Cognitive impairment during 5 m water immersion.

Experimental data document that human cognition remains intact down to 6 m water immersion. This, however, is difficult to reconcile with introspective observations from experienced divers, who report cognitive impairments. We hypothesized that the discrepancy might be related to the fact that previous experiments assessed abstract cognitive skills, such as mental arithmetic, which might be less sensitive to immersion than performance-related cognitive skills, such as planning of behavior that is adequate for a given situation.

Age-related deficits of dual-task walking: a review.

This review summarizes our present knowledge about elderly people's problems with walking. We highlight the plastic changes in the brain that allow a partial compensation of these age-related deficits and discuss the associated costs and limitations. Experimental evidence for the crucial role of executive functions and working memory is presented, leading us to the hypothesis that it is difficult for seniors to coordinate two streams of visual information, one related to navigation through visually defined space, and the other to a visually demanding second task.

Concurrent adaptation to four different visual rotations.

The human sensorimotor system can concurrently adapt to two different distortions without interference when the distortions are cued by different contexts. We investigated whether this holds with four distortions as well. Subjects were exposed to an interlaced sequence of +30°, -30°, +60°, and -60° visuomotor rotations as the adaptation phase, cued by combinations of workspace location and by the arm used.

Mental rotation of letters, body parts and complex scenes: separate or common mechanisms?

This study compares mental rotation with three stimuli: letters, body parts and complex scenes. Twenty-four subjects saw letters and judged whether they were mirror-reversed or not (task LETTER), saw pictures of a hand and indicated whether it was a right or a left one (task HAND), and saw drawings of a person at a table on which a weapon and a rose laid and decided whether the weapon was to the person's right or left (task SCENE). Stimuli were presented in canonical orientation or rotated by up to 180°.

Production of finely graded forces in humans: effects of simulated weightlessness by water immersion.

We have shown before that subjects exposed to a changed gravitoinertial environment produce exaggerated manual forces. From the observed pattern of findings, we argued that initial forces were exaggerated because of abnormal vestibular activity and peak forces because of degraded proprioceptive feedback. If so, only peak but not initial forces should be affected by water immersion, an environment that influences proprioceptive feedback but not vestibular activity.

Age-related decline of peripheral visual processing: the role of eye movements.

Earlier work suggests that the area of space from which useful visual information can be extracted (useful field of view, UFoV) shrinks in old age. We investigated whether this shrinkage, documented previously with a visual search task, extends to a bimanual tracking task. Young and elderly subjects executed two concurrent tracking tasks with their right and left arms.

Effects of a Visual Distracter Task on the Gait of Elderly versus Young Persons.

Seniors show deficits of dual-task walking when the second task has high visual-processing requirements. Here, we evaluate whether similar deficits emerge when the second task is discrete rather than continuous, as is often the case in everyday life. Subjects walked in a hallway, while foot proprioception was either perturbed by vibration or unperturbed.

Adaptation to mirror-reversed vision is based on directionally tuned modules.

Sensorimotor adaptation to rotated visual feedback is thought to be achieved by directionally tuned modules. Here we scrutinize whether adaptation to reversed vision utilizes similar mechanisms. Specifically, we hypothesize that adaptive transfer to unpracticed target directions is determined by the superposition of neighboring modules.

Adaptation to rotated visual feedback depends on the number and spread of target directions.

It has been proposed in the past that adaptation to rotated visual feedback is based on directionally tuned modules. Here, we investigate whether adaptation depends on the number of modules that are concurrently activated. To disambiguate the number of modules and their spatial overlap, we decided to vary the number of target directions and their spacing independently.

Proprioception plays a different role for sensorimotor adaptation to different distortions.

If proprioceptive feedback is degraded by agonist-antagonist muscle vibration, then adaptation to rotated vision remains intact while adaptation to a velocity-dependent force field worsens. Here we evaluate whether this differential effect of vibration is related to the physical nature of the distortion - visual versus mechanical - or to their kinematic coupling to the subjects' hand - velocity versus position dependent. Subjects adapted to a velocity-dependent visual distortion, to a position-dependent force, or to a velocity-dependent force; one half of the subjects adapted with, and the other half without agonist-antagonist vibration at the wrist, elbow, and shoulder.

Age-related deficits of dual-task walking: the role of foot vision.

Previous studies found that age-related deficits of dual-task walking emerge with secondary tasks that require substantial visual processing, but are absent with tasks that require little or no visual processing. We evaluated whether this is so because visual tasks typically interfere with foot vision, on which older persons depend more heavily than young ones. Young (25±3 years) and older (69±5 years) subjects walked along a straight path and checked boxes on a handheld panel, separately or concurrently.

Changes of locomotion in old age depend on task setting.

Background: Laboratory settings may differ from everyday life with respect to factors such as attention, motivation, intention, and self-efficacy. Since those factors are likely to influence subjects' performance on locomotor tasks, we evaluated whether the age-related changes of locomotion previously observed under laboratory conditions are equally present in a real life-like scenario.

Methods: 15 young and 15 older subjects walked along a marked path of 25 m length and 0.

Cognitive demand of human sensorimotor performance during an extended space mission: a dual-task study.

Introduction: Two previous single-case studies found that the dual-task costs of manual tracking plus memory search increased during a space mission, and concluded that sensorimotor deficits during spaceflight may be related to cognitive overload. Since dual-task costs were insensitive to the difficulty of memory search, the authors argued that the overload may reflect stress-related problems of multitasking, rather than a scarcity of specific cognitive resources. Here we expand the available database and compare different types of concurrent task.

