Prehension in children and adults: The effects of object size

Studies of visually goal-directed arm movements in adults have shown that various task constraints such as intention, context, and object properties affect different kinematic characteristics of the movement components (Jeannerod, 1984; MacKenzie et al., 1987; Marteniuk et al., 1987, 1990; Paulignan et al., 1991; Soechting, 1984). The purpose of the present study was to compare the effects of varying object size on the kinematics of reaching and grasping in both children and adults. Five children aged 9–10 years and five adults aged 18–24 years reached for and grasped three different sized cubes. Results revealed that object size had the same effect on the planning and control of reaching and grasping movements in children as in adults. Unlike adults, however, children in this age range spent more time in deceleration and reached peak aperture much later in the movement trajectory. The results were interpreted as immature integration of the visual and proprioceptive systems in 9–10 year olds. The implications of these findings for further examining developmental trends in prehension are discussed.PsycINFO classification: 2330     

The Effects of Object Weight on the Kinematics of Prehension

The purpose of these experiments was to determine the effects of object weight and condition of weight presentation on the kinematics of human prehension. Subjects performed reaching and grasping movements to metal dowels whose visible characteristics were similar but whose weight varied (20, 55, 150, 410 g). Movements were performed under two conditions of weight presentation, random (weight unknown) and blocked (weight known). Three-dimensional movements of the thumb, index finger, and wrist were recorded, using a WATSMART system to obtain information regarding the grasp and transport components. The results of the first experiment indicated that object weight and condition of presentation affected the temporal and kinematic measures for both the grasp and transport components. In conjunction with the results of a second experiment, in which time in contact with the dowel was measured, it was shown that the free-motion phase of prehension (i.e., up to object contact) was invariant over the different conditions, however. The changes were observed in the finger-object interaction phase (when subjects applied forces after contact with the dowel), prior to lift-off. These results were interpreted as indicating (a) object weight does not influence the planning and execution of the free-motion phase of prehension and (b) there are at least two motor control phases involved in prehension, one for making contact with the object and the other for finger-object interaction. The changing contributions of visual, kinesthetic, and haptic information during these two phases is discussed.     

Prehension in young children with Down syndrome

Prehension was examined in 3-year old children with Down syndrome (DS, n = 3) and in typically-developing children matched in chronological age (3-year olds; n = 3) or mental age and motor experience (2-year olds; n = 3). The task required reaching to grasp dowels. Video-based movement analysis yielded temporal and kinematic measures. Children with DS were hypothesized to have deficits in feedback-dependent components of prehension (anticipatory grip-closure and deceleration of reach), whereas feedforward components (reach's acceleration phase; grasp's preshaping) were assumed to be unimpaired [Latash, 1993, Control of human movement, pp. 283-292; Latash, 1994, What is clumsiness? In: Motor Control and Down Syndrome II Proceedings of the second international conference, pp. 68-71]. The findings supported these hypotheses. In comparison to control groups, children with DS had significantly: (a) less time in deceleration of reaching, (b) fewer anticipatory grip-closures, and (c) longer movement times for dowel-lift. Young children with DS appeared to use dowel-contact to decelerate the limb and initiate grip-closure. In contrast, reach-acceleration time and grasp-preshaping did not differ across groups. These findings suggest that children with DS display qualitative differences in motor capabilities rather than simply a delayed rate of typical developmental progression.     

Adjustments to Local Friction in Multifinger Prehension

The authors studied the effects of surface friction at the digit-object interface on digit forces and moments when 12 participants statically held an object in a 5-digit grasp. The authors changed low-friction contact (LFC) with rayon and high-friction contact (HFC) with sandpaper independently for each digit in all 32 possible combinations. Normal forces of the thumb and virtual finger (VF), an imagined finger with a mechanical effect equal to that of the 4 fingers, increased with the thumb at LFC or with an increase in the number of fingers at LFC. When the thumb was at LFC, the thumb tangential force decreased. The VF tangential force decreased when the number of fingers at LFC increased. The interaction of the local responses to friction and the synergic responses necessary to maintain the equilibrium explain the coordination of individual digit forces.     

