Spatial disorientation

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Spatial disorientation is the inability to determine position or relative motion, commonly occurring during periods of challenging visibility, since vision is the dominant sense for orientation. The auditory system, vestibular system (within the inner ear), and proprioceptive system (sensory receptors located in the skin, muscles, tendons and joints) collectively work to coordinate movement with balance, and can also create illusory nonvisual sensations, resulting in spatial disorientation in the absence of strong visual cues.

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In aviation, spatial disorientation can result in improper perception of the attitude of the aircraft, referring to the orientation of the aircraft relative to the horizon. If a pilot relies on this improper perception, this can result in inadvertent turning, ascending or descending. For aviators, proper recognition of aircraft attitude is most critical at night or in poor weather, when there is no visible horizon; in these conditions, aviators may determine aircraft attitude by reference to an attitude indicator. Spatial disorientation can occur in other situations where visibility is reduced, such as diving operations.

Flight safety, history, and statistics

Equilibrium test being administered to prospective pilot, via Barany chair Barany Chair equilibrium test.jpg
Equilibrium test being administered to prospective pilot, via Bárány chair

Spatial orientation in flight is difficult to achieve because numerous sensory stimuli (visual, vestibular, and proprioceptive) vary in magnitude, direction, and frequency. Any differences or discrepancies between visual, vestibular, and proprioceptive sensory inputs result in a sensory mismatch that can produce illusions and lead to spatial disorientation. The visual sense is considered to be the largest contributor to orientation. [1] :4

While testing an early turn and slip indicator devised by his friend Elmer Sperry in 1918, United States Army Air Corps pilot William Ocker entered a graveyard spiral while flying through clouds without visual references; the turn indicator showed he was in a turn, but his senses told him he was in level flight. Emerging from the clouds, Ocker was able to recover from the dive. [2] In 1926, Ocker was subjected to a Bárány chair equilibrium test by Dr. David A. Myers at Crissy Field; the resulting duplication of the somatogyral illusion he had experienced and a subsequent re-test, which he passed using the turn indicator, [3] led him to develop and champion instrumented flight. [4] Sperry would go on to invent the gyrocompass and attitude indicator, both of which were being tested by 1930. [5] :8 With Lt. Carl Crane, Ocker published the instructional text Blind Flying in Theory and Practice in 1932. [4] Influential advocates of instrumented flight training included Albert Hegenberger and Jimmy Doolittle. [5] :8

In 1965, the Federal Aviation Agency of the United States issued Advisory Circular AC 60-4, warning pilots about the hazards of spatial disorientation, which may result from operation under visual flight rules in conditions of marginal visibility. [6] A new version of the advisory was issued in 1983 as AC 60-4A, defining spatial disorientation as "the inability to tell which way is 'up.'" [7]

Statistics show that between 5% and 10% of all general aviation accidents can be attributed to spatial disorientation, 90% of which are fatal. [8] Spatial-D and G-force induced loss of consciousness (g-LOC) are two of the most common causes of death from human factors in military aviation. [9] A study on the prevalence of spatial disorientation incidents concluded that "if a pilot flies long enough ... there is no chance that he/she will escape experiencing at least one episode of [spatial disorientation]. Looked at another way, pilots can be considered to be in one of two groups; those who have been disorientated, and those who will be." [1] :2

Physiology

There are four physiologic systems that interact to allow humans to orient themselves in space. Vision is the dominant sense for orientation, but the vestibular system, proprioceptive system and auditory system also play a role.[ citation needed ]

Spatial orientation (the inverse being spatial disorientation, aka spatial-D) is the ability to maintain body orientation and posture in relation to the surrounding environment (physical space) at rest and during motion. Humans have evolved to maintain spatial orientation on the ground. Good spatial orientation on the ground relies on the use of visual, auditory, vestibular, and proprioceptive sensory information. Changes in linear acceleration, angular acceleration, and gravity are detected by the vestibular system and the proprioceptive receptors, and then compared in the brain with visual information.[ citation needed ]

