spatial frame of reference used to perform the perceptuomotor task.     

The role of Broca's area in speech perception: evidence from aphasia revisited

Motor theories of speech perception have been re-vitalized as a consequence of the discovery of mirror neurons. Some authors have even promoted a strong version of the motor theory, arguing that the motor speech system is critical for perception. Part of the evidence that is cited in favor of this claim is the observation from the early 1980s that individuals with Broca’s aphasia, and therefore inferred damage to Broca’s area, can have deficits in speech sound discrimination. Here we re-examine this issue in 24 patients with radiologically confirmed lesions to Broca’s area and various degrees of associated non-fluent speech production. Patients performed two same-different discrimination tasks involving pairs of CV syllables, one in which both CVs were presented auditorily, and the other in which one syllable was auditorily presented and the other visually presented as an orthographic form; word comprehension was also assessed using word-to-picture matching tasks in both auditory and visual forms. Discrimination performance on the all-auditory task was four standard deviations above chance, as measured using d′, and was unrelated to the degree of non-fluency in the patients’ speech production. Performance on the auditory–visual task, however, was worse than, and not correlated with, the all-auditory task. The auditory–visual task was related to the degree of speech non-fluency. Word comprehension was at ceiling for the auditory version (97% accuracy) and near ceiling for the orthographic version (90% accuracy). We conclude that the motor speech system is not necessary for speech perception as measured both by discrimination and comprehension paradigms, but may play a role in orthographic decoding or in auditory–visual matching of phonological forms.     

Sensory noise explains auditory frequency discrimination learning induced by training with identical stimuli

Thresholds in various visual and auditory perception tasks have been found to improve markedly with practice at intermediate levels of task difficulty. Recently, however, there have been reports that training with identical stimuli, which, by definition, were impossible to discriminate correctly beyond chance, could induce as much discrimination learning as could training with different stimuli. These surprising findings have been interpreted as evidence that discrimination learning can occur in the absence of perceived differences between stimuli and need not involve the fine-tuning of a discrimination mechanism. Here, we show that these counterintuitive findings of discrimination learning without discrimination can be understood simply by considering the effect of internal noise on sensory representations. Because of such noise, physically identical stimuli are unlikely to be perceived as being strictly identical. We show that, given empirically derived levels of sensory noise, perceived differences evoked by identical stimuli are actually not much smaller than those induced by the physical differences typically used in discrimination-learning experiments. We suggest that findings of discrimination learning with identical stimuli can be explained without implicating any fundamentally new learning mechanism.     

Distance perception during self-movement

The perception of distance in open fields was widely studied with static observers. However, it is a fact that we and the world around us are in continuous relative movement, and that our perceptual experience is shaped by the complex interactions between our senses and the perception of our self-motion. This poses interesting questions about how our nervous system integrates this multisensory information to resolve specific tasks of our daily life, for example, distance estimation. This study provides new evidence about how visual and motor self-motion information affects our perception of distance and a hypothesis about how these two sources of information can be integrated to calibrate the estimation of distance. This model accounts for the biases found when visual and proprioceptive information is inconsistent.     

The tunnel effect,Gibson's perception theory,and reflective seeing

Summary Subjects can have continuous visual experience of an object's movement across a display though the movement's middle phase takes place behind an opaque screen. The present article considers explanatory issues pertaining to this so-called, tunnel effect, with special reference to Gibson' s perception theory and the visual activity that I have been calling reflective seeing. Among the issues discussed are the following. (a) In the tunnel experiments, I suggest, there occur both persisting perception, as Michotte held, and persistence perception, as Gibson held. The subjects pick up stimulus information that allows visually experiencing the object's going out of sight at one edge of the screen and coming back into sight at another edge of the screen; the subjects have visual experience of the continued existence and movement of the object while it is out of sight. Moreover, persistence of perceptual experience is involved: when the object goes out of sight, the subjects' visual experience of its movement goes on. (b) I also argue that the tunnel effect is a phenomenon of both straightforward and reflective seeing. Adopting a phenomenal attitude, as one does when reporting one's perceptual experience, one still sees movement taking place on the other side of the screen, as one does in straightforward seeing. However, whereas straightforward seeing does not give inner awareness of visual experience, the subjects in the tunnel experiments report visually experiencing the object's movement while also visually experiencing the opaque screen in front of it as opaque. I argue that these reports, and those about the object's going out of and coming back into sight, must be based on the kind of visual experience that is part and product of reflective seeing.     