Prehension and perception of size in left visual neglect

Right hemisphere damaged patients with and without left visual neglect, and age-matched controls had objects of various sizes presented within left or right body hemispace. Subjects were asked to estimate the objects' sizes or to reach out and grasp them, in order to assess visual size processing in perceptual-experiential and action-based contexts respectively. No impairments of size processing were detected in the prehension performance of the neglect patients but a generalised slowing of movement was observed, associated with an extended deceleration phase. Additionally both patient groups reached maximum grip aperture relatively later in the movement than did controls. For the estimation task it was predicted that the left visual neglect group would systematically underestimate the sizes of objects presented within left hemispace but no such abnormalities were observed. Possible reasons for this unexpected null finding are discussed.     

Achieving Coordination in Prehension: Joint Freezing and Postural Contributions

The focus of the present study was on the intersegmental relationships that emerge when both task and oganismic constraints are imposed upon the coordination system. Seven right-handed subjects were required to reach and grasp a cup (hand transport phase) and place it on a designated target (cup transport phase), using either their preferred or nonpreferred hand. The kinematics of the movement were examined as a function of task (grasping a full cup versus grasping an empty one) and organismic (preferred or nonpreferred hand) constraints. During the hand transport phase, a task constraint effect was revealed through an increase in the low-velocity phase for the full cup condition. This constraint coexisted with a decrease in angular motion of the shoulder and elbow joints, indicating subjects reduced the number of variables to be independently controlled in the final homing-in stage of the movement. Accompanying this decrease in angular change was an increase in the displacement of the trunk. During the cup transport phase, the trunk was shown to contribute significantly more to the movement in the full cup condition and for the left hand movements, thereby increasing the stability of the movement system. These findings are in agreement with Bernstein's (1967) notion of fixating parts of the body as an initial solution to a movement problem, and they lend support to the concept of a proximodistal organization of coordination.     

The Tasks and Traps of Relationships

SUMMARY

This article approaches relationships from primarily a systemic-psychodynamic framework in that psychoanalytic interpretations and assumptions are integrated into a basic systemic orientation The paper focuses on the prerelationship developmental tasks, relationship developmental tasks, the role of love and intimacy in emotional maturity, and the traps and pitfalls commonly encountered by couples, as illustrated by the activation of protective, defensive mechanisms. The material is illustrated by a case presentation. Implications for counseling are considered throughout.     

Effects of Object Texture on Precontact Movement Time in Human Prehension

Using kinematic data in a precision-grip reaching task, Weir, MacKenzie, Marteniuk, and Cargoe (1991) concluded that prior to contact with an object, its texture does not affect the course of grasping. The present study used their task of reaching for and lifting a slippery-, normal- (polished metal), or rough-surfaced dowel. This occurred under the original, blocked condition, in which textures were held constant within a series of trials, and under a new, randomized condition, in which textures varied randomly from trial to trial. Performance was also examined over more extended periods of practice. Reaction time and precontact movement time were directly measured. In contrast to the results of Weir et al., 1991, reaching for the slippery dowel resulted in slower movement time. This effect was found both early and late in practice for the randomized condition; it was found only in late practice for the blocked condition. These effects can be attributed to the greater geometric and dynamic precision required for lifting a slippery object.     

Organisation and Recall in Verbal Tasks and in Subject-performed Tasks

In memory for subject-performed tasks (SPTs), subjects encode a list of simple action phrases (e.g. "lift the pen", "open the book") by performing these actions during learning. Performing tasks has proved to be a much more efficient type of encoding than verbal tasks (VTs), in which subjects only listen to the action phrases in order to memorise them. It is assumed that good item-specific encoding after SPTs plays an important role in the SPT effect. The role of relational encoding for the SPT effect is less clear, as is the question of whether SPT encoding is automatic or controlled. Two experiments were conducted to address these issues. Subjects learned lists which were categorically structured in VTs and SPTs, under focal attention or divided attention. The results indicated that relational encoding does not differ between VTs and SPTs, and that free recall is impaired in both cases by divided attention, more so in VTs than in SPTs. It is concluded that the SPT effect is primarily based on item-specific information rather than on relational information, and that VTs are more dependent than SPTs on active encoding.     

