Roles of Visual Information for Control of Reaching Movements in Children

Poststroke hemiparetic individuals (n = 9) and a control group (n = 9) completed a frequency-scaled circle-drawing task in unimanual and bimanual conditions. Measures of intralimb spatial and temporal task accuracy and interlimb coordination parameters were analyzed. Significant reductions in task performance were seen in both limbs of the patients and controls with the introduction of bimanual movement. Spatial performance parameters suggested that the 2 groups focused on different hands during bimanual conditions. In the controls, interlimb coordination variables indicated predictable hand dominance effects, whereas in the patient group, dominance was influenced by the side of impairment and prior handedness of the individual. Therefore, in this particular bimanual task, performance improvements in the hemiplegic side could not be elicited. Intrinsic coupling asymmetries between the hands can be altered by unilateral motor deficits.     

Roles of Visual Information for Control of Reaching Movements in Children

What visual information do children normally require for the control of reaching movements? How is performance affected when children do not have access to the preferred mode of perceptual information? These questions were studied in 28 children who were tested on 3 occasions: at 6, 7, and 8 years of age. The task was to pick beads, 1 at a time, from 1 cup and carry them to another cup. With the aid of a mirror arrangement and a curtain, the amount of visual information was manipulated with regard to both the target and the performing hand. The movements were monitored with an optoelectronic device (SELSPOT II) and analyzed in terms of transport and object-handling phases. Results showed that object handling required visual information on both hand and target. For the transport phase of the movement, visual information on the spatial location of the target was sufficient, and sight of the hand did not improve performance. In contrast to adult subjects, when children did not have access to the required visual information, their performances deteriorated markedly. These results indicate that from the age of 6, children use visual information for control of arm movements in a manner like that of adults, although with less accuracy and speed. However, even 8-year-old children are limited in their ability to use alternative perceptual strategies for movement control, and they therefore become less flexible and more dependent on visual information.     

Determinants of Offline Processing of Visual Information for the Control of Reaching Movements

The authors investigated the use of visual feedback as a form of knowledge of results (KR) for the control of rapid (200-250 ms) reaching movements in 40 participants. They compared endpoint accuracy and intraindividual variability of a full-vision group (FV) with those of no-vision groups provided with KR regarding (a) the endpoint in numerical form, (b) the endpoint in visual form, or (c) the endpoint and the trajectory in visual form (DEL). The FV group was more accurate and less variable than were the no-vision groups, and the analysis of limb trajectory variability indicated that their superior performance resulted primarily from better movement planning rather than from online visual processes. The FV group outperformed the DEL group even though both groups were obtaining the same amount of spatial visual information from every movement. That finding suggests that the effectiveness with which visual feedback is processed offline is not a simple function of the amount of visual information available, but depends on how that information is presented.     

Visual Information and the Control of Reaching in Children: A Comparison Between Children With and Without Developmental Coordination Disorder

Three experiments were performed on reach and grasp in 9- to 10-year-old children (8 controls and 8 with developmental coordination disorder [DCD]). In normal reaching, children in the DCD group were less responsive to the accuracy demands of the task in controlling the transport component of prehension and spent less time in the deceleration phase of hand transport. When vision was removed as movement began, children in the control group spent more time decelerating and reached peak aperture earlier. Children in the DCD group did not do that, although, like the control group, they did increase grip aperture in the dark. When depth cues were reduced and only the target or only the target and hand were visible, children in the control group used target information to maintain the same grip aperture in all conditions, but DCD children behaved as if the target was not visible. Throughout the studies, the control group of 9- to 10-year-olds did not produce adult-like adaptations to reduced vision, suggesting that they had not yet attained adult-like integration of sensory input. Compared with control children, children with DCD did not exhibit increased dependence on vision but showed less recognition of accuracy demands, less adaptation to the removal of vision, and less use of minimal visual information when it was available.     

