Motion prediction and the velocity effect in children

In coincidence‐timing studies, children have been shown to respond too early to slower stimuli and too late to faster stimuli. To examine this velocity effect, children aged 6, 7.5, 9, 10.5, and adults were tested with two different velocities in a prediction‐motion task which consisted of judging, after the occlusion of the final part of its path, the moment of arrival of a moving stimulus towards a specified position. A similar velocity effect, resulting in later responses for the faster velocities than for the slower, was found primarily in the three younger groups of children (for the longer occlusion conditions: 600–1,320 milliseconds). However, this effect was not seen in all children in these groups. Individual analyses showed that this velocity effect, when present, is linked to the use of distance rather than time information, or to the confusion between these in extrapolating the occluded trajectories. The tendency to use one type of information or the other is a good predictor of accuracy and variability in this task and a good indicator of the development stage of the participants. Across development, children tend to initially use distance information with poor accuracy but relative consistency in responses. In a second stage, they use time and distance information alternatively across trials trying to find a better source of information with still poor accuracy and now great variability. In a final stage, they use time information to reach consistency and accuracy in their responses. This chronology follows the stages proposed by Savelesbergh and Van der Kamp (2000) explaining development with an initial stage of ‘freezing’ non‐optimal relationships between information and movement, then a ‘freeing’ stage during which new solutions are searched for, and finally an ‘exploiting’ stage with an optimal relationship between information and movement.     

Are Reaching Movements Planned to be Straight and Invariant in the Extrinsic Space? Kinematic Comparison Between Compliant and Unconstrained Motions

Two main questions were addressed in the present study. First, does the existence of kinematic regularities in the extrinsic space represent a general rule? Second, can the existence of extrinsic regularities be related to specific experimental situations implying, for instance, the generation of compliant motion (i.e. a motion constrained by external contact)? To address these two questions we studied the spatio-temporal characteristics of unconstrained and compliant movements. Five major differences were observed between these two types of movement: (1) the movement latency and movement duration were significantly longer in the compliant than in the unconstrained condition; (2) whereas the hand path was curved and variable according to movement direction for the unconstrained movements, it was straight and invariant for the compliant movements; (3) whereas the movement end-point distribution was roughly circular for the unconstrained movements, it was consistently elongated and typically oriented in the movement direction for the compliant movements; (4) whereas constant errors varied as a function of target eccentricity for the unconstrained movements, they were independent of this factor for the compliant movements; (5) the instruction to move the final effector along a straight line path influenced the characteristics of the unconstrained movements but not the characteristics of the compliant movements. When considered together, the previous observations suggest that compliant and unconstrained movements involve different planning strategies. Our data support the hypothesis that unconstrained motions, unlike compliant motions, are not programmed to follow a straight line path in the extrinsic space. This observation provides a theoretical frame of reference within which some apparently contradictory results reported in the movement generation literature may be explained.     

Differences in performance of young and old monkeys on a visuospatial memory task

Two groups of stumptailed macaques (Macaca arctoides) were compared in terms of performance on a visuospatial working memory task involving repeated presentations of an array of 15 doors, each of which concealed one food reward at the start of a session. Rewards obtained by the subject were not replaced. Errors were defined as responses to doors previously pushed open during the session. Both groups generally obtained all rewards and showed improved performance across sessions, but old monkeys consistently made more errors than young ones, especially in the latter half of a given session. Further, old monkeys were less diverse in the errors they made, indicating different response strategies by the two groups.     

Some introductory thoughts

Education must be a central part of the building of Europe: because access to knowledge can overcome the dangers of exclusion, but also because education offers the key to citizenship and thereby to the future of Europe.