An experimental paradigm to compare motor performance under laboratory and under everyday-like conditions.

Research findings on human motor skills may not necessarily hold in everyday life, since laboratory and everyday scenarios typically differ with respect to the subjects' attention to the skill, their motivation to perform at their best, the goals they try to achieve, and the mode of movement initiation - extrinsic versus intrinsic. Here we present an experimental approach which can be used to substantiate the hypothesized effects of laboratory (L) versus everyday (E) settings on one type of motor skill, i.e.

Sensorimotor adaptation is influenced by background music.

It is well established that listening to music can modify subjects' cognitive performance. The present study evaluates whether this so-called Mozart Effect extends beyond cognitive tasks and includes sensorimotor adaptation. Three subject groups listened to musical pieces that in the author's judgment were serene, neutral, or sad, respectively.

Simulated flight path control of fighter pilots and novice subjects at +3 Gz in a human centrifuge.

Background: We have previously shown that subjects produce exaggerated manual forces in +3 Gz. When subjects execute discrete flight path changes in a flight simulator, their performance is less stable in +3 Gz than in +1 Gz. Here we explore whether Gz-related deficits are found with continuous flight path changes.

Adaptation of eye and hand movements to target displacements of different size.

Previous work has documented that the direction of eye and hand movements can be adaptively modified using the double-step paradigm. Here we report that both motor systems adapt not only to small direction steps (5 degrees gaze angle) but also to large ones (28 degrees gaze angle). However, the magnitude of adaptation did not increase with step size, and the relative magnitude of adaptation therefore decreased from 67% with small steps to 15% with large steps.

Stability of simulated flight path control at +3 Gz in a human centrifuge.

Introduction: Earlier studies have shown that naïve subjects and experienced jet pilots produce exaggerated manual forces when exposed to increased acceleration (+Gz). This study was designed to evaluate whether this exaggeration affects the stability of simulated flight path control.

Methods: We evaluated naïve subjects' performance in a flight simulator which either remained stationary (+1 Gz), or rotated to induce an acceleration in accordance to the simulated flight path with a mean acceleration of about +3 Gz.

Is sensorimotor adaptation to position- and velocity-dependent visual distortions based on distinct adaptive processes?

It is widely held that sensorimotor adaptation to different distortions is brought about by separate, distortion-specific processes which compete for the limited resources of short-term motor memory when they are activated in close temporal succession. Here we scrutinized this view by exposing participants sequentially to two distortions of equal or of opposite polarity, one proportional to the position, and the other to the velocity of their hand. We found movement errors to be largest in participants who were pre-adapted to a distortion of different type and opposite polarity, smaller in novice participants, and smaller still in participants who were pre-adapted to a distortion of different type and same polarity.

Mechanisms for visuomotor adaptation to left-right reversed vision.

Behavioral studies suggest that the adaptation of planar arm movements to rotated visual feedback is achieved by the interplay of a gradual process which slowly rotates participants' responses by up to +/-90 degrees , and a discrete process which changes the responses by means of axis inversion. The processes for adaptation to left-right reversed visual feedback are far less well understood. To clarify this issue, 12 healthy participants performed pointing movements to targets presented in eight different directions, before and during exposure to left-right reversed visual feedback.

Exaggerated force production in altered Gz-levels during parabolic flight: the role of computational resources allocation.

The purpose of the present experiment was to examine whether the previously observed exaggerated isometric force production in changed-Gz during parabolic flight (Mierau et al. 2008) can be explained by a higher computational demand and, thus, inadequate allocation of the brain's computational resources to the task. Subjects (n = 12) were tested during the micro-Gz, high-Gz and normal-Gz episodes of parabolic flight.

Visuomotor adaptive improvement and aftereffects are impaired differentially following cerebellar lesions in SCA and PICA territory.

The aim of the present study was to elucidate the contribution of the superior and posterior inferior cerebellum to adaptive improvement and aftereffects in a visuomotor adaptation task. Nine patients with ischemic lesions within the territory of the posterior inferior cerebellar artery (PICA), six patients with ischemic lesions within the territory of the superior cerebellar artery (SCA) and 17 age-matched controls participated. All subjects performed center-out reaching movements under 60 degrees rotation of visual feedback.

Visual field motion effects on the production of manual forces and displacements.

Background: We have previously shown that subjects produce exaggerated arm forces when exposed to three times the normal gravitational acceleration (+3 Gz), and that this deficit is not related to direct mechanical effects, faulty proprioception, or increased cognitive load. Here we investigate whether it is related to vestibular activity.

Methods: Novice subjects observed a stationary, upward or downward moving visual field while producing pretrained arm forces (Exp.

On the use of different spatial reference frames for movement control.

Previous work has shown that amplitude and direction are two independently controlled parameters of aimed arm movements, and performance, therefore, suffers when they must be decomposed into Cartesian coordinates. We now compare decomposition into different coordinate systems. Subjects pointed at visual targets in 2-D with a cursor, using a two-axis joystick or two single-axis joysticks.

Dual-task costs while walking increase in old age for some, but not for other tasks: an experimental study of healthy young and elderly persons.

Background: It has been suggested in the past that the ability to walk while concurrently engaging in a second task deteriorates in old age, and that this deficit is related to the high incidence of falls in the elderly. However, previous studies provided inconsistent findings about the existence of such an age-related dual-task deficit (ARD). In an effort to explain this inconsistency, we explored whether ARD while walking emerges for some, but not for other types of task.