Horst Mittelstaedt

Das Reafferenzprinzip. Wechselwirkungen zwischen Zentralnervensystem und Periphase

~) Wenn man den Strum im Kondensatorkreis um-nittelbar dureh die Spulen Sp~ und Sp~ hindurchsehickt, wird die Phase der Ablenkung des Kathodenstrahlbiindels zur Anfaehung ungeeignet. Die Absicht dieser Mitteilung ist durchaus nicht, dem erfolgreichen Erfinder der Rfickkoppelung die Priorit~it streitig zu machen. Vielleieht kann sie aber einen bescheidenen Beitrag liefern z u r Charakterisierung yon FERDINAND BRAUN als Physiker und zur Erinnerung an ihn in diesem Jahr, in dem sich sein Geburtstag zum t00. Male j~thrt. Mitteilung aus dem Deutschen Museum M~inchen.

Homing by path integration

The paper presents experimental evidence for homing by path integration in a bird. Using a mammalian model case, the essentials of a cybernetical theory of this type of navigation are developed. As a consequence of its application to the extant data on geese, the necessary information about the translatory component of the animal’s movement along its path appears to be provided by the visual system, viz. the translatory component of the visual flow, whereas the rotatory information must (also) have non-visual sources, e.g. the semicircular canals or the magnetic field.

Somatic versus Vestibular Gravity Reception in Man

In order to assess the effect of extravestibular gravity receptors on perception and control of body position against that of the otoliths, the subject (S) is exposed to gravitoinertial forces along the spinal (Z) axis on a tiltable board and on a sled centrifuge. It turns out that (1) both effects, on average, are equally strong, although with considerable variance between Ss; (2) the centroid of the mass(es) governing the somatic receptors lies near the centroid of the body; and (3) somatic gravity reception contains two distinctly different systems. Both appear unimpaired in paraplegic Ss with total bilateral sensory loss (TSL) from the 5th to the 1st lumbar spinal segment. One, the truncal system, is eliminated with TSL from the 11th thoracic segment upwards. Yet another is still functioning with TSL up to and including the 6th cervical segment, with the same effectiveness throughout this range. Hence it must be mediated by vagal or, less likely, sympathetic afference, that is, probably, by the influence of gravity on the cardiovascular system. That the afference of the truncal system appears to enter the cord at the last two thoracic segments supports earlier conjectures about a supererogatory static function of the kidneys. In fact, on the tiltable board, 7 bilaterally nephrectomized Ss behaved like paraplegics with TSL between T11 and C6, yet differed significantly in the predicted direction from the normal controls.

Idiothetic navigation in humans: estimation of path length

Abstract. When vision is excluded humans are still able to walk back to a starting point or to a previously seen target. This performance may be mediated by path integration, based on information about movement with respect to the ground or to inertial space, that is, on substratal or inertial idiothetic cues. We intend to unravel whether, and how accurately, these two inputs act and interact on the translatory component of this navigation performance. Subjects were asked 1) to reproduce a path they had walked, and 2) to indicate the location of a target they had seen before being blindfolded by (i) walking there, (ii) treading a motor-driven conveyor belt until they imagine they are there, and (iii) reporting, while being driven in a trolley, when they seem to pass the target. The estimation of path length turns out to vary as a function of walking velocity, step length, and step rate. The estimate becomes virtually veridical when subjects walk at their normal pace, but it overshoots at lower and undershoots at higher values of these variables. Veridicality at near normal speeds is also found with passive transport (iii), but with a reverse dependence on velocity. It is concluded that in these paradigms path control and perception are mediated by an open-loop performance of the underlying path integration system, calibrated in such a way as to yield veridical estimates during normal walking. Either inertial or substratal idiothetic information is sufficient for this performance. However, the quantitative relations found argue in favor of the hypothesis that substratal idiothetic information predominates when both are available. In spite of its limitations the capability shown here may serve as an essential constituent of navigation by path integration in humans.

