Human and machine perception of biological motion

More than 30 years ago, Johansson was the first to show that humans are capable of recovering information about the identity and activity of animate creatures rapidly and reliably from very sparse visual inputs – the phenomenon of biological motion. He filmed human actors in a dark setting with just a few strategic points on the body marked by lights – so-called moving light displays (MLDs). Subjects viewing the MLDs reported a vivid impression of moving human forms, and were even able to tell the activity in which the perceived humans were engaged. Subsequently, the phenomenon has been widely studied and many attempts have been made to model and to understand it. Typical questions that arise are: How precisely is the sparse low-level information integrated over space and time to produce the global percept, and how important is world knowledge (e.g., about animal form, locomotion, gravity, etc.)? In an attempt to answer such questions, we have implemented a machine-perception model of biological motion. If the computational model can replicate human data then it might offer clues as to how humans achieve the task. In particular, if it can do so with no or minimal world knowledge then this knowledge cannot be essential to the perception of biological motion. To provide human data for training and against which to assess the model, an extensive psychophysical experiment was undertaken in which 93 subjects were shown 12 categories of MLDs (e.g., normal, walking backwards, inverted, random dots, etc.) and were asked to indicate the presence or absence of natural human motion. Machine perception models were then trained on normal sequences as positive data and random sequences as negative data. Two models were used: a k-nearest neighbour (k-NN) classifier as an exemplar of ‘lazy’ learning and a back-propagation neural network as an exemplar of ‘eager’ learning. We find that the k-NN classifier is better able to model the human data but it still fails to represent aspects of knowledge about body shape (especially how relative joint positions change under rotation) that appear to be important to human judgements.     

Dorsal stream deficits suggest hidden dyslexia among deaf poor readers: correlated evidence from reduced perceptual speed and elevated coherent motion detection thresholds

Prelingual deafness and developmental dyslexia have confounding developmental effects on reading acquisition. Therefore, standard reading assessment methods for diagnosing dyslexia in hearing people are ineffective for use with deaf people. Recently, Samar, Parasnis, and Berent (2002) reported visual evoked potential evidence that deaf poor readers, compared to deaf good readers, have dorsal stream visual system deficits like those previously found for hearing dyslexics. Here, we report new psychometric and psychophysical evidence that deficits in dorsal stream function, likely involving extrastriate area MT, are associated with relatively poor reading comprehension in deaf adults. Poorer reading comprehension within a group of 23 prelingually deaf adults was associated with lower scores on the Symbol Digit Modality Test, a perceptual speed test commonly used to help identify dyslexia in hearing people. Furthermore, coherent dot motion detection thresholds, which reflect the functional status of area MT, correlated negatively with reading scores in each visual quadrant. Elevated motion thresholds for deaf poor readers were not due to general cognitive differences in IQ but were specifically correlated with poor perceptual speed. With IQ controlled, a highly reliable right visual field advantage for coherent motion detection was found. Additional analyses suggested that the functional status of dorsal stream motion detection mechanisms in deaf people is related to reading comprehension, but the direction and strength of lateralization of those mechanisms is independent of reading comprehension. Our results generally imply that dyslexia is a hidden contributor to relatively poor reading skill within the deaf population and that assessment of dorsal stream function may provide a diagnostic biological marker for dyslexia in deaf people.     

Changes in Saccadic and Manual Motor Control After Ocular Smooth Pursuit Adaptive Modifications

The gain of ocular smooth pursuit responses can be adaptively modified under certain circumstances. Evidence that these modifications are caused, at least partly, by changes at a sensory level comes from the fact that subsequent manual tracking movements generated during visual fixation are also modified in a similar manner. The question addressed in the present experiment was whether the modifications are constrained specifically to responses such as these, which are driven by retinal image motion, or whether they can also influence movements that make use of retinal image position. This was accomplished by comparing manual and oculomotor responses to step changes in target position before and after smooth pursuit adaptation. The results showed that, as with manual tracking movements, these responses were also modified by the adaptive procedure, although to a lesser extent. In particular, following a 20-min period in which subjects (N = 4) were submitted to a procedure designed to increase the gain of the smooth pursuit system, manual step tracking movements and ocular saccades displayed larger amplitudes than those shown prior to the adaptation. In addition, these gain changes were accompanied by appropriate alterations in response kinematics. Taken together, these results suggest that the mechanisms responsible for adaptive modifications in the smooth pursuit system are also able to more generally influence the processing of visuospatial information. The possible neurophysiological substrate underlying these mechanisms is discussed.     