A Method for Identifying the Initiation of Reaching Movements in Natural Prehension

Identifying the start of a movement is critical for calculating variables such as movement duration, movement speed, or trajectory length and straightness. In most experiments, the problem is simplified by giving instructions to the subjects and by constraining the task. This is not possible in populations that are too young or disabled to understand and execute the task as instructed. In this article, a method is presented for reliably identifying the onset of reaches in infants, whose movements are embedded in their ongoing activities. A computer program prompts the user to choose reach initiation on the basis of comparison between hand kinematics and videotaped behavior and to code the reach as emerging from 1 of 4 movement contexts. The method is highly reliable in infants of all ages and captures expected age-related changes in reaching. It is suggested that researchers could use this or a similar method to study movements that are part of natural, ongoing activities in normal and in clinical populations     

儿童在错误信念任务上的知识偏差

采用3种任务考查儿童在错误信念（FB）推理中是否存在知识偏差。被试为60名3—5岁幼儿,结果表明,对于3岁及4岁儿童来说,FB任务是存在知识偏差的。知识偏差的大小与年龄呈负相关关系,3岁与4岁、4岁与5岁儿童的知识偏差的大小均有显著差异。     

Accommodating Surprise in Taxonomic Tasks: The Role of Expertise

This paper reports a psychological study of human categorization that looked at the procedures used by expert scientists when dealing with puzzling items. Five professional botanists were asked to specify a category from a set of positive and negative instances. The target category in the study was defined by a feature that was unusual, hence situations of uncertainty and puzzlement were generated. Subjects were asked to think aloud while solving the tasks, and their verbal reports were analyzed. A number of problem solving strategies were identified, and subsequently integrated in a model of knowledge‐guided inductive categorization. Our model proposes that expert knowledge influences the subjects' reasoning in more complex ways than suggested by earlier investigations of scientific reasoning. As in previous studies, domain knowledge influenced our subjects' hypothesis generation and testing; but, additionally, it played a central role when subjects revised their hypotheses.     

The Naive Topology of the Conscious Subject

What does our naïve conception of a conscious subject demand of the nature of conscious beings? In a series of recent papers David Barnett has argued that a range of powerful intuitions in the philosophy of mind are best explained by the hypothesis that our naïve conception imposes a requirement of mereological simplicity on the nature of conscious beings. It is argued here that there is a much more plausible explanation of the intuitions in question. Our naïve conception of a conscious subject imposes a requirement of topological integrity.     

Trunk-Assisted Prehension: Specification of Body Segments With Imposed Temporal Constraints

The authors used a trunk-assisted prehension task to examine intersegment coordination. Participants (N = 7) reached to grasp an object placed beyond full arm extension, thus requiring trunk flexion to achieve the target object, under 4 varying temporal constraints. Kinematic analyses were performed in which the motions of the arm, the trunk, and the endpoint were characterized. The spatial trajectories and the segments' peak velocity data revealed that under high temporal constraints the arm was more responsible for endpoint motion than the trunk, whereas in the unconstrained condition the trunk was more involved. In addition, the arm exhibited a decline in spatial variability toward the end of the movement in all conditions, whereas the trunk did not. The present study is the first to show that when temporal demand is increased for a trunk-assisted prehensile task, the arm plays a larger role than the trunk in the transport of the hand to the object The data also suggest that the arm participates in the fine accuracy control of the reach, whereas the trunk does not.     

