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Biomedical subjects

G P Van Galen

Publications and source records attributed to G P Van Galen.

9 recordsLinked to original sources
PubMed2002

The breakdown of Fitts' law in rapid, reciprocal aiming movements.

According to Fitts' law, there is speed-accuracy trade-off in a wide variety of discrete aiming movements. However, it is unknown whether the same law applies to cyclic aiming movements. In the present study, a comparison is made between discrete versus cyclic aiming movements. A group of 24 healthy participants made graphical pen movements in 12 different aiming tasks in which successive finger and wrist movements were emphasized, consecutively executed as discrete and cyclic movements and varying in three target widths. In the cyclic condition, aiming movements consisted of back-and-forth movements that were performed in immediate succession for 20 s. In the discrete condition, back-and-forth aiming movements were drawn as 20 single strokes, starting after a go signal and stopping after reaching the target area. The targets had various levels of spatial accuracy and the movements had different directions (from lower left to upper right; from lower right to upper left) elicit either predominantly wrist or finger movements. The amount of information processed per unit of time (bits per second; index of performance, IP), tangential velocity, the pen pressure, and the ratio of peak-over-mean velocity were studied to gain understanding about the differences in control between discrete and cyclic movements. It was found that the IP and movement velocity were almost twice as large in cyclic versus discrete movements. In contrast, the axial pen pressure and the ratios of peak-over-mean velocity were much lower in cyclic movements (1.24 N versus 0.94 N; 2.26 N versus 1.81 N). The results of our study indicate that the predicted constant IP does not hold for rapid cyclic aiming movements and that speed-accuracy trade-off is different. It is concluded that cyclic movements exploit the energetic and physiological properties of the neuromotor system. Expected differences in brain activity related to discrete and cyclic aiming movements are discussed as well as several neurophysiological mechanisms, which predict more economic force recruitment and information processing in cyclic than in discrete movements.

Adult↗
PubMed2001

Improving obstacle detection by redesign of walking canes for blind persons.

This paper describes an experiment in which the performance of cane walkers with the traditional straight long cane and a redesigned cane, the curved cane, was compared. The curved cane has a curve where the tip touches the ground. Participants were 18 experienced cane walkers who were totally blind. The aspects of cane walking that were investigated included obstacle detection, drop-off (slope) detection and walking speed. The performance with both canes was investigated in two different ways: (1) by means of constructed courses in which objective measures of cane walking were derived; and (2) by means of more qualitative measures based on the participants' experiences with the curved cane during a 3-week try-out period. Results showed that obstacle-detection was significantly better with the curved cane, whereas drop-off detection and walking speed were comparable for the two canes. The participants' experiences mirrored these results.

Adult↗
PubMed2000

Modulation of the startle response during human gait.

While many studies have shown that there is a phase-dependent modulation of proprioceptive and exteroceptive reflexes during gait, little is known about such modulation for auditory reflexes. To examine how startle reactions are incorporated in an ongoing gait pattern, unexpected auditory stimuli were presented to eight healthy subjects in six phases of the step cycle during walking on a treadmill at 4 km/h. For both legs, electromyographic activity (EMG) was recorded in the biceps femoris (BF), the rectus femoris (RF), the tibialis anterior (TA), and the soleus (SO). In addition, stance and swing phases of both legs, along with knee angles of both legs and the left ankle angle, were measured. All subjects showed various response peaks. Responses with latencies of approximately 60 ms (F1), approximately 85 ms (F2), and approximately 145 ms (F3) were found. The amplitude of the reflex responses was dependent on the timing of the startle stimulus in the step cycle. Although the startle response habituated rapidly, the phase-dependent modulation pattern generally remained the same. The phase-dependent amplitude modulations were not strictly correlated with the modulation of the background activity. The TA even showed a transition from facilitatory F2 responses during stance to suppressive responses during midswing. Responses were observed in both flexors and extensors, often in coactivation, especially during stance. Furthermore the gait characteristics showed a shortening of the subsequent step cycle and a small decrease in the range of motion of ankle and knees. These results suggest that the responses are adapted to achieve extra stability dependent on the phase of the step cycle. However, even in the first trials, the changes in kinematics were small allowing a smooth progression of gait.

Adult↗
PubMed1998

Auditory stress effects on preparation and execution of graphical aiming: a test of the neuromotor noise concept.

