Marc Dalecki

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 persons right or left (task SCENE). Stimuli were presented in canonical orientation or rotated by up to 180°. Our analyses focused on intra-subject correlations between reaction times of the different tasks. We found that reaction times for stimuli in canonical orientation co-varied in HAND and LETTER, the increase of reaction times with increasing object rotation co-varied in HAND and SCENE, and reaction times for 180° rotations co-varied between all tasks. We suggest that basic processes like visual perception and decision-making are distinct for scenes versus letters and body parts, that the mechanism for mental rotation of letters is distinct from that for mental self- and body part rotation, and suggest an extra mechanism for 180° rotations that shared among all tasks. These findings confirm and expand hypotheses about mental rotation that were based on comparisons of between-subject means.

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. The present study was undertaken to scrutinize this prediction. Twelve subjects sat in a chair once immersed in water and once on dry land, while producing pre-trained isometric forces with a joystick. In a control experiment, subjects performed a four-choice reaction-time task. During the joystick task, produced initial forces were comparable in water and on land, while peak (+24%) and end forces (+22%) were significantly higher in water, as was their reaction time (+6%). During the control task, reaction time was comparable in water and on land. Our findings corroborate the above notion that initial forces increase when the vestibular system is stimulated (gravitoinertial change, visual field motion, but not water immersion), while peak forces increase when proprioceptive feedback is degraded (probably all three scenarios) and are not corrected until response end. Our findings further confirm the absence of cognitive slowing in simple-choice reaction tasks under shallow-water immersion conditions.

Prolonged cognitive–motor impairments in children and adolescents with a history of concussion

Aim: We investigated whether children and adolescents with concussion history show cognitive–motor integration (CMI) deficits. Method: Asymptomatic children and adolescents with concussion history (n = 50; mean 12.84 years) and no history (n = 49; mean: 11.63 years) slid a cursor to targets using their finger on a dual-touch-screen laptop; target location and motor action were not aligned in the CMI task. Results: Children and adolescents with concussion history showed prolonged CMI deficits, in that their performance did not match that of no history controls until nearly 2 years postevent. Conclusion: These CMI deficits may be due to disruptions in fronto-parietal networks, contributing to an increased vulnerability to further injury. Current return-to-play assessments that do not test CMI may not fully capture functional abilities postconcussion.

Changed joint position sense and muscle activity in simulated weightlessness by water immersion.

BACKGROUND Previous studies suggested that proprioceptive feedback for passive arm positioning and isometric forces deteriorates under water. Here we investigate whether a similar deficit exists for active arm positioning. Since deficits were attributed to a reduced muscle tone but findings about muscle tone in water are ambiguous, we re-evaluated this issue. METHODS With their right forearm, 24 subjects reproduced visual templates which showed a forearm at 45 degrees, 90 degrees, and 135 degrees orientations in the sagittal plane on land (Dry) and during water immersion (Wet). Mean reproduction error and its standard deviation were calculated in allocentric (space-referenced) and egocentric (body-referenced) coordinates. Additionally, 12 of the 24 subjects also participated in an experiment where relaxed left arm EMG was registered in Wet and Dry. RESULTS Mean error was comparable in Wet (7.72 degrees) and Dry (6.79 degrees), but error variability was significantly smaller in Wet (7.52 degrees) than in Dry (9.58 degrees). Errors in allocentric (3.42 degrees) differed from egocentric coordinates (11.08 degrees), independent of Wet and Dry. Resting EMG was significantly lower in Wet (3.02 microV) than in Dry (3.73 microV). DISCUSSION Proprioceptive feedback for active arm movements is enhanced under water, probably due to high water viscosity, which increases spindle afferents during active but not passive arm movements or isometric responses. We found no evidence that the reference frame for orientation judgments differ between Wet and Dry. Muscle tone of the relaxed arm was reduced under water, corroborating that water immersion degrades proprioception during isometric tasks and passive arm positioning. This is probably not relevant for active arm movements, which seem to increase rather than decrease muscle force to overcome waters viscosity.

Human performance in a realistic instrument-control task during short-term microgravity

Previous studies have documented the detrimental effects of microgravity on human sensorimotor skills. While that work dealt with simple, laboratory-type skills, we now evaluate the effects of microgravity on a complex, realistic instrument-control skill. Twelve participants controlled a simulated power plant during the short-term microgravity intervals of parabolic flight as well as during level flight. To this end they watched multiple displays, made strategic decisions and used multiple actuators to maximize their virtual earnings from the power plant. We quantified control efficiency as the participants’ net earnings (revenue minus expenses), motor performance as hand kinematics and dynamics, and stress as cortisol level, self-assessed mood and self-assessed workload. We found that compared to normal gravity, control efficiency substantially decreased in microgravity, hand velocity slowed down, and cortisol level and perceived physical strain increased, but other stress and motor scores didn’t change. Furthermore, control efficiency was not correlated with motor and stress scores. From this we conclude that realistic instrument control was degraded in short-term microgravity. This degradation can’t be explained by the motor and/or stress indicators under study, and microgravity affected motor performance differently in our complex, realistic skill than in the simple, laboratory-type skills of earlier studies.