The three-dimensional environment of flight is unfamiliar to the human body, creating sensory conflicts and illusions that make spatial orientation difficult and sometimes impossible to achieve. The result of these various visual and nonvisual illusions is spatial disorientation. [10] [9] [11] Various models have been developed to yield quantitative predictions of disorientation associated with known aircraft accelerations. [12]

The vestibular system and sensory illusions

Inner ear Blausen 0329 EarAnatomy InternalEar.png
Inner ear

The vestibular system detects linear and angular (rotational) acceleration using specialized organs in the inner ear. Linear accelerations are detected by the otolith organs, while angular accelerations are detected by the semicircular canals.

Misleading sensations

Without a visual reference or cues, such as a visible horizon, humans will rely on non-visual senses to establish their sense of motion and equilibrium. During the abnormal acceleratory environment of flight, the vestibular and proprioceptive systems can be misled, resulting in spatial disorientation. When an aircraft is maneuvering, inertial forces can be created by changes in vehicle speed (linear acceleration) and/or changes in direction (rotational acceleration and centrifugal force), resulting in perceptual misjudgment of the vertical, as the combined forces of gravity and inertia do not align with what the vestibular system assumes is the vertical direction of gravity (towards the center of the Earth).

Under ideal conditions, visual cues will provide sufficient information to override illusory vestibular inputs, but at night or in poor weather, visual inputs can be overwhelmed by these illusory nonvisual sensations, resulting in spatial disorientation. Low visibility flight conditions include night, [6] over water or other monotonous/featureless terrain that blends into the sky, [6] white-out weather, [6] or inadvertent entry into instrument meteorological conditions after flying into fog or clouds.

Lift (L) and weight/gravity (w) forces acting on an aircraft making a banked or coordinated turn Load factor and the g-force in turn.svg
Lift (L) and weight/gravity (w) forces acting on an aircraft making a banked or coordinated turn

For example, in an aircraft that is making a coordinated (banked) turn, no matter how steep, occupants will have little or no sensation of being tilted in the air unless the horizon is visible, as the combined forces of lift and gravity are felt as pressing the occupant into the seat without a lateral force sliding them to either side. [13] Similarly, it is possible to gradually climb or descend without a noticeable change in pressure against the seat. In some aircraft, it is possible to execute a loop without pulling negative g-forces so that, without visual reference, the pilot could be upside down without being aware of it.[ citation needed ] A gradual change in any direction of movement may not be strong enough to activate the vestibular system, so the pilot may not realize that the aircraft is accelerating, decelerating, or banking.

Standard set of flight instruments, including attitude indicator (top center) and turn and slip indicator (bottom left) BASIC Flight instruments Improved.svg
Standard set of flight instruments, including attitude indicator (top center) and turn and slip indicator (bottom left)

Gyroscopic flight instruments such as the attitude indicator (artificial horizon) and the turn and slip indicator are designed to provide information to counteract misleading sensations from the non-visual senses.

Otoliths and somatogravic illusions

Two otolith organs, the saccule and utricle, are located in each ear and are set at right angles to each other. The utricle detects changes in linear acceleration in the horizontal plane, while the saccule detects linear accelerations in the vertical plane; humans have evolved to assume the vertical acceleration is caused by gravity. However, the saccule and utricle can provide misleading sensory perception when gravity is not limited to the vertical plane, or when vehicle speeds and accelerations result in inertial forces comparable to the force of gravity, as the otoliths only detect acceleration, and cannot distinguish inertial forces from the force of gravity. [8] Some examples of this include the inertial forces experienced during a vertical take-off in a helicopter or following the sudden opening of a parachute after a free fall.[ citation needed ]