Voice-based assessments of trustworthiness,competence, and warmth in blind and sighted adults

The study of voice perception in congenitally blind individuals allows researchers rare insight into how a lifetime of visual deprivation affects the development of voice perception. Previous studies have suggested that blind adults outperform their sighted counterparts in low-level auditory tasks testing spatial localization and pitch discrimination, as well as in verbal speech processing; however, blind persons generally show no advantage in nonverbal voice recognition or discrimination tasks. The present study is the first to examine whether visual experience influences the development of social stereotypes that are formed on the basis of nonverbal vocal characteristics (i.e., voice pitch). Groups of 27 congenitally or early-blind adults and 23 sighted controls assessed the trustworthiness, competence, and warmth of men and women speaking a series of vowels, whose voice pitches had been experimentally raised or lowered. Blind and sighted listeners judged both men’s and women’s voices with lowered pitch as being more competent and trustworthy than voices with raised pitch. In contrast, raised-pitch voices were judged as being warmer than were lowered-pitch voices, but only for women’s voices. Crucially, blind and sighted persons did not differ in their voice-based assessments of competence or warmth, or in their certainty of these assessments, whereas the association between low pitch and trustworthiness in women’s voices was weaker among blind than sighted participants. This latter result suggests that blind persons may rely less heavily on nonverbal cues to trustworthiness compared to sighted persons. Ultimately, our findings suggest that robust perceptual associations that systematically link voice pitch to the social and personal dimensions of a speaker can develop without visual input.     

Perception of biological motion from limited-lifetime stimuli

The visual perception of human movement from sparse point-light walkers is often believed to rely on local motion analysis. We investigated the role of local motion in the perception of human walking, viewed from the side, in different tasks. The motion signal was manipulated by varying point lifetime. We found the task of coherence discrimination, commonly used in biological motion studies, to be inappropriate for testing the role of motion. A task requiring temporal information showed a strong performance drop when fewer points were used or when the image sequence was sampled and displayed at a reduced frame rate. Irrespective of the frame rate, performance did not vary with point lifetime. We concluded that local motion is not required for the perception of tested biological movements, suggesting that the analysis of biological motion does not benefit from examining local motion. The reliance of perception on the number of displayed points and frames supports the idea that biological motion is perceived from a sequence of spatiotemporally sampled forms.     

Psychometrically matched visual-processing tasks in schizophrenia spectrum disorders

Patients with schizophrenia show deficits in visual perception and working memory, but the relationship between these deficits has not been characterized with psychometrically matched tasks. The authors administered 2 visual discrimination and 6 recognition tasks to 43 schizophrenia spectrum patients and 22 nonpsychiatric subjects. When performing difficulty-matched tasks, spectrum subjects showed more severe impairments for motion compared with form processing. When tasks were matched on true score variance, spectrum subjects exhibited worse performance on both form and motion discrimination, and a differential deficit in motion recognition with a short display duration and long interstimulus interval. These results provide evidence of differential deficits in visual processing in schizophrenia that appear to be dependent on the temporal characteristics of the tasks.     

Keeping an eye on the violinist: motor experts show superior timing consistency in a visual perception task

Common coding theory states that perception and action may reciprocally induce each other. Consequently, motor expertise should map onto perceptual consistency in specific tasks such as predicting the exact timing of a musical entry. To test this hypothesis, ten string musicians (motor experts), ten non-string musicians (visual experts), and ten non-musicians were asked to watch progressively occluded video recordings of a first violinist indicating entries to fellow members of a string quartet. Participants synchronised with the perceived timing of the musical entries. Results revealed significant effects of motor expertise on perception. Compared to visual experts and non-musicians, string players not only responded more accurately, but also with less timing variability. These findings provide evidence that motor experts’ consistency in movement execution—a key characteristic of expert motor performance—is mirrored in lower variability in perceptual judgements, indicating close links between action competence and perception.     

Duration discrimination in the context of age,sex, and cognition

It has been proposed that the perception of very short duration is governed by sensory mechanisms, whereas the perception of longer duration depends on cognitive capacities. Four duration discrimination tasks (modalities: visual, auditory; base duration: 100 ms, 1000 ms) were used to study the relation between time perception, age, sex, and cognitive abilities (alertness, visual and verbal working memory, general fluid reasoning) in 100 subjects aged between 21 and 84 years. Temporal acuity was higher (Weber fractions are lower) for longer stimuli and for the auditory modality. Age was related to the visual 100 ms condition only, with lower temporal acuity in elder participants. Alertness was significantly related to auditory and visual Weber fractions for shorter stimuli only. Additionally, visual working memory was a significant predictor for shorter visual stimuli. These results indicate that alertness, but also working memory, are associated with temporal discrimination of very brief duration.     