The role of the otoliths in perception of the vertical and in path integration

Abstract: The role of the otoliths in essential performances of human orientation is analyzed. The following interactions of the otoliths are considered:

The subjective vertical as a function of visual and extraretinal cues

Abstract This contribution tries to generalize a theory about the effect of the gravity and idiotropic vectors on the subjective vertical (SV) by encompassing the influence of ‘verticalizing’ visual patterns. Such patterns are first experimentally shown to form a resultant with, rather than to suppress, the gravito-idiotropic vector. By varying the position of the visual panorama, its effect on this resultant turns out to be determined by sine functions of the angle between the SV and the upright axis of the panorama, and of the angles multiples (named ‘SV-function’). The peculiar features of the visual influence, and its seemingly incompatible effects in earlier experiments on tilt illusions are shown to result from qualitative and quantitative properties of the SV-function. The underlying information processing structure — after experimental falsification of two feedforward variants — is envisaged to contain a central nervous component generator, which is controlled by internal feedback of its own output, after the latter is cross-multiplied with circular Fourier components selected from a central nervous representation of the retinal pattern. Lastly, a weighting procedure is suggested which may extract the required even number circular Fourier components from arrays of cortical neurons of known properties.

Analytical cybernetics of spider navigation

The navigation of the funnel web spider is a complex behavioral performance: it depends on the animal’s motivation, which in turn changes seasonally, diurnally, and by dint of various vicissitudes including the consequences of its own success of failure; it uses allothetic sources of spatial information such as the overall light distribution, specifically the sun and the polarization pattern of the sky, the structure and the inclination of the web, as well as idiothetic sources such as stored records of the animal’s own movements provided by proprioceptors or efference copies (see also Gorner and Claas, Chap. XIV, this Vol.); it employs large arrays of receptors and effectors connected by a central nervous organization which might lead to perfect navigation, were it not for the everpresent influence of noise at all levels of the system.

Perception of spatial orientation in microgravity

Experiments during space and parabolic flights have shown that human spatial orientation in microgravity differs to a significant extent from its performance on earth. Due to the missing reference of gravitational force, unusual perceptual phenomena are observed, from inversion illusions to errors of perceived motion and position with respect to the spacecraft. This article gives an overview of results collected from space missions and parabolic flight campaigns, and proposes new lines of research about the perceptual phenomena of spatial orientation in microgravity. It is shown that most of the disorientation phenomena can be explained by the existence of an internal estimate of the gravitational vertical. In microgravity it is still maintained, but incorrectly updated, and thus alters the processing of sensory information in the central nervous system. This in turn leads to the observed illusions, and probably also facilitates space motion sickness.

Evaluation of retinal orientation and gaze direction in the perception of the vertical

The orientation of the median plane of the eye with respect to the head varies with gaze direction according to Listings Law. The subjective vertical (SV), however, is known to be only partially affected by these involuntary variations of eye orientation. In order to learn more about the compensatory process underlying this finding, six normal-sighted young subjects were tested monocularly and binocularly in eight directions of gaze. The results show that: (1) the SVs, determined monocularly for both eyes, fall on corresponding retinal meridians, the binocular SV-settings generally lie between the monocular ones; (2) the tilt of the SV is not linearly related to the tilt angle of the median plane of the eye, as hitherto assumed. On theoretical considerations, the dependence of ocular tilt on gaze direction may be decomposed into three components, which are all treated differently in the compensation process. We interpret these results in the following way: the SV is determined from the sensorially fused image of both eyes and the tilts of the eyes are accounted for by an extra-retinal signal which is common to both eyes. The characteristics of the compensation mechanism may be explained by an extra-retinal signal which relies on information about gaze direction and Listings Law. Such a signal might be derived from an efference copy of gaze direction commands.

Triple-loop model of path control by head direction and place cells.

Abstract. Arthropods as well as mammals are able to return straight home after a random search excursion under conditions that are designed to exclude all external cues. After a brief clarification of the terminology, two principal systems of information processing that can achieve this performance are introduced and analysed: Polar versus Cartesian path integration. The different demands and achievements of the two systems are confronted with neurophysiological findings on the functioning of the hippocampus, and with a recent comprehensive model of how the hippocampal place cells perform path integration. To connect the neurophysiological findings with the behavior of the animal, a new model is developed. It achieves three functionally diverse performances: maintenance and control of a compass direction, navigation by path integration, and formation of goals by connecting non-spatial features with their location. This is done by three interconnected feedback loops, set by a common reference variable. Their information-processing structure enables the animal not only to home but also to go straight from any stored goal to any other, without explicit representation of the distance between them, and without a topological arrangement of the store. The model explains behaviors not yet understood and predicts still undiscovered performances. Because it allows the isolation of orienting from storing functions yet also shows how they can be connected, the model may help to reconcile conflicting views on the function of the hippocampus.