视觉客体在工作记忆中的累积构建

本研究采用变化觉察范式,以包含高、低空间频率信息的形状为刺激材料,探讨客体表征在工作记忆中的构建。结果发现,低频形状的工作记忆绩效显著优于高频形状,且二者辨别力的差别随SOA延长逐渐消失,说明低频信息优先进入视觉工作记忆。该结果支持工作记忆中客体表征的构建并非采用"全或无"的方式,而可能采用累积加工方式的假设。     

Control of Trajectory Modifications in Target-Directed Reaching

Human reaching movements to fixed and displaced visual targets were recorded and compared with simulated movements generated by using a two-joint arm model based on the equilibrium-point (EP) hypothesis (λ model) of motor control (Feldman, 1986). The aim was to investigate the form of central control signals underlying these movements. According to this hypothesis, movements result from changes in control variables that shift the equilibrium position (EP) of the arm. At any time, muscle activations and forces will depend on the difference between the arm's EP and its actual position and on the limb's velocity. In this article, we suggest that the direction of EP shift in reaching is specified at the hand level, whereas the rate of EP shift may be specified at the hand or joint level. A common mechanism underlying reaching to fixed and displaced targets is proposed whereby the EP of the hand shifts in a straight line toward the present target. After the target is displaced, the direction of the hand EP shift is modified toward the second target. The results suggest that the rate of shift of the hand EP may be modified for movements in different parts of the work space. The model, with control signals that vary in a simple fashion over time, is able to generate the kinematic patterns observed empirically.     

Object Recognition Difficulty in Visual Apperceptive Agnosia

Two patients with visual apperceptive agnosia were examined on tasks assessing the appreciation of visual material. Elementary visual functioning was relatively preserved, but they had profound difficulty recognizing and naming line drawings. More detailed evaluation revealed accurate recognition of regular geometric shapes and colors, but performance deteriorated when the shapes were made more complex visually, when multiple-choice arrays contained larger numbers of simple targets and foils, and when a mental manipulation such as a rotation was required. The recognition of letters and words was similarly compromised. Naming, recognition, and anomaly judgments of colored pictures and real objects were more accurate than similar decisions involving black-and-white line drawings. Visual imagery for shapes, letters, and objects appeared to be more accurate than visual perception of the same materials. We hypothesize that object recognition difficulty in visual apperceptive agnosia is due to two related factors: the impaired appreciation of the visual perceptual features that constitute objects, and a limitation in the cognitive resources that are available for processing demanding material within the visual modality.     

Control of Trajectory Modifications in Target-Directed Reaching

Human reaching movements to fixed and displaced visual targets were recorded and compared with simulated movements generated by using a two-joint arm model based on the equilibrium-point (EP) hypothesis (lambda model) of motor control (Feldman, 1986). The aim was to investigate the form of central control signals underlying these movements. According to this hypothesis, movements result from changes in control variables that shift the equilibrium position (EP) of the arm. At any time, muscle activations and forces will depend on the difference between the arm's EP and its actual position and on the limb's velocity. In this article, we suggest that the direction of EP shift in reaching is specified at the hand level, whereas the rate of EP shift may be specified at the hand or joint level. A common mechanism underlying reaching to fixed and displaced targets is proposed whereby the EP of the hand shifts in a straight line toward the present target. After the target is displaced, the direction of the hand EP shift is modified toward the second target. The results suggest that the rate of shift of the hand EP may be modified for movements in different parts of the work space. The model, with control signals that vary in a simple fashion over time, is able to generate the kinematic patterns observed empirically.     

Shape Integration for Visual Object Recognition and Its Implication in Category-Specific Visual Agnosia

A series of experiments was conducted on a patient (ELM) with bilateral inferior temporal lobe damage and category-specific visual agnosia in order to specify the nature of his functional impairment. In Experiment 1, ELM performed a task of picture/word matching that used line drawings of fruits and vegetables as stimuli. The pattern of confusions exhibited by the patient suggested a failure in processing the full range of shape features necessary for the unique specification of the target relative to other structurally related items. This hypothesis of a shape integration impairment was tested and verified by subsequent visual recognition experiments (Experiments 2-4), which used synthetic stimuli with shapes precisely defined on the dimensions of elongation, curvature, and tapering. Furthermore, it was determined (Experiment 5) that the integration deficit is specific to the retrieval of shape knowledge from memory and does not affect the encoding of the properties of visual stimuli. It is argued that these findings have critical implications for cognitive theories of visual object recognition and for an interpretation of the visual function of the inferior temporal cortex. Finally, it was shown that the patient's deficit for structural knowledge integration is modulated by the semantic properties of the objects (Experiment 6), thereby demonstrating the applicability of the present findings to an explanation of category-specific visual agnosia.     