汉语阅读发展研究中几种实验任务之间关系的探讨

本研究综合考察汉语阅读获得与发展研究中经常使用的注音、命名与组词,听写与多重选择的关系。结果发现：注音与命名有很强的一致性,并且都与组词有很高的棚关;在这些任务中,听写的难度最大,多重选择最易;几种任务存在共同的加工规律。文章从词汇识别过程讨论了这些结果的理论含义。     

Deceleration requirements and the control of pointing movements

When a limb is moved from one position to a target object, the limb and the target frequently collide. Often, the goal of the movement is to strike the target with a particular magnitude of impact. For single-aiming movements, impact forces have been shown to increase systematically with both an increased movement amplitude and a decreased movement time, thus providing deceleration to the moving limb. Models of speed-accuracy trade-off, however, have neglected to account for the contribution of these impact forces in the control of accurate movements. The aim of this experiment was to examine the modifications in the control strategy as a function of the amount of impact force a subject is allowed to use in decelerating his or her limb. Results showed that the structure of the acceleration-time functions was dictated by the amount of impact force subjects were allowed to use in decelerating the limb. Movement endpoint variability decreased as more impact force was used. The experiment suggests that the impact with a target is an important contributor to the deceleration of the moving limb and a critical determinant of movement organization.     

颜色特征加工任务间的注意瞬脱研究

本研究以两个实验对颜色特征加工任务间的注意瞬脱效应进行探讨。实验一要求被试对首先呈现的两个色块(记忆项)与随后呈现的两个色块(检测项)是否相同进行比较。结果发现,在记忆项与检测项的SOA为220ms的条件下,记忆项加工对认知资源的持续占用使检测项的加工绩效下降。实验二含两个需相继执行的任务(T1和T2),二者均为比较同时呈现在屏幕左右两侧的两色块颜色是否相同。结果发现,对颜色特征的觉察即可产生注意瞬脱效应,其大小及时程与经典的采用字母识别任务的研究获得的注意瞬脱效应相当。上述结果表明,特征搜索的完成需有限认知资源的参与。然而,注意瞬脱过程中,特征加工与需对知觉对象细节信息进行提取的辨别任务(如字母辨别任务)在消耗认知资源的量上并无差别。     

Representations in Distributed Cognitive Tasks

In this article we propose a theoretical framework of distributed representations and a methodology of representational analysis for the study of distributed cognitive tasks—tasks that require the processing of information distributed across the internal mind and the external environment. The basic principle of distributed representations Is that the representational system of a distributed cognitive task is a set of internal and external representations, which together represent the abstract structure of the task. The basic strategy of representational analysis is to decompose the representation of a hierarchical task into its component levels so that the representational properties at each level can be independently examined. The theoretical framework and the methodology are used to analyze the hierarchical structure of the Tower of Hanoi problem. Based on this analysis, four experiments are designed to examine the representational properties of the Tower of Hanoi. Finally, the nature of external representations is discussed.     

The Acceptability and Representativeness of Standardized Parent-Child Interaction Tasks

Analogue behavioral observation of structured parent-child interactions has often been used to obtain a standardized, unbiased measure of child noncompliance and parenting behavior. However, for assessment information to be clinically relevant, it is essential that the behavior observed be similar to that which the child normally experiences and elicits. Furthermore, assessment procedures should be socially appropriate and acceptable to participants in order to facilitate investment in the assessment, and potentially treatment, process. Although analogue tasks have been shown to have reasonable psychometric properties, the social validity of these methods has not been evaluated. This study examined the acceptability and representativeness of 4 widely utilized, laboratory-based parent-child interaction tasks in a sample of 43 nonreferred, 3- to 6-year old children and their mothers, who were of European-American or African-American ethnicity. Mothers rated the acceptability of each task and the degree to which it was representative of “typical” interactions occurring with the child. Repeated-measures analyses of variance revealed high levels of acceptability and representativeness for all tasks, but consistent differences across tasks. These ratings were predominantly stable over a 2-week period. Additionally, social validity ratings were significantly associated with parenting self-esteem, maternal ethnicity, child gender, and child age, but not child behavior problems. Limitations and implications of these findings for the assessment of parent-child interaction are discussed.