Attention Is Required to Coordinate Reaching and Postural Stability during Upper Limb Movements Generated While Standing

Abstract

In the present study we investigated how attention contributes to the interaction between reach planning and execution, and postural control. Reaching movements were generated while standing and were performed either in isolation or in conjunction with a secondary reaction time (RT) task. In addition, to better understand how online movement control is affected by this interaction, the reaching movements could be unexpectedly perturbed medial-laterally. Postural kinetic, arm kinematic and RT, and secondary RT measures were used to characterize the responses. Results indicate task performance worsened when both the reaching and secondary tasks were completed simultaneously. Our results imply the generation of reaching movements while standing requires attentional resources to properly coordinate the interaction between the reaching task and postural control.     

Head and Trunk Movements During Turning Gait in Children with Cerebral Palsy

Thirty children with cerebral palsy (CP) and 22 typical developing (TD) were tested with 3D-gait analysis. At turning, trunk rotation was larger in CP2 (GMFCS II) than in TD and CP1 (GMFCS I), and head flexion was larger in CP3 (GMFCS III) than TD. Maximum head and trunk flexion values during the entire trial were larger in CP3 than in the other groups, and trunk flexion was larger in CP2 than in TD. Trial time increased with GMFCS-level. Less trunk rotation than TD and CP1 reflects spatial insecurity in CP2, which in CP3 is compensated by the walker. The flexed head and trunk in CP3 and trunk in CP2 may reflect deficits in proprioception and sensation requiring visual control of the lower limbs.     

On Potential-Based and Direct Movements in Information Spaces

Learning can be portrayed as a movement in a state space. Potential-based explanations of such movements hold that learners use a gradient-descent process to minimize a potential function. Direct explanations hold that learning is specific to information for learning. This study contrasts specific hypotheses derived from these general approaches. Participants estimated the length of arrow shafts of Müller-Lyer displays. Experiment 1 shows that learning in this paradigm can indeed be portrayed as a movement in a state space. In Experiment 2 nonveridical feedback was used in such a way that the contrasted hypotheses predicted learning in opposite directions. No learning was observed. In Experiment 3, movements in the state space were observed with practice conditions in which one of the hypotheses specified a movement in the state space whereas the other did not specify any movement. A tentative explanation for these findings is that both hypotheses are partly correct. However, more than to the empirical findings for this particular task, the authors wish to draw attention to the distinction between potential-based and direct processes—a distinction that they consider of general importance for the understanding of learning.     

Head and Trunk Control While Walking in Older Adults with Diabetes: Effects of Balance Confidence

Investigations of gait in older adults with diabetes mellitus (DM) have been primarily focused on lower limb biomechanical parameters. Yet, the upper body accounts for two thirds of the body's mass, and head and trunk control are critical for balance. The authors examined head and trunk control during self-selected comfortable, fast, and dual-task walking and the relationship between balance confidence and potential head-trunk stiffening strategies in older adults with DM without diagnosed diabetic peripheral neuropathy (DPN). Twelve older adults with DM without diagnosed DPN (DM group) and 12 without DM (no-DM group) were recruited. Walking speed, peak-to-peak head and trunk roll displacement, head and trunk roll velocity, and head-trunk correlation were measured while walking at a self-selected comfortable or fastest possible speed with or without a secondary cognitive task. The Activities-specific Balance Confidence scale measured balance confidence. Subtle group differences in axial segmental control (lower trunk roll velocity; higher head-trunk correlation) were apparent in older adults with DM even in the absence of DPN. Balance confidence was 19% lower in the DM group than in the no-DM group, and partially explained (34%) the group difference in head-trunk stiffening. These results emphasize the need for proactive monitoring of postural control and balance confidence before the onset of DPN.     

The Clinical and Forensic Value of Information that Children Report While Drawing

Drawing is commonly used in clinical interviews to help children talk about their experiences. Research has shown that drawing increases the amount of information that children report about some emotional experiences. Here, we aimed to investigate the use of drawing in interviews about other, clinically relevant emotions, and the clinical and forensic relevance of the information that children report while drawing. To do this, sixty 5‐ to 6‐ and 11‐ to 12‐year‐olds drew and told, or told, about prior experiences that had made them feel happy, angry, proud (confident), and worried (nervous). For all emotions, drawing and telling increased the amount of forensically relevant, episodic details (e.g., who was there and what happened) that children reported relative to telling alone. In contrast, drawing and telling did not alter the amount of information that children reported about clinically relevant details (e.g., thoughts and emotions). We discuss the implications of these findings for using drawing in interviews with children. Copyright © 2013 John Wiley & Sons, Ltd.     

Early Development of Head Movements Between Birth and 4 Months of Age: A Longitudinal Study

The control of head posture and movement play a significant role in the early development of motor skills. However, a detailed kinematic study charting this development is currently lacking. Hence, the authors performed a longitudinal study of 18 infants between birth and 4 months charting changes in head posture and movements when tracking a visual object. The results showed that beyond 2 months, the head was more often held at the body midline and this was accompanied by an increase in the number, extent, and speed of head movement. Further, it was found that head movements were organized into movement units. Movement units initially increased in number, but after 3 months decreased in number and increased in duration, especially after peak velocity. This more symmetrical profile velocity points to more controlled head movements after 3 months of age.     

