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Biomedical subjects

F Thoss

Publications and source records attributed to F Thoss.

At least 19 recordsLinked to original sources
PubMed2003

The human visual threshold depends on direction and strength of a weak magnetic field.

Completing our investigations concerning influences of weak magnetic fields on the visual discrimination threshold, we have investigated 30 subjects (20 female, 10 male) under rotation of the geomagnetic field without change in field strength. We related the thresholds to the values measured in the unchanged field. Comparison with a control experiment shows that correspondence between viewing and field direction results in a significant decrease of the threshold. The significance is lost if the angle between the directions is set to 20 degrees. On the basis of these and our earlier results an attempt is made to give a very simple description of the connection between field direction, field strength, and the change in the visual discrimination threshold.

Dose-Response Relationship, Radiation↗
PubMed2002

The light sensitivity of the human visual system depends on the direction of view.

The near-stable North-South orientation of the natural geomagnetic field provides an ideal basis for navigation. Sailors have used it since ancient times, animals for much longer. Various mechanisms have developed for this purpose. Experiments have pointed to a connection between orientation in the geomagnetic field and light perception. Such observations are supported by theoretical considerations. The underlying interaction should also modulate the light sensitivity of the visual system. Recently we demonstrated the effect of an oscillating field. Here we report the existence of a weak influence of the static field on visual sensitivity in man. By comparison with control experiments, if the directions of view line and field vector coincide the perception threshold of a light stimulus is slightly but significantly increased. This significance is lost if the view line deviates by 10 degrees from the field direction.

Adult↗
PubMed2000

The magnetic field sensitivity of the human visual system shows resonance and compass characteristic.

Orientation in the geomagnetic field is essential for many animal species. As yet, the interaction mechanisms of this weak field with the organisms are understood only incompletely. One mechanism in question is the interaction with the photochemical reaction in the retina. We show that the visual sensitivity of man is influenced by periodic sinusoidal inversion of the vertical component of the geomagnetic field. This effect indicates visual fixation in north-south direction and shows a pronounced resonance at a period duration of 110 s. These findings should be helpful in identifying in detail the mechanisms which are influenced by the geomagnetic field.

Adult↗
PubMed1999

Periodic inversion of the vertical component of the earth's magnetic field influences fluctuations of visual sensitivity in humans.

According to theoretical considerations, the magnetic field of the earth could influence the first steps of light-induced changes in ocular photopigment, an effect that is thought to underlie the magnetic orientation of some animals. To find out whether man could be influenced in this way, we have tested the effect of an artificial fluctuation in the direction of the earth's magnetic field on oscillations of the visual sensitivity in 27 healthy subjects. The resultant spectra show a significant influence of the field fluctuations, indicating that man is sensitive to changes in the direction of the earth's magnetic field.

Adult↗
PubMed1998

Analysis of oscillations of the visual sensitivity.

At the subjective threshold, repeated flash test stimuli are perceived by the observer on only 50% of occasions, since the detectability of a single light stimulus fluctuates with time. For the analysis of these fluctuations we have recorded sequences of positive ("seen") and negative ("not seen") responses, stimulating at 10 sec intervals for 50 min. These records, reflecting the time course of detectability, show periodic fluctuations. The frequencies of these fluctuations have been estimated by autocorrelation and Fourier analysis of the records. For 19 subjects they yielded spectra with preferential period durations between 0.5 and 2, respectively 5 and 15 min in 15 cases, and some spectra are noisy.

Adaptation, Ocular↗
PubMed1997

Influence of an alternating 3 Hz magnetic field with an induction of 0.1 millitesla on chosen parameters of the human occipital EEG.

In 62 volunteers it was studied, whether an alternating 3 Hz magnetic field (induction 0.1 mT) vertically applied to the head over a period of 20 min causes changes in EEG parameters. The study's design was a random crossover controlled, blind one. The field was generated by a Helmholtz coils arrangement. The occipital surface EEGs (O1 and O2) were derived against the left earlobe. Significant differences (two-tailed P < 0.05) between sham and real exposure were found for the relative spectral amplitudes of the theta (3.5-7.5 Hz) and beta band (12.5-25.0 Hz) and the theta/beta ratio. These observations can be interpreted as a more pronounced reduction of alertness under the real field condition compared with the control.

Adolescent↗
PubMed1993

Weak magnetic fields change extinction of a conditioned reaction and daytime melatonin levels in the rat.

Altogether 100 albino rats were conditioned to flee after an acoustic stimulus (1000 Hz). During the following retention period (extinction of the reaction), half of the animals (test group) were exposed to a vertically directed, weak and extremely low-frequency magnetic field (10 Hz, 10(-4) T). Under the field's influence, the animals showed an increased retention of conditioned reactions and had an elevated level of serum melatonin compared with the animals of the control group. These effects disappeared when the investigation was performed in the dark.

Acoustic Stimulation↗
PubMed1990

The influence of a weak artificial magnetic 10 Hz field on the extinction of a conditioned flight reaction in rats.

36 three to four months old albino rats were conditioned to flee after the onset of an acoustic stimulus (1000 Hz). During the period of extinction of the flight reaction half of the animals were exposed to an alternating magnetic field (10 Hz, 0.03 mT peak to peak) for the time of investigation. These animals showed a significantly higher number of flight reactions than the control animals investigated without magnetic field, on the 4th, 5th, and 6th day of exposure (p less than 0.05).

Acoustics↗
PubMed1987

[Development of a test for the objective classification of types of circadian phase].