Effects of physical and mental stress, on the preparation and execution of a psychomotor task were studied to test the applicability of the neuromotor noise concept (Van Gemmert and Van Galen, 1997) as an explanation of stress effects. Central to this notion is that both physical stress and mental load raise neuromotor noise levels in the human information processing system. It is proposed that increased levels of neuromotor noise lead to decreased processing times during task preparation (activation effect), decreased or increased reaction times during task initiation, depending on task difficulty (impoverished signal-to-noise effect) and increased limb stiffness during task execution (biomechanical filtering effect). To test these predictions, an experiment was conducted in which two types of auditory stressors, physical stress and mental load, were manipulated across the stages of preparation, initiation, and execution of a graphical aiming task. The results confirmed the notion that the neuromotor noise concept is a tenable approach to explain the effects of stress on human performance.

Acoustic Stimulation↗
PubMed1998

Texture information in tactual space perception.

The significance of texture as a source of information in tactual space perception was studied using a linear positioning task. A spatial texture gradient, whose elements changed with position and distance, a homogeneous raised-element pattern and a smooth surface were used. Participants had to reproduce locations and distances on these surfaces under various conditions. In active conditions, participants moved their indexfinger across the surface. In passive conditions, the texture was moved beneath the indexfinger of the participant. In conditions with equal movement speed, movement speeds' of criterion and reproduction phase were matched, in conditions with unequal movement speed, they did not match. The largest errors were obtained for the combined passive movement-unequal movement speed conditions. In these conditions, differences between textures were visible for signed and unsigned errors, indicating that textures may differ in the cutaneous specification of distance and location.

Adult↗
PubMed1997

Dysgraphia in children: lasting psychomotor deficiency or transient developmental delay?

A longitudinal design was applied to differentiate between normal variations of psychomotor development and lasting handwriting deficiency (dysgraphia). Sixteen primary school children were tested with writing tasks that were recorded on a computer-monitored'XY tablet. These tasks represented different modules of the handwriting model of Van Galen (1991). Dependent variables were spatial errors, movement time, movement dysfluencies, trajectory length, stroke curvature, and the degree of neuromotor noise in the movement velocity profiles. The latter variable was measured by means of Power Spectral Density Analysis of the movement velocity signal, which revealed that movements of poor writers were substantially more noisy than those of proficient writers, with a noise peak in the region of neuromotor tremor. At the same time, the poor writers were less accurate. It was concluded that control of spatial accuracy rather than allograph retrieval or size control is the discriminating feature in dysgraphic children. Moreover, poor writers do not catch up with their peers within the 1 year time span tested.

Agraphia↗
PubMed1997

Stress, neuromotor noise, and human performance: a theoretical perspective.

A new theory on stress and human performance is proposed in which physical and cognitive stressors enhance the level of neuromotor noise in the information-processing system. The neuromotor noise propagates in time and space. A 2nd assumption states that such noise facilitates easy tasks but disrupts complex tasks. In 4 experiments, 2 graphic tasks (number writing and graphic aiming) were crossed with 2 stressors (cognitive stress from a dual-task situation and physical stress in the form of loud auditory noise). Reaction time (RT), movement time (MT), and axial pen pressure were measured. In the RT phase, stress was predicted to lead to decreased RT with easy tasks and to increased RT with difficult tasks. In the execution phase, biomechanical adaptation to enhanced levels of noise was expected to manifest in higher levels of limb stiffness. In all 4 experiments, an increase of axial pen pressure with higher levels of stress evidenced the generality of biomechanical adaptation as a response to stress. RT and MT showed differential effects among the 4 experiments.

Adolescent↗
PubMed1990

Effects of motor programming on the power spectral density function of finger and wrist movements.

Power spectral density analysis was applied to the frequency content of the acceleration signal of pen movements in line drawing. The relative power in frequency bands between 1 and 32 Hz was measured as a function of motoric and anatomic task demands. Results showed a decrease of power at the lower frequencies (1-4 Hz) of the spectrum and an increase in the middle (9-12 Hz), with increasing motor demands. These findings evidence the inhibition of visual control and the disinhibition of physiological tremor under conditions of increased programming demands. Adductive movements displayed less power than abductive movements in the lower end of the spectrum, with a simultaneous increase at the higher frequencies. The relevance of the method for the measurement of neuromotor noise as a possible origin of delays in motor behavior is discussed.

Adult↗