Ann Lavrysen

The control of sequential aiming movements: the influence of practice and manual asymmetries on the one-target advantage.

The present experiment was conducted to explore the effect of practice on the one-target advantage in manual aiming, as well as asymmetries in intermanual transfer of training. Reaction and movement times for the first movement were longer in the 2-target than in the 1-target task, regardless of the amount of practice, hand preference and practice hand. When two movements were required, peak velocity was lower and, proportionally, more time was spent after peak velocity. Our kinematic results suggest that the one-target advantage is related to both predefined strategies as well as movement implementation processes during execution. Therefore, an integration of advance planning and on-line explanations for the one-target advantage is suggested. Regarding manual asymmetries, right-handers showed more transfer of training from the left to the right hand than vice versa. Left-handers exhibited a reversed pattern of asymmetric transfer of training to right-handers, but they were more disadvantaged using their non-dominant hand. These latter two findings have implications for models of manual asymmetry and upper limb control.

Effect of visual information on step-tracking movements in patients with intention tremor due to multiple sclerosis

The effect of visual information on step-tracking movements was studied in 18 patients with intention tremor due to multiple sclerosis (MS) and 15 healthy controls. Participants performed a slow wrist step-tracking task with stationary targets under five visual feedback conditions. The display of the target and movement cues was selectively withdrawn to examine the effects of visual information on intention tremor and movement accuracy. Results showed that intentio n tremor was most pronounced when visual display of both target and movement cues was available. Withdrawing visual information of the limb movement reduced tremor more than withdrawing the visual display of the target cues. Both the patient and control group was less accurate when the display of limb movement was occluded. Patients, however, were more dependent on visual information of the limb movement for accurate motor performance than healthy controls. When the visual display of the limb movement was partially occluded between or near to the targets, tremor decreased without deterioration of movement accuracy.

Online movement control in multiple sclerosis patients with tremor: Effects of tendon vibration

Patients with intention tremor due to multiple sclerosis (MS) exhibit an increased reliance on visual feedback in the sensorimotor control of slow goal‐directed movements. In the present study, the use of proprioceptive information was investigated in MS patients with intention tremor compared to MS patients without tremor and healthy controls. Tendon vibration was applied to the wrist extensor muscles during a memory‐guided slow wrist step‐tracking task to investigate the use of muscle spindle afferent information in online movement control. A significant reduction of movement amplitude was induced by tendon vibration in all three groups, but the effect was found to be smaller in MS patients with tremor (28%) than in subjects without tremor (50%). Vibration also induced an increase of overall tremor amplitude in the MS tremor group; however, its effect on movement amplitude was not directly related to (changes in) tremor severity. The results suggest that the decreased online use of proprioceptive information in MS patients with tremor reflects an adaptation over time to cope with a tremor‐related noisy background. Abnormalities in proprioceptive processing may explain why MS patients with tremor show an increased reliance on visual feedback for online motor control.

Interaction between eye and hand movements in multiple sclerosis patients with intention tremor.

Deficient eye and hand movements are present in patients with multiple sclerosis. In the present study, eye and hand movements were simultaneously measured during visually guided wrist step‐tracking tasks in 16 patients with intention tremor and 15 healthy controls. The coupling between eye and hand movements was analyzed during simultaneous eye–hand tracking, and interactions were studied by comparing the coordinated eye–hand condition with isolated eye‐ or hand‐tracking conditions. Despite movement abnormalities, the onset of eye and hand movements was highly correlated and an invariant coupling between the saccadic completion time and hand peak velocity was found, suggesting that the temporal coupling was very much preserved. The differences between the experimental tracking conditions suggest that, in MS patients with intention tremor, the ocular system influenced the hand movements. Intention tremor amplitude was reduced when there was no preceding saccadic eye movement, whereas conversely, eye movements were not affected by different hand tremor severity.

Intention tremor during manual aiming: a study of eye and hand movements:

A ccurate goal-directed movements toward a visual target require a precise coordination of both the oculomotor and limb motor systems. Intentio n tremor and eye movement deficits are frequently observed in multiple sclerosis (MS). The goal of this study was to examine the characteristics of intentio n tremor and simultaneously produced eye movements during rapid goal-directed movements. Eye and hand movements were synchronously measured in 16 MS patients with intentio n tremor and 16 control subjects. Manual performances of the patient group were character ized by a delayed onset, slower executio n and aiming inaccuracies. In line with the clinically defined picture of intention tremor, differences between patients and control subjects were most pronounced toward the end of the movement. Dependent variables were obviously greater in MS patients compared with control subjects, and correlated well with clinical outcome measures. The application of an inertial load to the limb did not show any effect on intention tremor. In addition to impaired limb coordination, evidence has been found that eye movements, too, were abnormal in patients compared with control subjects. Moreover, eye and hand movement deficits seemed to be closely related, suggesting a common underlying command structure. Inaccurate eye movements were likely to hamper an accurate motor performance of the hand.

