The acquisition of catching under monocular and binocular conditions

The effects of binocular and monocular viewing on spatial and temporal errors in one-handed catching were investigated in two experiments. The first experiment-using expert catchers-recorded more spatial errors under the monocular than under the binocular condition. No significant differences in the number of temporal errors were apparent. In a second experiment, which paradigm, relatively poor catchers were trained under both vision conditions. Its objective was to investigate whether the superior results obtained under the binocular condition in the first experiment, for the number of catches and number of spatial errors, could be attributed simply to the fact that subjects had more experience with binocular than monocular viewing. The following results occurred after a period of training (a) a significant reduction in the number of spatial errors under the monocular condition, reaching a level similar to that under the binocular condition; (b) no significant reduction in the number of spatial errors when subjects transferred from monocular to binocular viewing, and significantly more spatial errors when subjects transferred from binocular to monocular viewing; and (c) a training-sequence effect. The latter effect indicates that subjects had more benefit from training in the sequence monocular-binocular than vice versa. These findings are discussed in the context of the strategies of specificity of learning and use of multisources.     

Influence of mechanical factors on movement units in infant reaching

In a number of studies it is assumed that movement units (combinations of an acceleration and a deceleration in the tangential velocity profile) are a reflection of the control process. In this study, we investigated to what extent movement units reflect the oscillatory mechanics of the arm. At the ages of 16 and 20 weeks, the age range in which infants just begin to reach, a toy rattle was presented in three conditions, with varying external forces acting on the arm: sitting, sitting with masses on the forearms, and supine.The tangential velocity profile of the wrist during successful reaching attempts was decomposed to a gravity-dependent (φ_v), and a gravity-independent component (φ_h), and movement units were determined in the total velocity profile and in its components. Significant effects of experimental condition, but not age, were found for movement time, number of movement units and duration ofphi;_hcomponent units. It was shown that these effects can be accounted for by a simple mechanical model, in which the arm is approximated as a harmonic oscillator governed by, gravity, the moment of inertia of the arm, and the stiffness of the shoulder joint. Stiffness values, derived from fitting the model to the data, were in the order of 1 Nm/rad.From these results we conclude that movement units in an infant's initial attempts at reaching are to a large extent a reflection of the mechanical context.     

The relation between infants' perception of catchableness and the control of catching

The authors studied how infants come to perceive and act adaptively by presenting 35 three- to nine-month-olds with balls that approached at various speeds according to a staircase procedure. They determined whether infants attempted to reach for the ball and whether they were successful (i.e., contacted the ball). In addition, the time and distance of the ball at the onset of the catching movements were measured for the successful interceptions. The authors found that not only catching skill but also the perceptual judgments of the catchableness improved with age; infants started to take their catching ability into account when judging whether a ball was catchable. Moreover, the authors observed that infants who made imprecise perceptual judgments were more likely to use a distance control strategy, whereas infants who made accurate perceptual judgments were more likely to use the more adaptive time strategy to control the catching movements. They conclude that the present study supports the proposal that, even in prelocomotor infants, the development of perception is intricately linked to or constrained by development in the visual control of action.     

Children's use of the bearing angle in interceptive actions

The authors investigated the effect of ball velocity and walking direction on children's adherence to the constant bearing angle (CBA) strategy. Children (N = 20) approached a moving ball to manually intercept it at a predefined target area. Results revealed that 10- to 12-year-olds adhered more than 5- to 7-year-olds to the CBA strategy. Younger children deviated more than older children from smaller angles of approach and lower ball velocities. The present findings suggest that younger children have difficulty adjusting to task requirements because they fail to couple walking velocity with ball velocity. The improvement seen with increasing age suggests that compliance with the CBA strategy may be attributed to older children's enhanced coincidence anticipation.     

Effects of experience on the coordination of internally and externally timed soccer kicks

The authors investigated differences in the soccer kick between 8 experienced and 10 less experienced participants in 2 different task conditions (kicking a stationary ball or a moving ball at a target). The experienced participants were more accurate than their less experienced counterparts, whereas there were no differences in maximum foot velocity between groups or between conditions. When compared with their performance in the stationary condition, participants kicked the moving ball with a smaller range of movement at the knee of the kicking leg, maintaining a proximodistal coordination pattern. Because of their significantly shorter knee-flexion phase, the participants in the experienced group displayed a significantly shorter time between initiation of the forward swing of the kick and ball contact than that of those in the less experienced group. The rapid knee flexion may have been a strategy of exploiting passive dynamics to increase accuracy rather than velocity. Members of both groups showed a proximodistal initiation sequence in the kicking leg, which suggests that players can acquire that coordination pattern with relatively little structured practice and that further practice leads to improvement possibly through the increased exploitation of passive dynamics.     

A Measure for the Reliability of a Rating Scale Based on Longitudinal Clinical Trial Data

A new measure for reliability of a rating scale is introduced, based on the classical definition of reliability, as the ratio of the true score variance and the total variance. Clinical trial data can be employed to estimate the reliability of the scale in use, whenever repeated measurements are taken. The reliability is estimated from the covariance parameters obtained from a linear mixed model. The method provides a single number to express the reliability of the scale, but allows for the study of the reliability’s time evolution. The method is illustrated using a case study in schizophrenia. The authors are grateful to J&J PRD for kind permission to use their data. We gratefully acknowledge support from the Belgian IUAP/PAI network “Statistical Techniques and Modeling for Complex Substantive Questions with Complex Data.”     

Selective attention to threat in the dot probe paradigm: differentiating vigilance and difficulty to disengage

The dot probe task [J Abnorm Psychol 95 (1986) 15] is an often-used paradigm to investigate selective attention to threat. A facilitated response to probes that appear at the same location of threat information in comparison with responses to probes at the opposite location of threat information is interpreted as vigilance for threat. We argue that the findings in the dot probe paradigm are ambiguous evidence for the vigilance to threat hypothesis. Results can also be interpreted as a difficulty to disengage from threat. In this study, 44 undergraduates performed a pictorial version of the probe detection task. Taking into account the reaction times on neutral trials, we found no evidence for a facilitated detection of threatening information. It was found that the dot probe effects are at least partially due to disengagement effects. The implications of these results for the understanding of attentional bias in normal and anxious individuals are discussed.