面孔识别动态增益效应研究综述

近年来,研究者围绕动态面孔识别中的动态增益效应开展了一系列的研究。本文围绕面孔熟悉程度和面孔的活动类型两个方面对与动态增益效应有关的一系列动态面孔认知研究进行了总结,并对不同研究的差异进行了比较和分析。最后,对动态面孔认知规律、眼动模式和脑机制等研究方向上的发展进行了展望。     

Régulations endogène et exogène des émotions : des processus complémentaires et indissociables

Studies dealing with emotion regulation have known a fast expansion during the last twenty years. Yet, they are most often based on models centered on endogenous cognitive and behavioral processes as well as the pursuit of welfare, and do not consider the social aspect of emotions and emotion expression which elicit exogenous emotion regulation processes from social interaction partners. The goal of this article is to show that both endogenous and exogenous emotion regulation processes are complementary and indivisible, and to suggest working hypotheses about how they connect. In the first part of this document, after a quick reminder of the different theoretical approaches of (individual) endogenous emotion regulation, we emphasize works about social approach behaviors (social affiliation) in emotional situations. These studies report that social interactions are sometimes sought as they would allow for the endogenous implementation of interpersonal emotion regulation strategies, especially by means of emotion expression. Individual and interpersonal endogenous emotion regulation processes would then complementarily modify the emotions experienced by an individual faced with a critical situation. The second part of this article underlines that social interaction partners actually are operators of exogenous emotion regulation processes rather than passive reservoirs of resources an individual may pick up to regulate their emotions. For that purpose, we especially consider the ways relatives (directly or indirectly, explicitly or implicitly) constrain the social affiliation behaviors and emotion expressions of an individual who experiences emotions. Thus, we argue that those behaviors are strongly influenced not only by the nature and intensity of emotions, but also by: firstly, social learning about how to feel, what to express and how to regulate emotions in a specific situation; secondly, features of the social environment as well as social expectations and demands about sharing emotions versus inhibiting their expression; and thirdly, the exogenous emotion regulation strategies a partner may use to regulate an individual's emotions. This set of studies entices us to consider endogenous and exogenous emotion regulation processes as acting jointly to promote not only the adaptation to emotional situations, but also the quality of social bonds between members of a social network. Social integration is thus central in the study of emotion regulation processes.     

Walk this way: approaching bodies can influence the processing of faces

A highly familiar type of movement occurs whenever a person walks towards you. In the present study, we investigated whether this type of motion has an effect on face processing. We took a range of different 3D head models and placed them on a single, identical 3D body model. The resulting figures were animated to approach the observer. In a first series of experiments, we used a sequential matching task to investigate how the motion of an approaching person affects immediate responses to faces. We compared observers’ responses following approach sequences to their performance with figures walking backwards (receding motion) or remaining still. Observers were significantly faster in responding to a target face that followed an approach sequence, compared to both receding and static primes. In a second series of experiments, we investigated long-term effects of motion using a delayed visual search paradigm. After studying moving or static avatars, observers searched for target faces in static arrays of varying set sizes. Again, observers were faster at responding to faces that had been learned in the context of an approach sequence. Together these results suggest that the context of a moving body influences face processing, and support the hypothesis that our visual system has mechanisms that aid the encoding of behaviourally-relevant and familiar dynamic events.     

Anticipating intentional actions: The effect of eye gaze direction on the judgment of head rotation

Using a representational momentum paradigm, this study investigated the hypothesis that judgments of how far another agent’s head has rotated are influenced by the perceived gaze direction of the head. Participants observed a video-clip of a face rotating 60° towards them starting from the left or right profile view. The gaze direction of the face was either congruent with, ahead of, or lagging behind the angle of rotation. Following this, two static faces, at varying angles of rotation with respect to the end-point angle of the face in the video-clip, were presented simultaneously. The task of the participants was to decide which of the two heads was at an angle best resembling the angle of the end-point of the moving face. The critical test condition consisted of one test face oriented at 10° before, and the other at 10° after the end-point. The ‘lagging behind’ gaze condition elicited a significant underestimation of the rotation compared to the ‘congruent’ and ‘ahead’ gaze conditions. Participants did not exhibit similar biases when judging the rotation of several non-face control stimuli with visual features that mimicked different aspects of gaze direction. The findings suggest that when the gaze direction of a perceived agent is incongruent with the direction of the agent’s head motion observers automatically utilise this discrepancy to adjust their inferences about the agent’s intended heading direction.     

儿童运动视觉表象操作水平的发展及影响因素

采用计算机软件控制实验,以暴露运动一段行程后进入遮蔽的光点为刺激物,光点以三种不同运动速度、三种不同运动行距组合呈现,要求儿童判断光点到达目标位置时按键反应。结果表明：5—19岁儿童运动视觉表象操作水平的发展存在5一8岁、11—14岁两个加速期;客体运动速度对运动视觉表象操作绩效有显著影响,5、8、11岁组快速较中速下．5．8岁组中速较慢速下操作准确性均有显著降低;客体运动行距对运动视觉表象操作绩效也有显著的影响．5、8、11岁组右目标位置下较中目标位置下操作准确性显著降低;性别对运动视觉表象操作水平无显著影响。