Habituation: A dual-process theory.

The sensation of self-motion is a common visual illusion which allows inferences concerning visual-vestibular interaction. It may be perceived while gazing at moving clouds, streaming water, or when a train moves on the adjacent track in a railway station. This compelling sensation of body movement can even affect postural balance. On first approaching the problem, a psychologic explanation could be suggested in the sense of Helmholtz’s (1896) Urteilstauschung. One might assume that these illusions are inferences based upon the conscious or unconscious assumption of a stable environment, so that when the environment does in fact move, the observer infers that he himself is moving. This interpretation would be consistent with the individual’s past experience as the entire visual surround seldom moves uniformly under natural conditions unless the body moves relative to the earth.

Visual-Vestibular Interaction: Effects on Self-Motion Perception and Postural Control

During natural movement on the earth’s surface, we are seldom aware of vestibular sensations, and when we do become aware of them, they usually signify an unnatural stimulus or an abnormality of vestibular function. With specially contrived conditions of observation, relationships between acceleratory stimuli and vestibular sensations and perceptions can be described quantitatively and qualitatively. These relationships constitute the primary subject matter of this chapter, but to appreciate this material in relation to daily experiences, we must first consider why vestibular sensations do not typically achieve conscious awareness during natural voluntary head and body movement.

Psychophysics of Vestibular Sensation

Contents: Vestibular Nerve and Labyrinthine Disorders.- Central Vestibular Disorders.- Positional Vertigo.- Vascular Vertigo.- Traumatic Vertigo.- Familial Vertigo and Vertigo in Childhood.- Drugs and Vertigo.- Non-Vestibular Vertigo Syndromes.- Psychogenic Vertigo.- Physiological Vertigo.- Subject Index.

Vertigo: Its Multisensory Syndromes

Principal-component analyses were determined on a series of points measured from the dissected bony labyrinth of ten human skulls, resulting in planar equations for each of the six semicircular canals. Following this, angles were calculated between the ipsilateral canal planes, between opposite synergistically acting canal planes and between each canal and the Reid stereotaxic planes. Results indicated that pairs of ipsilateral canals were nearly perpendicular, with the exception of the angle formed between the anterior and horizontal canal (mean = 111 °). Pairs of contralateral synergistic canal planes formed angles of 19° between right and left horizontal canal planes and 23–24° between vertical canal pairs. The horizontal canals formed an angle of 25° with the Reid horizontal plane. Mathematical equations of the semicircular canals were used to predict the optimal head position for rotational and caloric stimulation.This investigation was supported in part by U.S. Public Health Service Grant NS-06658; ...

Planar relationships of the semicircular canals in man.

Five young adult men with normal labyrinthine function were stimulated by a series of graded angular accelerations, during which they carried out particular mental tasks. Each subject was seated at the center of rotation, eyes open, and with head fixed with a bite board so that the lateral canals were in the horizontal plane of rotation. The subject was enclosed in a capsule which provided a totally dark environment, and shielded him from wind currents. Low-level masking noise and vibration prevented detection of extraneous cues related to angular velocity. Ocular nystagmus was analyzed second-by-second and an empiric equation fitted to the data.

Quantification of the Human Nystagmic Response to Angular Acceleration. Prediction Formulae and Nomograph

This experiment evaluated the influence of various types of visual stimulation upon the habituation of nystagmic, oculogyral, and psychophysical responses to angular acceleration. Four groups of 20 young men each were given a series of 16 angular accelerations of 24°/sec2 magnitude and of 10-scc duration. Concomitant visual stimulation, varied between groups from total darkness to full room illumination, was introduced on habituation trials that were interpolated between test trials. Although highly significant decrements for all responses were found with repeated testing, the different visual conditions in no way altered this habituation.

Concomitant Visual Stimulation Does Not Alter Habituation of Nystagmic, Oculogyral Or Psychophysical Responses to Angular Acceleration

Two independent groups of normal human subjects were exposed to a number of long-duration (up to 96 sec), relatively high-intensity (3d`/ sec2-24d`/sec2), constant, angular accelerations. Nystagmic decrements during stimulation were clearly evident. The decrements were initiated at about the same time after stimulus onset (28–32 sec) for all accelerations used. The decrements in the nystagmic responses were compared to related findings for both subjective and electrophysiological responses.

Adaptation to prolonged constant angular acceleration.

A group of cats was exposed to a series of angular accelerations about a vertical rotatory axis with the head tilted so that a synergic pair of vertical canals were in the plane of rotation, and then tested with the lateral canals in the plane of rotation. This group was compared with a second group that received only lateral canal stimulation, and with a third group that received neither lateral nor vertical canal stimulation. It was found that repeated acceleration of the vertical canals does not reduce that nystagmus elicited with the lateral canals accelerated in the plane of rotation.

Repeated vertical semicircular canal stimulation does not habituate horizontal nystagmus in cat.

: Sixteen young adult men were deprived of sleep for a period of 24 hours in an attempt to assess possible interactions between sleep mechanisms and the vestibular system. Ss were given a pre- and post-test consisting of trials at angular accelerations of 8 degrees/sec sq and 24 degrees/sec sq. Following sleep deprivation, Ss showed a significant increase in fast-phase frequency at 24 degrees/sec sq, and a nonsignificant increment at 8 degrees/sec sq. Slow-phase output reflected a significant decrement at 8 degrees/sec sq, but no significant decrement at 24 degrees/sec sq. Subjective latency estimates of stimulus onset showed no significant changes for either 8 degrees or 24 degrees/sec sq. Discussion centers around possible physiological mechanisms related to sleep and vestibular responses. (Author)

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James H. Brown

Papers

Quantification of the Human Nystagmic Response to Angular Acceleration. Prediction Formulae and Nomograph

Concomitant Visual Stimulation Does Not Alter Habituation of Nystagmic, Oculogyral Or Psychophysical Responses to Angular Acceleration

Adaptation to prolonged constant angular acceleration.

Repeated vertical semicircular canal stimulation does not habituate horizontal nystagmus in cat.

Effects of Sleep Deprivation on the Vestibulo-Ocular Reflex