Visual monitoring of goal-directed aiming movements.

Goal-directed movements are subject to intrinsic planning and execution variability, which requires that the central nervous system closely monitor our movements to ensure endpoint accuracy. In the present study, we sought to determine how closely the visual system monitored goal-directed aiming movements. We used a cursor-jump paradigm in which a cursor was unexpectedly translated soon after movement initiation. Some of the trials included a second cursor jump, and the cursor remained visible for different durations. The results indicate that seeing the cursor for only 16 ms after the second cursor jump was sufficient to influence the movement endpoint, which suggests that the visual system continuously monitored goal-directed movements. The results also suggest that the perceived position/trajectory of the effector was likely to have been averaged over a period of approximately 70 ms.

Automatic movement error detection and correction processes in reaching movements.

Manual aiming movements can be amended during their execution. Recent evidence suggests that error detection and correction are based on automatic and even reflexive processing of afferent information. In this study, we wanted to determine whether these processes are affected by the occurrence of successive events requiring adjustments of the originally planned movement. To reach our goal, we used a video-aiming task. For a small proportion of the trials, the cursor moved by the participant was translated laterally by 15 mm (cursor jump) soon after movement initiation. For some of the cursor-jump trials, a second cursor jump occurred 100 ms after the first one and canceled or doubled the initial cursor translation. Results showed that participants were able to cancel or double the size of the correction in response to the second cursor jump. More importantly, in double-jump trials, the correction latency for the first and second cursor jumps did not differ from that of single-jump trials. Moreover, the correction for the second cursor jump blended seamlessly with the correction for the first cursor jump. These observations suggest that the processes leading of a correction for a cursor jump do not interfere with incoming visual information.

Automaticity of online control processes in manual aiming.

Experiments that manipulated the visual feedback of the moving limb have suggested the existence of efficient and automatic online correction processes. We wanted to determine whether the latency/gain of the correction for a cursor jump are only influenced by the size of the cursor jump or whether they are also influenced by the need of a correction for the target to be reached. In Experiment 1, we used two target sizes (5 and 30 mm) and three cursor-jump amplitudes (5, 15, and 25 mm), so that for some target size/cursor-jump combinations, no correction would be needed to reach the target. Participants were not aware of the cursor jump, but we observed a 65% correction regardless of target size. In Experiment 2, participants pointed at a large target for which a 15-mm cursor jump never impeded target attainment. Participants modified the trajectory of their movement in the direction opposite to the cursor jump (42% of the cursor jump). Our results indicate that the latency of the correction for a cursor jump was not influenced by the size of the cursor jump or that of the target. However, the correction tailored the movement's initial impulse according to the target's characteristics.

Surveillance of fatal occupational injuries in France: 2002-2004.

BACKGROUND: Insufficient use is made of available information about workplace and commuting accidents covered by social insurance workers compensation funds in France. We sought to determine whether these data could be used to calculate national indicators for surveillance of fatal occupational injuries for 2002-2004. METHODS: We calculated the number of deaths, mortality rate, and years of potential life lost from workplace and commuting accidents (by sex, age, economic activity, and cause of accident) for employees by collecting data from eight social insurance funds in France. The number of deaths, the mortality rates, and the attributable fraction of accidental deaths due to work were estimated for both employees and self-employed workers. RESULTS: The mean annual number of employee deaths from workplace and commuting accidents reached 1,330 in 2002-2004. The mortality rate from workplace accidents (6.0 per 100,000) increased with age among men and was especially high in three sectors: agriculture-forestry-fishing, transportation, and construction.Overall, for employees and the self-employed combined, the mean annual number of deaths from workplace and commuting accidents was estimated at 1,557 (95% CI: 1,478-1,640). The attributable fraction of accidental deaths due to work for those aged 15-59 years was estimated at almost 20% among men. CONCLUSIONS: Despite data limitations, it was possible to calculate previously unknown national indicators of fatal workplace and commuting accidents and to compare them with other work-related health problems. These results are consistent with those observed in comparable industrialized countries.