Illusions caused by the otolith organs are called somatogravic illusions and include the Inversion, Head-Up, and Head-Down Illusions. The Inversion Illusion results from a steep ascent followed by a sudden return to level flight; the resulting relative increase in forward speed produces an illusion the aircraft is inverted. [8] The Head-Up and Head-Down illusions are similar, involving sudden linear acceleration (Head-Up) or deceleration (Head-Down), leading to a misperception the nose of the aircraft is pitching up (Head-Up) or down (Head-Down); the aviator could be fooled into pitching the nose down (Head-Up) or up (Head-Down) in response, leading to a crash or a stall, respectively. [8]

Typically, the Head-Up illusion occurs during take-off, as a strong linear acceleration is used to generate lift over the wing and flaps. Without a visual reference, the pilot may assume from the vestibular system the nose has pitched up and command a dive; if this occurs during take-off, the aircraft may not have sufficient altitude to recover before crashing into the ground. [1] :7

Semicircular canals and somatogyral illusions

Inner ear with semicircular canals shown, likening them to the roll, pitch and yaw axis of an aircraft Innernvestib.jpg
Inner ear with semicircular canals shown, likening them to the roll, pitch and yaw axis of an aircraft

In addition, the inner ear contains rotational accelerometers, known as the semicircular canals, which provide information to the lower brain on rotational accelerations in the pitch, roll and yaw axes. Changes in angular velocity are detected from the relative motion between the fluid in the canals and the canal itself, which is fixed to the head; because of inertia, the fluid in the canals tends to lag when the head moves, signaling a rotational acceleration. However, semicircular canal output ceases after prolonged rotation (beyond 15–20 s) as the fluid has now been entrained into motion through friction, matching the motion of the head. If the rotation is then stopped, the perceived motion signal from the inner ear indicates the aviator is now turning in the opposite direction from actual travel, as the fluid continues to move while the canal has stopped. [8] In addition, the inertia of the fluid means the detection threshold of rotational acceleration is limited to approximately 2°/sec2; angular accelerations below this value cannot be detected. [1] :5 Specific common somatogyral illusions induced by the semicircular canals are the Leans, Graveyard Spin, Graveyard Spiral, and Coriolis.

If the aircraft enters an unnoticed, prolonged turn gradually, then suddenly returns to level flight, the leans may result. The gradual turn sets the fluid into the semicircular canals into motion, and rotational acceleration of two degrees per second (or less) cannot be detected. Once the aircraft suddenly returns to level flight, the continued fluid motion gives the sensation the aircraft is banking in the opposite direction of the turn that just ended; the aviator may attempt to correct the misperception of the vertical by banking into the original turn. [8] The leans is considered the most common form of spatial disorientation. [1] :9

Graveyard spiral and graveyard spin FAA PHAK 2008 Fig 16-5 Graveyard spiral.png
Graveyard spiral and graveyard spin

The graveyard spiral and graveyard spin are both caused by the acclimation of the semicircular canals to prolonged rotation; after a banked turn (in the case of the graveyard spiral) or spin (for the graveyard spin) of approximately 20 seconds, the fluid in the semicircular canals has been entrained into motion by friction, and the vestibular system no longer perceives a rotational acceleration. If the aviator then ends the turn or spin and returns to level flight, the continued motion of the fluid will cause a sensation the aircraft is turning or spinning in the opposite direction, and the pilot may re-enter the original turn or spin inadvertently; the aviator may not recognize the illusion before the aircraft loses too much altitude, resulting in a collision with terrain [8] or the g-forces on the aircraft may exceed the structural strength of the airframe, resulting in catastrophic failure. One of the most infamous mishaps in aviation history involving the graveyard spiral is the crash involving John F. Kennedy Jr. in 1999. [14]

Once an aircraft enters conditions under which the pilot cannot see a distinct visual horizon, the drift in the inner ear continues uncorrected. Errors in the perceived rate of turn about any axis can build up at a rate of 0.2 to 0.3 degrees per second.[ citation needed ] If the pilot is not proficient in the use of gyroscopic flight instruments, these errors will build up to a point that control of the aircraft is lost, usually in a steep, diving turn known as a graveyard spiral. During the entire time, leading up to and well into the maneuver, the pilot remains unaware of the turning, believing that the aircraft is maintaining straight flight. [15] :125