Afferent Information for Motor Control: The Role of Visual Information in Different Portions of the Movement

The question addressed in the present study was whether subjects (N = 24) can use visual information about their hand, in the first half of an aiming movement, to ensure optimal directional accuracy of their aiming movements. Four groups of subjects practiced an aiming task in either a complete vision condition, a no-vision condition, or in a condition in which their hand was visible for the first half [initial vision condition (IV)] or the second half of the movement [final vision condition (FV)]. Following 240 trials of acquisition, all subjects were submitted to a transfer test that consisted of 40 trials performed in a no-vision condition. The results indicated that seeing the hand early in movement did not help subjects to optimize either directional or amplitude accuracy. On the other hand, when subjects viewed their hand closer to the target, movements resulted that were as accurate as those performed under a complete vision condition. In transfer, withdrawing vision did not cause any increase in aiming error for the IV or the no-vision conditions. These results replicated those of Carlton (1981) and extended those of Bard and colleagues (Bard, Hay, & Fleury, 1985) in that they indicated that the kinetic visual channel hypothesized by Paillard (1980; Paillard & Amblard, 1985) appeared to be inoperative beyond 40deg of visual angle.     

Object Size as a Determinant of Grasping in Infancy

The early development and patterns of development of prehensile ability were examined. Infants 5, 7, and 9 months old were presented five objects, 0.5, 1.0, 3.5, 7.0, and 14.0 cm in diameter. The findings revealed that infants as young as 5 months old were able to differentiate grip configurations as a function of object size. The number of grasps involving the two or three most radial digits (thumb, index finger, and long finger) increased greatly over this age span. At 9 months of age these kinds of grasps were 10 times more frequent than at 5 months of age. However, at each age level, when only the two or three most radial digits were used, the reaches were typically directed at the two smallest objects. These findings suggest that it was not a perceptual problem that the younger infants were facing, nor was the problem knowing when to use different kinds of grasps; rather, the problem was one of cortico-motoneural connections, which are better established in older infants. The findings also suggest that traditionally described sequential development of infants' prehension is rigid and conservative. The discrepancy with earlier results may also be attributed to the difference in the objects' sizes and the way they were presented.     

客体位置判断的视触关联研究

本文从个体对客体位置信息的加工出发,对触动觉位置判断以及视触位置信息整合的特点进行了探讨.两个实验分别从触动觉客体位置判断和视触位置判断及视触位置信息整合进行了研究.结果表明,当个体伸手对客体位置进行判断时,对对侧空间客体位置的变化感知更加敏感和准确,同时对距离呈现中心较远的客体的位置判断成绩较好,而客体呈现时所在的半空间对左右手的客体位置判断成绩并没有产生一致的影响;在视触空间位置信息整合时,随着空间信息加工任务难度的增大,个体通过手、胳膊的关节以及本体感觉所获得的对空间位置信息的表征的准确度可能会下降,而视觉对触动觉的引导作用开始显现出来并变得比较重要.     

客体替代掩蔽:视觉后向掩蔽研究的新进展

传统的知觉实验通常采用视觉后向掩蔽在网膜水平上干扰对目标刺激的加工,主要有模式掩蔽和偏对比掩蔽两种形式.近年来客体替代掩蔽(简称OSM)的实验研究表明,围绕目标刺激呈现四个点也可导致目标刺激的可见性下降.OSM发生在客体表征水平上,它既是值得研究的掩蔽现象,也可以作为一种新的研究范式.本文介绍OSM的心理物理学和计算模型研究,并指出它对于认知科学的重要意义.     