Eye Movements Indicate the Temporal Organisation of Information Processing in Graph Comprehension

Hierarchical graphs (e.g. file system browsers and preference trees) represent objects (e.g. files and folders) as graph nodes and relations between them (e.g. sub‐folder relations) as lines. We investigated the temporal organisation of two processes that are necessary for comprehending such graphs—search for the graph nodes and reasoning about their relation. We tracked eye movements to change graphs while participants interpreted them. In Experiment 1, we masked the graph at a time when search processes had finished but reasoning was hypothetically ongoing. We observed a dramatic deterioration in comprehension compared with unmasked graphs. In Experiment 2, we changed the relation between critical graph nodes after search for them had finished, unbeknownst to participants. Participants mostly based their response on the graph as presented after the change. These results suggest that comprehension processes are organised in a sequential manner, an observation that can potentially be applied to the interactive presentation of graphs. Copyright © 2014 John Wiley & Sons, Ltd.     

The Role of Oculomotor Information in the Learning of Sequential Aiming Movements

With their eyes initially on either the home, midline, or final end position, 30 participants practiced a 2-target aiming movement. After 120 acquisition trials, participants performed a retention test and were then transferred to each of the other 2 eye conditions. During acquisition, all groups improved over practice, but the home group showed the greatest improvement. The temporal improvement was most pronounced in the times spent after peak velocity. Retention and transfer tests indicated that participants performed best under eye-movement conditions that were the same as the 1 they had practiced in. There was also positive transfer of training between conditions in which the oculomotor information was similar. Thus, to optimize learning, one should practice under the same afferent and oculomotor conditions that will be required for the final performance.     

Television and Reality: Toddlers' Use of Visual Information from Video to Guide Behavior

Toddlers' ability to use a television display in order to guide their object retrieval and object placement was examined. In the first experiment, 2-, 2.5-, and 3-year-olds watched a toy being hidden in an adjacent room, after which they were asked to find it. In the second experiment, 2-year-olds watched a toy being placed in the adjacent room and were then asked to place the toy in the same place. Half the children in each experiment watched the event through a window and half watched the event on television. In both experiments children's performance was worse if they saw the event on television, although retrieval improved with age. In both experiments the 2-year-olds' performance in the television condition started above chance and then deteriorated over trials. These and other studies indicate that toddlers have considerable difficulty using a video image in order to guide behavior in a real setting. Three hypotheses that could account for these findings are discussed.     

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.     

Planning of Reach-and-Grasp Movements: Effects of Validity and Type of Object Information

Individuals are assumed to plan reach-and-grasp movements by using two separate processes. In 1 of the processes, extrinsic (direction, distance) object information is used in planning the movement of the arm that transports the hand to the target location (transport planning); whereas in the other, intrinsic (shape) object information is used in planning the preshaping of the hand and the grasping of the target object (manipulation planning) In 2 experiments, the authors used primes to provide information to participants (N = 5, Experiment 1; N = 6, Experiment 2) about extrinsic and intrinsic object properties. The validity of the prime information was systematically varied. The primes were succeeded by a cue, which always correctly identified the location and shape of the target object. Reaction times were recorded. Four models of transport and manipulation planning were tested. The only model that was consistent with the data was 1 in which arm transport and object manipulation planning were postulated to be independent processes that operate partially in parallel. The authors suggest that the processes involved in motor planning before execution are primarily concerned with the geometric aspects of the upcoming movement but not with the temporal details of its execution.     

Phasing and the Pickup of Optical Information in Cascade Juggling

Four experiments were conducted to examine the relationship between the phasing of hand movements and the pickup of optical information in cascade juggling. Three jugglers of intermediate skill juggled three balls while wearing liquid crystal (LC) glasses that opened and closed at preset intervals. The first experiment, in which the duration of the viewing window was gradually reduced to zero, revealed a preference for seeing the segment of the ball flight following the zenith in one subject; such a preference was hinted at in the other two subjects. The second experiment, in which the tachistoscopic rhythm of the glasses was perturbed, showed that, in the case of a stable phase lock, the phasing of the hand movements was adjusted to restore the visibility of the segment following the zenith when it was lost. The third experiment, however, revealed that, after practice, the jugglers did not become better attuned to the optical information contained in this segment. The fourth experiment, in which two jugglers per- formed a cascade together while viewing the ball flights intermittently, suggested that haptic information about the trajectories of the balls to be caught is not necessary for subsequent catching: Optical information picked up during brief intervals of viewing was sufficient to perform the task equally well as when they juggled alone (i.e., when haptic information about the throws was available). Although, admittedly, the results raised only a tip of the veil covering the perceptual basis of juggling, they testify to the potential power of the new technique that was used to let subjects themselves reveal what optical information is relevant for performance.     

Conditioning and the Coordination of Movements

(Krech, D., and Crutchfield, R. S. Theory and Problems of Social Psychology. New York: McGraw-Hill, 1948. Pp. 639.) Reviewed by Gwynne Nettler     

Capacity to Handle Unassimilable Material: Coping Strategies of Schizophrenics and Normals

With anxiety conceptualized as resulting from a backlog of unassimilable or incongruent material, two processes were postulated to reflect coping strategies, assimilation and accommodation. These were assessed by means of a “picture interpretation task.” The hypothesis that schizophrenics fail to cope with unassimilable material because they are unable to accommodate (the process of changing internal schemata) was supported. The second prediction that paranoids would increase assimilation while nonparanoids would suppress assimilation was not supported.     

Playing the Odds: A New Response to Lucretius's Symmetry Argument

Abstract: Most commentators have assumed that Lucretius's symmetry argument against the fear of death is flawed. There remains, however, dispute as to what the flaw is. After establishing what I understand the target of Lucretius's argument to be (a desire for a longer life as such), I argue for a novel interpretation of what the flaw is, namely, that extending one's life into the time before one was actually born would be an uncertain bet for one who wanted to extend his life, whereas extending one's life beyond the time one actually dies is a sure bet. This account of what the flaw is has the particular merit of relying only on simple concepts used in everyday reasoning and thus can explain why Lucretius's argument gains no traction even in the absence of sophisticated philosophical analysis.