Biomedical subjects

S Krafczyk

Publications and source records attributed to S Krafczyk.

24 records · Page 2Linked to original sources

PubMed1984

Interaction between perceived self-motion and object-motion impairs vehicle guidance.

When one is riding in a vehicle, perceptual thresholds for motion of objects are significantly elevated above those determined under corresponding but simulated conditions in the laboratory without concurrent self-motion perception. Authorities on road traffic accidents should thus consider an additional perceptual time of at least 300 milliseconds for detecting critical changes in headway beyond the usual reaction time. Detection times thus corrected consequently lead to an alteration of our conception of safe intervehicle distances in a convoy. This elevation of thresholds for object-motion during self-motion, with its consequences for visual control of vehicle guidance, can be seen as a disadvantageous side effect of an otherwise beneficial space-constancy mechanism, which provides us with a stable world during locomotion.

Automobile Driving↗

PubMed1983

Oscillopsia and retinal slip. Evidence supporting a clinical test.

A clinical bedside test for oscillopsia is described for patients suffering from an acute deficiency of compensatory eye movements due either to inappropriate pursuit eye movements or a defective vestibulo-ocular reflex (VOR). This test involves quantitative measurement of the amplitude of apparent image motion (oscillopsia) during head oscillations with frequencies of 1 or 2 Hz, +/- 20 deg amplitude. It was found that normals show no oscillopsia at 1 Hz whereas patients with acute disorders do. In subacute diseases of eye-head co-ordination, however, recordings of head and eye movements revealed a dissociation between net retinal slip and oscillopsia, with the magnitude of the latter being appreciably smaller than the former. This was interpreted as indicating a central suppression mechanism initiated by the acute eye movement deficiency. The results are discussed in terms of an inhibitory interaction between self and object motion perception which produces elevated thresholds for the detection of image motion.

Adult↗

PubMed1982

[Visual prevention from motion sickness in cars].

The differential effects of vision on motion sickness in cars were tested under real road conditions using linear accelerations, in order to confirm earlier laboratory results on visual modulation of vestibular nausea induced by angular accelerations of the body. The 18 voluntary subjects were exposed to repetitive braking maneuvers (linear accelerations: 0.1-1.2 g) on a highway. The simultaneous visual stimulus conditions for the 3 separate days were: I) eyes open, visual control of car motion; II) eyes closed; III) eyes open, artificial stationary visual field (reading). The severity of motion sickness (magnitude estimation 1-10) was a function of the visual stimulus condition with significant differences among these conditions: I) moderate nausea (less than 1) with adequate visual motion perception; II) medium nausea (approximately equal to 2) with eyes closed and somatosensory-vestibular excitation only; III) strong nausea (greater than 5) with conflicting sensory input, when vestibular acceleration is in disagreement with the visual information of no movement. Providing ample peripheral vision of the relatively moving surround is the best strategy to alleviate car sickness.

Acceleration↗

PubMed1981

Postural imbalance with head extension: improvement by training as a model for ataxia therapy.

Head extension may cause a physiological vertigo and postural imbalance separate and distinct from basilar insufficiency. This physiological imbalance mainly is due to a vestibular sensory deficiency when the utricular otoliths are beyond their working range because of the change in head position. Since the intact visual and somatosensory control hope widely compensate for the vestibular deficiency, head-extension vertigo is of particular concern only in certain stimulus situations or diseases in which the stabilizing input from the eyes or joint receptors is reduced. Balance training on foam rubber with head extension and closed eyes improved postural-sway activity up to 50% within five days. A daily short-term training effect and a long-term training effect together form a typical exponential sawtooth curve of postural stability over time. After termination of training, learned balance skill exponentially returns to the pretraining values within weeks. The percentage of improvement through training depends on the amount of initial instability. Clinicians should treat ataxia by exposing patients to stimulus situations producing increasing body instability in order to activate sensorimotor rearrangement.

Adolescent↗

PubMedDate not supplied

Spatial dissociation of early and late colour evoked components.

Evoked potentials to the primary colours red, green, yellow and blue were recorded and compared with those evoked by white. The unpatterned 10 degrees X13 degrees stimuli were generated with the aid of a colour monitor. Activity was depicted with 5 electrodes, the central electrode 5 cm above the inion and two on each side 5 and 10 cm apart from the central electrode. With equally bright colour stimuli a previously described early negative colour-dominated component N87 was localized in all subjects at the central occipital electrode while the following positivity P100 was clearly more lateralized to the peripheral electrodes. With half-field stimulation N87 showed a similar--paradoxical--lateralization to the ipsilateral electrodes as has been demonstrated for pattern reversal. The existence and localization of N87 could be confirmed also for blue colours, its amplitude independent of the blue luminance, its latency decreasing for definite additional brightness increments and decrements. The N87 to blue was of the same latency as the N87 components to other colours. N87 is mainly generated foveally and parafoveally, its amplitude saturates with stimuli larger than 6-8 degrees in diameter.

Adolescent↗

PubMedDate not supplied

Can short-latency vestibulospinal reflexes in lower leg muscles be elicited by tapping the head?

A gentle tap on the forehead evoked short-latency motor responses in the sternocleidomastoid muscle, which may be vestibulocollic reflexes with characteristics similar to those elicited by clicks. We tested this paradigm in subjects standing upright, in order to determine the differential effects of taps on the forehead on the patterns and latencies of spinal stretch and vestibulospinal reflexes, which are important for postural control. Taps on the forehead elicited short-latency inhibitory electromyographic responses in both gastrocnemius muscles with a mean latency of 48.3 +/- 3.1 ms (onset) to 98.3 +/- 6.3 ms (end). Taps on the sternum elicited similar responses from the gastrocnemius muscles, indicating that vestibular stimulation is not essential for eliciting these responses. Both responses may play a role in predetermining the strategy for correcting body perturbations. The actual reflex is probably elicited by somatosensory input from the neck, which converges with vestibular input for the multisensory control of posture.

Acceleration↗