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Human and Biomimetic Sensors
Published in Patrick F. Dunn, Fundamentals of Sensors for Engineering and Science, 2019
Rotation is sensed via the semicircular canals when the head begins to rotate. The fluid inside it lags because of its inertia. This produces drag on the cupula and causes it to bend in the direction opposite of rotation. As the rotation continues, the cupula returns to its normal position within approximately 30 s. When rotation stops, the fluid continues to move and drag the cupula in the opposite direction. The sensory structures inside the saccule and utricle are somewhat different. Their hair cells are embedded also in a gelatinous mass (the otolith membrane), as shown in Figure 3.12. Crystals called otoliths lay atop this membrane and are bound to proteins on the membrane’s surface. Gravitational displacement of the otoliths causes a movement of the membrane and its hair cells. Linear acceleration and head position changes with respect to the gravitational field are readily sensed. As in the auditory system, movements of a hairs cell’s cilia in either one direction or another causes the cell to either hyperpolarize or depolarize. This, in turn, leads to action potentials generated in the primary afferent neuron that is connected synaptically to the hair cell. Resultant signals travel via different neural pathways to various parts of the brain, including the cerebellum, reticular formation, and thalamus, as well as to the the spine and to nuclei that control eye movement.
Spatial Orientation and Disorientation
Published in Anthony N. Nicholson, The Neurosciences and the Practice of Aviation Medicine, 2017
Groups of head direction cells appear to be networked in that all cells tend to drift by similar amounts in the same direction. When the light is switched on again, the initial preferred firing direction of the cell is restored within 80 milliseconds. This observation raises an interesting parallel with a phenomenon known to aircrew as ‘the leans’ which involves an erroneous sense of roll attitude after manoeuvring in cloud and which is rapidly dispelled once a view of the ground is regained. Thus head direction cells are behaving as a form of internal compass that is maintained not by the Earth’s magnetic field but by visual, locomotor and vestibular cues. The afferent signal from the semicircular canals conveys information about head angular velocity. Cells similarly coded for head angular velocity can be found in brainstem nuclei, in particular the medial vestibular nucleus, the dorsal tegmental nucleus and the lateral mammillary nucleus. Angular velocity of the head derived from vestibular inputs has a significant influence on head direction cell activity. Neurotoxic lesions to the vestibular system abolish the head direction signal in the anterodorsal thalamic nucleus and the posterior subiculum and, in addition, disrupt location-specific firing of place cells in the hippocampus (Taube, 2007).
Spatial Orientation
Published in Pamela S. Tsang, Michael A. Vidulich, Principles and Practice of Aviation Psychology, 2002
Although the semicircular canals primarily detect angular head motions, under some circumstances they also respond to linear acceleration and to gravity. To the extent that the cupulae are not precisely the same density as the surrounding endolymph, they will tend to sink or float slightly under the pull of gravity or when subjected to linear acceleration. In this case, the semicircular canals are also slightly sensitive to head position. The cupula may also be substantially unbalanced by caloric stimulation used in clinical vestibular testing or by alcohol ingestion, as discussed later. Both of these conditions will cause a false sensation of spinning that depends on head position relative to gravity.
Vestibulo-ocular reflex characteristics during unidirectional translational whole-body vibration without head restriction
Published in Ergonomics, 2020
Tomoko Sugawara, Hiroyuki Sakai, Yutaka Hirata
The characteristics of the VOR elicited along or around single-axis head movements are well established. When the head rotates, the semicircular canals detect head angular acceleration and induce counter-rotation of the eyes to stabilise retinal images (Gresty, Hess and Leech 1977; Leigh and Brandt 1993; MacDougall and Moore 2005). In the dark, VOR gains (eye velocity amplitude divided by head angular velocity amplitude) in humans are approximately 0.9 in the yaw rotation (Paige 1994; Tabak et al. 1997; Tweed et al. 1994), 0.7 in the pitch rotation (Goumans et al. 2010; Tweed et al. 1994) and 0.6 in the roll rotation (Goumans et al. 2010; Leigh et al. 1989) (see Figure 1 for the definition of axes and directions). When the head moves translationally, the otolith organs in the inner ear detect head linear acceleration and trigger the VOR, which contributes to ocular stability. Specifically, vertical and lateral accelerations elicit vertical and horizontal VORs, respectively (Baloh et al. 1988; Busettini et al. 1994; Merfeld et al. 2005; Paige 1989), while longitudinal acceleration elicits both vertical and horizontal VORs (Angelaki 1998; Baloh et al. 1988; Paige and Tomko 1991b; Ramat and Zee 2005).
Finite element model of a human lateral semicircular canal of the inner ear
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2019
D. Baumgartner, A. Charpiot, M. Lamy
The human inner ear hosts a fundamental component of the mechanisms regulating balance and maintaining gaze: the vestibular system. It can detect motion thanks to three semicircular canals (SCC), which act as sensors of angular acceleration of the head, using deflections of the cupular diaphragm to generate neural information. This system is often damaged after a head trauma, as a consequence of a traffic accident, a domestic fall or a violent sport activity as well as from blast injury, and this damage causes significant difficulty and reduced quality of life for the accident victim. As the vestibular system is very small, complex to access surgically and breakable when extracted, an accurate understanding of its behaviour has not yet been achieved. One way to improve our knowledge on it is to develop and use analytical models such as Finite Element (FE) analysis tools.
Occupant–vehicle dynamics and the role of the internal model
Published in Vehicle System Dynamics, 2018
The vestibular organs are located in the inner ear and comprise the otoliths and the semicircular canals. These organs have been subject to much study, in humans and in animals. Most mathematical models (usually in the form of frequency response functions) are identified using data from experiments on humans or animals [19]. The otoliths are sensitive to translational acceleration in three axes down to zero frequency. A consequence is that it is difficult for a human to distinguish between a horizontal acceleration and a tilt in the gravity vector. However some driving simulators exploit this characteristic by tilting the motion platform to induce a perception of lateral acceleration. Semicircular canals sense angular velocity in three axes, with a frequency response that is essentially band pass, with roll off at low frequencies ( Hz) such that steady rotation velocity cannot be sensed. This is a potentially advantageous characteristic in driving simulators since it reduces the motion cueing requirements. It is difficult to determine the perception characteristics of the vestibular organs alone because it is difficult to stimulate them without stimulating other modalities; reports of vestibular characteristics should be interpreted with this in mind.