客体复杂度影响工作记忆可存储的客体数目

采用变化觉察范式,以对侧延迟活动（contralateral delay activity,CDA）的幅值为指标,通过操纵记忆刺激的复杂程度,对视觉工作记忆中可存储的客体数目（即工作记忆容量）问题进行了探讨。结果表明,2个复杂客体条件下的CDA幅值与4个复杂客体条件无显著差异,而4个简单客体条件的CDA幅值显著高于2个简单客体条件,即CDA的幅值受客体复杂度的调节。基于该结果推论：并非视觉工作记忆总能存储4个客体,其可存储的客体数目受客体复杂度影响。     

Addictions and the Quest to Control the Object

Most patients come into psychoanalytic treatment engaged in some form of repetitive, destructive behavior that is an externalization or projection of their internal struggles. One form of this object relational acting-out is the addictions, be they to alcohol, gambling, drugs, sex, procrastination, or other variations. The patient's experience is a "must do-can't stop" one that leaves them both desperate and relieved. Patients come to us wanting help in refraining from these addictive patterns. Sometimes, they are attending a 12-step program or are in a day treatment recovery program but need additional assistance in remaining free from their addictive behaviors. Others seek out psychoanalytic treatment while still involved in their addiction, but wish to stop the behavior and build a more positive plan for their lives. This paper examines the deeper object relational issues that lie behind the addictive process. The transference is often colored by acting-out, by sadomasochistic dynamics, by projective identification, and by fantasies of persecution and loss. Case material is used to explore these specific problems as well as the patient's general difficulties with paranoid-schizoid and depressive functioning.     

客体的视觉工作记忆研究进展

近年来,客体信息的视觉工作记忆问题引发了大量研究,并获得不少成果。本文对视觉工作记忆的研究范式,客体在视觉工作记忆中的存储方式、容量及保持时间等相关研究进行了概述,重点介绍关于视觉工作记忆存储单元和容量问题的"强客体"假设、"弱客体"假设和双重存储机制假设,并提出进一步的研究思路。     

Evidence Supporting the Importance of Peripheral Visual Information for the Directional Control of Aiming Movement

The focus of the present study was on determining whether the high level of directional accuracy found in aiming studies in which the subjects can see their hand in the visual periphery supports the existence of a kinetic visual channel or, rather, the advantage of binocular over monocular vision for movement directional control. The limits of this kinetic visual channel were also explored. The results of the 1st experiment indicated that seeing one's hand in the visual periphery is sufficient to ensure optimal directional aiming accuracy. Further, no differences in aiming accuracy were noted between monocular and binocular vision. These results supported the existence of a visual kinetic channel. In the 2nd experiment, whether this kinetic visual channel would operate with movements slower (55 degrees /s) than those usually used in studies that had proved its existence (over 110 degrees /s) was delineated. The results indicated that this visual kinetic channel was operative even at relatively slow movement velocities. Central vision of the hand seemed to be used for on-line directional control of relatively slow movements.     

Evidence Supporting the Importance of Peripheral Visual Information for the Directional Control of Aiming Movement

The focus of the present study was on determining whether the high level of directional accuracy found in aiming studies in which the subjects can see their hand in the visual periphery supports the existence of a kinetic visual channel or, rather, the advantage of binocular over monocular vision for movement directional control. The limits of this kinetic visual channel were also explored. The results of the 1st experiment indicated that seeing one's hand in the visual periphery is sufficient to ensure optimal directional aiming accuracy. Further, no differences in aiming accuracy were noted between monocular and binocular vision. These results supported the existence of a visual kinetic channel. In the 2nd experiment, whether this kinetic visual channel would operate with movements slower (55°/s) than those usually used in studies that had proved its existence (over 110°/s) was determined. The results indicated that this visual kinetic channel was operative even at relatively slow movement velocities. Central vision of the hand seemed to be used for on-line directional control of relatively slow movements.     

Control of Integrated Task Sequences Shapes Components of Reaching

Reaching toward an object usually consists of a sequence of elemental actions. Using a reaching task sequence, the authors investigated how task elements of that sequence affected feedforward and feedback components of the reaching phase of the movement. Nine right-handed adults performed, with their dominant and nondominant hands, 4 tasks of different complexities: a simple reaching task; a reach-to-grasp task; a reach-to-grasp and lift object task; and a reach-to-grasp, lift, and place object task. Results showed that in the reach-to-grasp and lift object task more time was allocated to the feedforward component of the reach phase, while latency between the task elements decreased. We also found between-hand differences, supporting previous findings of increased efficiency of processing planning-related information in the preferred hand. The presence of task-related modifications supports the concept of contextual effects when planning a movement.