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Biomedical subjects

H Mittelstaedt

Publications and source records attributed to H Mittelstaedt.

27 records · Page 2Linked to original sources
PubMed1989

How to explain a constant subjective vertical at constant high speed rotation about an earth-horizontal axis.

When rotated in darkness about an earth-horizontal axis at speeds above 0.2-0.5 Hz, subjects, instead of feeling rotated, experience a constant (though extrapersonally diverse) position in space and a constant visual vertical (SV). Computer simulation shows that this phenomenon cannot be explained by the extant models of Mayne (1) and Ormsby (2) about the interaction of otoliths and semicircular canals. It follows, however, from a static theory of the SV (3) if, as in the presently proposed dynamic model, the otolith afference is processed by a low-pass filter. At high speed rotation this filter can only be passed by the force-independent, temporally invariant components of the otolith information. Such force-independent components are bound to result from biassed resting discharges, and have previously been shown to affect the SV and the self-adopted horizontal position. The interaction of otoliths and canals proposed by the model does provide a veridical vertical in a working range of angular frequencies and hence a basis for inertial navigation.

Acceleration↗
PubMedDate not supplied

The influence of otoliths and somatic graviceptors on angular velocity estimation.

In three psychophysical experiments subjects (Ss), blindfolded and earphoned with white noise, estimated their angular speed A) after brief acceleration to constant centric or eccentric rotation, and B) after deceleration to a full stop. Ss either indicated whenever they were rotated through 180 degrees, or manipulated the objective velocity such that the subjective one stayed constant. With Ss in an earth-vertical attitude, subjective speed declined exponentially with a time constant that depended on eccentricity in paradigm A, but not in B. The time constant depended linearly on the amount of the centrifugal force, but not on its direction. Thus, centrifugal force has an enhancing effect on perceived angular speed. The relevant sense organs were identified with Ss in a radial, earth-horizontal attitude. The enhancing effect was minimal when the axis of rotation was caudal of the otoliths, indicating an effect of graviceptors in the trunk. This effect, just as the effect of recently discovered truncal graviceptors on the perception of posture, turned out to depend on leg position: The minimum of the enhancing effect shifted from about 30 cm to about 60 cm caudal of the otoliths, when leg position changed from flexed to extended. It is concluded that the centrifugal force, measured by otoliths and truncal graviceptors, serves to provide information on angular velocity at eccentric rotation, at least as long as the output of the velocity storage is not yet zero.

Gravitation↗
PubMedDate not supplied

Interaction of eye-, head-, and trunk-bound information in spatial perception and control.

This article reviews the author's investigations on the perception and control of spatial relations if the carriers of the relevant sense organs are mobile and controlled independently of each other. In the dragonfly, head rotation is controlled by the head's inertia, as well as by cervicocollic, optokinetic, and dorsal light reflexes and, in turn, controls trunk rotation by means of neck reflexes on the wings. In humans, invariance of head-referenced visual direction under eye-to-head rotation is attained by feedforward of an efference copy. In the pigeon, invariance of responses to trunk tilt under head-to-trunk rotation is, in flight, achieved by feedforward of head-to-trunk information yielded by neck receptors. But in standing or walking, this is accomplished by means of gravity sense organs in the trunk. Such organs are also shown to exist in the human trunk by means of experiments on a sled centrifuge. From tests with paraplegic and neuromectomized subjects, it is concluded that truncal graviception 1) is not influenced by mechanoreceptors in the legs, the skin, and between the vertebrae, but 2) is affected by at least two afferent inputs, one originating in the kidneys, another in the tissues that support the large blood vessels against the gravitational load. These conclusions are corroborated by experiments with bilaterally nephrectomized subjects and by means of positive air pressure to the legs, respectively. Recent results under application of positive and negative air pressure to the entire lower body indicate that yet another source of somatic graviception may exist, for example, one that exploits the hydrostatics of blood pressure or the inertia of the mass of the abdominal viscera.

Animals↗