Effects of Age on Motor Preparation and Restructuring

Age-related decrements in motor plan restructuring were investigated. In this experiment, older and younger adults performed a discrete aiming task that involved responses that were precued and responses that were modified at the time of an imperative signal. On 75% of the trials, the precue specified the response-stimulus (valid trials) with respect to the movement parameters of the arm (left or right) and direction (toward or away). On the remaining 25% of the trials, the response-stimulus was different from the precue (invalid trials) in that the subject was required to modify a planned movement by changing the arm to be used and/or the direction of movement. The older subjects were slower than the younger in both the valid and invalid trials. Across preparatory intervals (PI) of 500, 1,000, 1,500, and 2,000 msec, older, but not younger subjects exhibited less reaction time cost for restructuring the motor plan for the direction-change condition than for the other parameter change conditions. Since there was little apparent cost of restructuring, these findings suggest that older adults did not prepare the direction of movement, and thus found it temporally more efficient to alter direction than arm or arm and direction combined

Aging and the Restructuring of Precued Movements

A precue paradigm was used to examine the time it takes to restructure a planned motor response. Two groups of subjects, a young group, and an elderly group, performed an aiming task in which 75% of the trials involved no change of movement parameters. On remaining trials, subjects had to change one or more of the movement parameters. Elderly subjects had slower reaction times (RTs), movement times, and made more errors in both conditions. Elderly subjects had proportionally longer RTs overall, independent of restructuring a movement plan. Preparation of arm and direction also exhibited a proportional increase in RT. However, differential aging effects were found for preparation of extent. Elderly subjects were slower preparing short movements compared with long movements, whereas young subjects showed the opposite trend. These results suggest that with advancing age, operations concerned with movement-plan restructuring for arm and direction undergo a change in processing rate, whereas operations for extent undergo more extensive alteration

Age Differences in the Maintenance and Restructuring of Movement Preparation

In 2 experiments, 56 elderly (aged 65–78 yrs) and young Ss (aged 20–28 yrs) performed simple reaction time (RT), choice RT, and movement plan restructuring tasks, using a stimulus precuing paradigm. In Exp 1, the precue display (200 ms) and preparation interval (250, 500, 750, or 1,000 ms) were experimentally determined. In Exp 2, the precue display interval was S determined. For the restructuring task, the precue specified the response on 75% of the trials, enabling movement plan preparation with respect to movement parameters of arm and direction. On remaining trials, the precue incorrectly specified the response, requiring movement plan restructuring. Elderly, but not young, Ss restructured a movement plan for direction more quickly than for arm or for both parameters. These findings indicate that elderly individuals have poorer movement plan maintenance for direction than for arm and thus exhibit functional change in movement preparation processes relative to young individuals

Age Differences in Bimanual Coordination

A bimanual coordination experiment was conducted in which two groups of 10 male and female participants, elderly (67 to 75 years of age) and young (21 to 25 years of age), produced unimanual, bimanual symmetrical (equal extent amplitude), and bimanual asymmetrical (unequal extent amplitude) movements. In addition to an overall increase in performance latency, the elderly group exhibited a linear increase in response initiation (RT) with increases in task complexity similar to that of the young group. However, the elderly participants showed a proportional increase over the young participants in response execution latency (MT). Further, the elderly group had a slower RT for short movements than long movements, an effect not found in the young group. Compared with the young participants, the elderly participants showed greater asynchrony in response initiation of bimanual movements; increased inability to subsequently compensate during response execution also resulted in a greater asynchrony in response termination. These results suggest specific aging deficits in bimanual coordination processes

Synergistic Development, Test, and Qualification Approaches for the Ares I and V Launch Vehicles

The U.S. National Aeronautics and Space Administration (NASA) initiated plans to develop the Ares I and Ares V launch vehicles in 2005 to meet the mission objectives for future human exploration of space. Ares I is designed to provide the capability to deliver the Orion crew exploration vehicle (CEV) to low-Earth orbit (LEO), either for docking to the International Space Station (ISS) or docking with an Earth departure stage (EDS) and lunar lander for transit to the Moon. Ares V provides the heavy-lift capability to deliver the EDS and lunar lander to orbit. An integrated test plan was developed for Ares I that includes un-crewed flight validation testing and ground testing to qualify structural components and propulsion systems prior to operational deployment. The overall test program also includes a single development test flight conducted prior to the Ares I critical design review (CDR). Since the Ares V concept was formulated to maximize hardware commonality between the Ares V and Ares I launch vehicles, initial test planning for Ares V has considered the extensibility of test approaches and facilities from Ares I. The Ares V test plan was part of a successful mission concept review (MCR) in 2008

Herbicide-resistant weeds : from research and knowledge to future needs

Synthetic herbicides have been used globally to control weeds in major field crops. This has imposed a strong selection for any trait that enables plant populations to survive and reproduce in the presence of the herbicide. Herbicide resistance in weeds must be minimized because it is a major limiting factor to food security in global agriculture. This represents a huge challenge that will require great research efforts to develop control strategies as alternatives to the dominant and almost exclusive practice of weed control by herbicides. Weed scientists, plant ecologists and evolutionary biologists should join forces and work towards an improved and more integrated understanding of resistance across all scales. This approach will likely facilitate the design of innovative solutions to the global herbicide resistance challenge