Effect of structuring the workspace on cognitive and sensorimotor distance estimation: no dissociation between perception and action

Independent processing of visual information for perception and action is supported by studies about visual illusions, which showed that context information influences overtjudgment but not reaching attempts. The objection was raised, however, that these two types of performance are notdirectly comparable, since they generally focus on different properties of the visual input. The goal of the present study was to quantify the influence of context information (in the form of a textured background) on the cognitive and sensorimotor processing of egocentric distance. We found that the subjective area comprising reachable objects (probed with a cognitive task) decreased, whereas the amplitude of reaching movement (probed with a sensorimotor task) increased in the presence of the textured background with both binocular and monocular viewing. Directional motor performance was not affected by the experimental conditions, but there was a tendency for the kinematic parameters to mimic trajectory variations. The similar but opposite effects of the textured background in the cognitive and sensorimotor tasks suggested that in both tasks the visual targets were perceived as closer when they were presented in a sparse environment. A common explanation for the opposite effects was confirmed by the percentage of background influence, which was highly correlated in the two tasks. We conclude that visual processing for perception and action cannot be dissociated from context influence, since it does not differ when the tasks entail the processing of similar spatial characteristics.     

TASK DIFFICULTY AND ABERRANT BEHAVIOR IN SEVERELY HANDICAPPED STUDENTS

The influence of task difficulty on aberrant behavior was investigated with three severely handicapped students. Noticeably higher rates of problem behavior occurred in demand compared to no-demand conditions. In addition, there were higher rates of problem behaviors on difficult versus easy tasks. Both these findings were validated with visual discrimination and perceptual motor tasks. An errorless learning procedure effectively minimized errors and aberrant behavior in visual discrimination tasks but not in perceptual motor tasks. It was conceptualized that aberrant behavior was maintained by negative reinforcement contingencies. Difficult tasks were aversive to the children, who emitted aberrant responses to escape or avoid such tasks. By contrast, conditions in which no demands were made, easy tasks, and, in visual discrimination learning, errorless tasks, were less aversive and resulted in little or no problem behavior. Implications for reducing maladaptive behaviors through curricular modifications are discussed and contrasted to more traditional consequence manipulation approaches.     

The effects of method of measurement upon children''s performance on visual perceptual tasks

Sixty-four first-grade children of average or above intelligence who did not evidence visual perceptual dysfunction were administered a series of visual perceptual tasks. The tasks evaluated the skills of visual figure-ground perception and form discrimination and involved four methods of measurement of these abilities: tachistoscopic, untimed, naming, and recognition. Results indicated considerable method of measurement influence upon task performance. Implications of the results for both researchers and practitioners are discussed.     

非数量视觉特征对数量感知的影响

以往许多研究探讨了各种视觉特征对数量判断任务的影响,但得出了不一致的结论.本研究依据信号检测论原理对刺激特征影响数量判断的方式进行考察.结果发现:刺激大小、形状和分布均匀度等因素可影响数量判断的反应标准,但不会影响辨别力;刺激聚集或组块会直接对数量判断的辨别力产生影响.结果表明,不同刺激特征对数量判断的影响方式存在差异.一方面,人类具有从刺激特征中直接抽取数量信息进行认知比较的能力;另一方面,刺激点聚集或组块可以直接影响被试的数量感知.此外,我们还推测,组块是通过改变客体表征的方式来影响数量感知的.     

Visual speech processing: Word-decoding and word-discrimination related to sentence-based speechreading and hearing-impairment

Two aspects of visual speech processing in speechreading (word decoding and word discrimination) were tested in a group of 24 normal hearing and a group of 20 hearing-impaired subjects. Word decoding and word discrimination performance were independent of factors related to the impairment, both in a quantitative and a qualitative sense. Decoding skill, but not discrimination skill, was associated with sentence-based speechreading. The results were interpreted such that, in order to represent a critical component process in sentence-based speechreading, the visual speech perception task must entail lexically induced processing as a task-demand. The theoretical status of the word decoding task as one operationalization of a speech decoding module was discussed (Fodor, 1983). An error analysis of performance in the word decoding/discrimination tasks suggested that the perception of heard stimuli, as well as the perception of lipped stimuli, were critically dependent on the same features; that is, the temporally initial phonetic segment of the word (cf. Marslen-Wilson, 1987). Implications for a theory of visual speech perception were discussed.     

Advances in graphonomics: studies on fine motor control, its development and disorders

During the past 20 years graphonomic research has become a major contributor to the understanding of human movement science. Graphonomic research investigates the relationship between the planning and generation of fine motor tasks, in particular, handwriting and drawing. Scientists in this field are at the forefront of using new paradigms to investigate human movement. The 16 articles in this special issue of Human Movement Science show that the field of graphonomics makes an important contribution to the understanding of fine motor control, motor development, and movement disorders. Topics discussed include writer's cramp, multiple sclerosis, Parkinson's disease, schizophrenia, drug-induced parkinsonism, dopamine depletion, dysgraphia, motor development, developmental coordination disorder, caffeine, alertness, arousal, sleep deprivation, visual feedback transformation and suppression, eye-hand coordination, pen grip, pen pressure, movement fluency, bimanual interference, dominant versus non-dominant hand, tracing, freehand drawing, spiral drawing, reading, typewriting, and automatic segmentation.