The authors deal with the question of interindividual differences in the circadian periodicity of man and with the possibility of the classification of circadian phase types resulting from this (morning type, evening type, indifference type). For this purpose on 26 test persons on 3 consecutive days at 9 o'clock and at 17 o'clock, respectively, 11 different vegetatively influenced parameters were measured. The quotients from the averaged 9 o'clock and 17 o'clock-values (Q 9/17) formed the basis for the statistical evaluation (cluster analysis in combination with a discriminance analysis). The result of the discrimination was compared with a subjective subdivision of our test group, based on a questionnaire newly developed by the authors, and yielded a portion of error of 4%. Issuing from this, the authors demonstrate an objective investigation method which shall allow to classify any patients simply, quickly and with high reliability into morning, evening and indifference types, respectively.

Arousal↗
PubMed1986

Visual threshold estimation and its relation to the question: Fechner-law or Stevens-power function.

This investigation was initiated by the apparent rivalry between Fechner-law and Stevens-power function. We used the pupil reaction as on objective measure for the excitation of the visual system within both the threshold and the suprathreshold region. The course of the threshold as a function of adaptation light shows important differences at different field areas. The Weber-law is valid only in the case of large fields (30 degrees) as had been used by Weber himself. At smaller fields the threshold may be described as a power function with exponents of 0.5 at the smallest (0.5 degrees) and about 0.75 at medium sized (5 degrees) fields. In all these experiments the Fechner-hypothesis is suitable automatically because of the constant increment of pupil constriction at the threshold. The validity of the Fechner-hypothesis together with the approximation of the threshold course by power functions lead to Stevens-power functions for the suprathreshold region. The Fechner-law - a logarithmic function - is valid at large fields only. This consideration has been confirmed by our measurements in the suprathreshold sphere.

Biophysical Phenomena↗
PubMed1983

[Effect of an alternating magnetic field on development and extinction of conditioned responses in rats].

This paper deals with the problem whether there is an effect of extremely low frequency electromagnetic fields on simple learning processes. The conditioned reaction upon an electromagnetic fields on simple learning processes. The conditioned reaction upon an acoustic stimulus (1000 Hz) reinforced by an electric painful stimulus was used. During the conditioning and extinction process 28 adult albino rats were put in a 10 Hz, 0,3 G magnetic field. Their learning and extinction behaviour was compared with that of a control group of 28 rats trained under normal laboratory conditions. The extinction schedule differs significantly between the experimental and control group: The extinction develops faster in the experimental group (p less than 0.05). In connection with the results of other authors our findings are discussed as a general amount of adaptability by the influence of the 10 Hz field.

Animals↗
PubMed1981

Applicability of two different lead systems in studies of the electrical activity of the hearts in newborn guinea pigs.

Recent findings of ours from vectorcardiographic studies with the anatomically orthogonal SVEC II system of Schmitt and Simonson on postnatal guinea pigs did not coincide with earlier VCG findings from preparations of isolated guinea pig hearts beating in a homogenous volume conductor. This suggested that in the guinea pig as in the human a more intricately corrected lead system ought to be used. In order to apply to guinea pigs the electrically corrected lead system proposed by Frank in 1956 for clinical use in human electrocardiography, the underlying biophysical assumptions had to be examined. The electrical center of ventricular depolarisation in the guinea pig heart was determined by measurement of cancellation potentials around the thorax and by geometrical construction of different horizontal loops of the image surface. Cancellation coefficients and ventricular dipole locations of guinea pigs of different ages proved to be in the same range as the corresponding human values. Application of the Frank lead system to guinea pigs two days old and older gave vectorcardiographic parameters which corresponded to those obtained from Langendorff heart preparations.

Animals↗
PubMed1980

[Pupillometric studies of the fundamental psychophysical law].

Formulating the correlations bearing both their names, Fecher and Stevens, used aside form Weber's law delta I/I0 = const. hypothetical assumptions about the sensitivity increase at threshold (delta E = const. and delta E/E = const., respectively). closer investigation of the visual system shows that not only these hypotheses will have to be discussed but that Weber's law, too, has to be interpreted more precisely. Measurements of the pupillomotor and sensory threshold yielded delta I/Io alpha = const. with alpha approximately equal to 0.7, consistent with the results of other authors. Irritation with the degree of stimulation, as measured by the variation of the pupillar radius at the dark-adapted eye, is well describable by the power function E = k x In with n approximately equal to 0.35. It is shown that this form is the integrated from of the "generalized Weber's law", where n approximately equal to 1--alpha holds if Fechner's assumption delta E = const. at threshold is true. From the results of Stevens ( n approximately equal to 0.33) and the values of alpha for the visual system. For the other systems, e.g. that of length estimation, the assumption is wrong. To enable uniform description of the varying situation, the more general assumption delta E/E gamma = const. is proposed for the sensitivity increase at threshold; with this approach n = (1--alpha)/(1--gamma) (alpha not equal to 1, gamma not equal to 1) holds.

Adaptation, Ocular↗
PubMed1975

[Possible functional properties of the labyrinth in Brachiosaurus brancai].

The dimensions of the semicircular canals and the respective ampullae of a complete labyrinth caste of Brachiosaurus Brancai were determined. Using the equation of motion and the dimensions of the semicircular canals the behaviour of the endolymph displacement of the Brachiosaurus labyrinth was calculated. The time constants of the system were found to be between the values 4 sec and 13 sec for T1 and 0.2 sec and 0.5 sec for T2. From these results it was concluded, that the head movements of the animal occurred in a range between 0.02 and 0.1 cps.

Animals↗