EEG coherence during mental rotation of letters, hands and scenes

The purpose of the present study was to investigate differences in the electrocortical synchronization pattern during mental rotation of three different object categories as well as six different rotation angles. Therefore, event-related coherence of the electroencephalographic (EEG) activity between selective frontal and parietal electrode pairs of ten subjects was measured during the performance of a mental rotation task consisting of rotation of letters, hands and scenes. Statistical analysis showed an increased coherence of frontal and parietal electrode pairs for the condition LETTER in comparison to the other conditions in the alpha1- (8.5-10 Hz) and alpha2-band (10, 5-12 Hz) supporting the notion of different mental rotation mechanisms for externally and internally represented objects. Additionally decreased coherence of the frontal and parietal electrode pairs was found for the rotation angles 30° to 150° in comparison to the 0° and 180° rotations for the alpha1- and alpha2-band as well as the gamma frequency band (30-45 Hz). It is assumed that this decrease of synchronization reflects the mental rotation process implying that the mental rotation process of 180° differs from the rotation process of all other rotation angles.

Title: fit2dive - A field test for assessing the specific capability of underwater fin swimming with SCUBA

Exercise modalities such as cycle ergometry do not mimic the specific movements of fin swimming underwater. Therefore, there is a need to develop a specific diving capability assessment procedure. The purpose of the study was the application of a standardized field test to assess and rate underwater swimming performance. The fit2dive-test consists of an incremental protocol that is performed in a pool (<5 m depth). The underwater swimming speed is increased stepwise by 0.2 m·s-1, starting with 0.4 m·s-1 until the subject’s subjective exhaustion is attained. Time of break-off (fit2dive-time), swimming technique (e.g. range of motion (ROM) of hip and knee joints) and equipment configuration was recorded via a standardized checklist. Subjects with the highest hip and knee flexion had lower fit2dive-times (373 ± 119 s; p<0.01) than those in the normal hip and knee flexion ROM category (448 ± 104 s). Further, divers using full foot fins had significantly higher (p<0.001) fit2dive-times (474 ± 97 s) than divers with adjustable strap fins (375 ± 104 s). The fit2dive test indicates the specific capability of underwater fin swimming. The results allow identifying weak factors such as underwater swimming technique or equipment configuration.

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. A, N = 12) or displacements (Exp. B, N = 12); a control group produced no motor responses and their arm EMG was registered (Exp. C, N = 12). RESULTS Produced forces and EMG were higher with the moving than with the stationary field, irrespective of field direction (initial force +42%; peak force +20%, biceps brachii EMG +21%). Produced displacements were comparable with the moving and stationary field. DISCUSSION The present pattern of findings is similar to that yielded previously in +3 Gz, which supports the existence of a common underlying mechanism. Specifically, we suggest that +3 Gz and vertical field motion stimulate the vestibular system, and that the observed exaggeration of produced force is due to vestibular modulation of descending volitional motor commands. The fact that displacements were not affected by +3 Gz and moving visual fields would then indicate that forces and displacements are controlled through distinct pathways which interact differently with the vestibular system.

Isometric Force Exaggeration in Simulated Weightlessness by Water Immersion: Role of Visual Feedback

BACKGROUND Previous studies reported that humans produce exaggerated isometric forces (20-50%) in microgravity, hypergravity, and under water. Subjects were not provided with visual feedback and exaggerations were attributed to proprioceptive deficits. The few studies that provided visual feedback in micro- and hypergravity found no deficits. The present work was undertaken to find out whether visual feedback can reduce or eliminate isometric force exaggerations during shallow water immersion, a working environment for astronauts and divers. METHODS There were 48 subjects who had to produce isometric forces of 15 N with a joystick; targets were presented via screen. Procedures were similar to earlier studies, but provided visual feedback. Subjects were tested 16.4 ft (5 m) under water (WET) and on dry land (DRY). Response accuracy was calculated with landmarks such as initial and peak force magnitude, and response timing. RESULTS Initial force and response timing were equal in WET compared to DRY. A small but significant force exaggeration (+5%) remained for peak force in WET that was limited to directions toward the trunk. DISCUSSION Force exaggeration under water is largely compensated, but not completely eliminated by visual feedback. As in earlier studies without visual feedback, force exaggeration manifested during later but not early response parts, speaking for impaired proprioceptive feedback rather than for erroneous central motor planning. Since in contrast to micro/hypergravity, visual feedback did not sufficiently abolish force deficits under water, proprioceptive information seems to be weighted differently in micro/hypergravity and shallow water immersion, probably because only the latter environment produces increased ambient pressure, which is known to induce neuronal changes.

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. METHODS Novice subjects and fighter pilots sat in a high-fidelity flight simulator equipped with the reproduction of the Eurofighter 2000 cockpit, including the realistic flight stick, and pursued continuous altitude changes of a target airplane in +1 Gz and +3 Gz. Subjects also produced verbal responses in a Stroop task. Pursuit and Stroop tasks were administered alone and concurrently. RESULTS Flight instability increased in +3 Gz compared to +1 Gz in novices (+46%), but not in pilots (+3%), and even there only during the first minute. Flight performance improved after the first minute in both subject groups. Stroop reaction time was higher in novices (+5.27%) than in pilots (+3.77%) at +3 Gz. Dual-task costs did not differ between groups or Gz levels. DISCUSSION Deficits of force production in high Gz are largely compensated for when subjects apply forces to produce a continuously changing flight path. This compensation seems not to require additional cognitive resources and may be achieved by using visual feedback. Force production deficits in high Gz seem to have no appreciable effects on flight performance and cognitive load of experienced pilots using a force-plus-displacement stick in +3 Gz. It remains to be shown whether this conclusion extends to purely isometric sticks and to higher Gz levels.