The Costs of Taking It Slowly Fast and Slow Movement Timing in Older Age

We investigated adult age-differences in timing control of fast vs. slow repetitive movements using a dual-task approach. Twenty-two young (M = 24.23 yr) and 22 older adults (M = 66.64 yr) performed three cognitive tasks differing in working memory load and response production demands and they tapped series of 550-ms or 2100-ms target intervals. Single-task timing was comparable in both groups. Dual-task timing was characterized by shortening of produced intervals and increases in drift and variability. Dual-task costs for both cognitive and timing performances were pronounced at slower tapping tempos, an effect exacerbated in older adults. Our findings implicate attention and working memory processes as critical components of slow movement timing and sources of specific challenges thereof for older adults.

Factors underlying age-related changes in discrete aiming

Abstract Age has a clear impact on one’s ability to make accurate goal-directed aiming movements. Older adults seem to plan slower and shorter-ranged initial pulses towards the target, and rely more on sensory feedback to ensure endpoint accuracy. Despite the fact that these age-related changes in manual aiming have been observed consistently, the underlying mechanism remains speculative. In an attempt to isolate four commonly suggested underlying factors, young and older adults were instructed to make discrete aiming movements under varying speed and accuracy constraints. Results showed that older adults were physically able to produce fast primary submovements and that they demonstrated similar movement-programming capacities as young adults. On the other hand, considerable evidence was found supporting a decreased visual feedback-processing efficiency and the implementation of a play-it-safe strategy in older age. In conclusion, a combination of the latter two factors seems to underlie the age-related changes in manual aiming behaviour.

The type of visual information mediates eye and hand movement bias when aiming to a Müller–Lyer illusion

Aiming bias typically influences perception but action towards the illusory stimulus is often unaffected. Recent studies, however, have shown that the type of information available is a predictor for the expression of action bias. In the present cyclical aiming experiment, the type of information (retinal and extra-retinal) was manipulated in order to investigate the differential contributions of different cues on both eye and hand movements. The results showed that a Müller–Lyer illusion caused very similar perturbation effects on hand and eye-movement amplitudes and this bias was mediated by the type of information available on-line. Interestingly, the impact of the illusion on goal-directed movement was smaller, when information about the figure but not the hand was provided for on-line control. Saccadic information did not influence the size of the effect of a Müller–Lyer illusion on hand movements. Furthermore, the illusions did not alter the eye–hand coordination pattern. The timing of saccade termination was strongly linked to hand movement kinematics. The present results are not consistent with current dichotomous models of perception and action or movement planning and on-line control. Rather, they suggest that the type of information available for movement planning mediates the size of the illusory effects. Overall, it has been demonstrated that movement planning and control processes are versatile operations, which have the ability to adapt to the type of information available.

Unraveling the relationship between trait negative affectivity and habitual symptom reporting

Objective In two studies, we aimed at further elucidating the relationship between trait negative affectivity (NA) and habitual symptom reporting (HSR) by relating these variables to measures of executive function, trait questionnaires, and effects of emotion induction. Methods Healthy female participants (N = 75) were selected on their scores for trait NA and for the Checklist for Symptoms in Daily Life. Three groups were compared: (1) low NA-low HSR; (2) high NA-low HSR; and (3) high NA-high HSR (low NA-high HSR did not occur). In study 1, participants underwent a Parametric Go/No-go Task and a Stroop Color-Word test, and trait questionnaires measured alexithymia and absorption. Forty-five participants (N = 15 in each group) were further engaged in study 2 to induce state NA using an affective picture paradigm. Results Impaired inhibition on the Stroop and Go/No go Task characterized high trait NA, but not high HSR, whereas alexithymia and absorption were elevated in HSR, regardless of trait NA. Negative picture viewing induced elevated state NA in all groups, but only high HSR also reported more bodily symptoms. This effect was moderated, but not mediated by state NA. Conclusion High trait NA is a vulnerability factor but not a sufficient condition to develop HSR. Deficient inhibition is related to the broad trait of NA, whereas the moderating effect of state NA on symptom reporting is specific for high HSR. Understanding processes related to alexithymia and absorption may specifically help to explain elevated HSR.

Hemispheric asymmetries in eye-hand coordination

Manual asymmetries in limb kinematics and eye-hand coordination have usually been attributed to differences in online processing capabilities between the left and the right cerebral hemisphere. In the present fMRI experiment, we examined in right handers the brain areas involved in eye-hand coordination with either the left or the right hand. Although temporal and spatial accuracy was equal for left- and right-hand movements, manual asymmetries were found in behavioral and neurophysiologic data, suggesting an asymmetric mode of control for left vs. right eye-hand coordination. For left eye-hand coordination, peak velocity and saccade completion occurred earlier than for the contralateral movements, suggesting that there was more time needed for homing-in on the target. When using the right hand, there was more activation in occipital areas. This might indicate a more intense visual processing or visualization of the target locations. When using the left hand, there was more activation in sensorimotor areas, frontal areas and cerebellum. This might point toward more processing effort. Left-hand movements may be considered as more difficult than right-hand movements by right-handed participants. Alternatively and more likely, these findings might reflect a difference in attention or resources attributed to different aspects of the tasks because of the different functional specializations of both hand/hemisphere systems.