In a 1954 study (180 – Degree Turn Experiment), the University of Illinois Institute of Aviation found that 19 out of 20 non-instrument-rated subject pilots went into a graveyard spiral soon after entering simulated instrument conditions. The 20th pilot also lost control of his aircraft, but in another maneuver. The average time between onset of instrument conditions and loss of control was 178 seconds. [16]

Spatial disorientation can also affect instrument-rated pilots in certain conditions. A powerful tumbling sensation (vertigo) can result if the pilot moves his or her head too much during instrument flight. This is called the Coriolis illusion. Because the semicircular canals are set in three different axes of rotation, if the aviator suddenly moves their head during a rotational acceleration, one canal may abruptly start to detect an angular acceleration while another ceases, resulting in a tumbling sensation. [1] :9

Visual illusions

Even with good visibility, misleading visual inputs such as sloping cloud decks, unfamiliar runway grades, or false horizons can also form optical illusions, resulting in the pilot misjudging the vertical orientation, aircraft speed or altitude, and/or distance and depth perception; these could even combine with nonvisual illusions from the vestibular and proprioceptive systems to produce an even more powerful illusion. [17]

Examples

Selected list of aviation accidents attributed to spatial disorientation
DateLocationAccident/FlightNotes & Refs.
Feb 3, 1959 Clear Lake, Iowa, USA The Day the Music Died Crash of Beechcraft Bonanza that killed Buddy Holly, Ritchie Valens, and "The Big Bopper" J. P. Richardson; pilot was not qualified for instrumented flight but took off into deteriorating weather because the passengers were important. Forensic evidence showed the aircraft was in a steep right bank (90°), nose-down attitude at 3,000 ft/min (910 m/min) when it crashed. [18]
Mar 5, 1963 Camden, Tennessee, USA 1963 Camden PA-24 crash Four deaths, including singer Patsy Cline.
Jul 31, 1964Brentwood, Nashville, Tennessee, USA1964 Beechcraft Debonair crashIt is believed[ according to whom? ] that singer Jim Reeves was suffering from spatial disorientation when his Beechcraft aircraft crashed in the Brentwood area of Nashville, Tennessee, during a violent thunderstorm on July 31, 1964, claiming the lives of both Reeves and his pianist Dean Manuel.
Jan 1, 1978 Arabian Sea, near Santacruz Airport, Bombay, India Air India Flight 855
Oct 21, 1978 Bass Strait, Australia Disappearance of Frederick Valentich
Jun 6, 1992 Darién Gap, near Tucutí, Panama Copa Airlines Flight 201
Jul 16, 1999 Atlantic Ocean, off the west coast of Martha's Vineyard, Massachusetts, USA John F. Kennedy Jr. plane crash Crash occurred during a night flight over water near Martha's Vineyard. Subsequent investigation pointed to spatial disorientation as a probable cause of the accident. [19] Because of pilot John F. Kennedy Jr.'s fame, the cause of the crash led to extensive reporting of spatial disorientation in the press in 1999. [14]
Jan 10, 2000 Niederhasli, Switzerland Crossair Flight 498
Aug 23, 2000 Persian Gulf, near Bahrain International Airport, Bahrain Gulf Air Flight 072
Oct 16, 2000 Hillsboro, Missouri, USA2000 Cessna 335 crashLeft-side attitude indicator failed and pilot kept turning his head to cross-check the right-side (co-pilot position) attitude indicator, leading to spatial disorientation; [20] the crash killed Missouri Governor Mel Carnahan. [21]
Jan 3, 2004 Red Sea, near Sharm El Sheikh International Airport, Egypt Flash Airlines Flight 604 Disputed cause: possible pilot error (from spatial disorientation) or mechanical/software malfunctions
Mar 15, 2005near Campbeltown, Argyll, Scotland 2005 Loganair Islander accident
Jan 1, 2007 Makassar Strait off Majene, Sulawesi, Indonesia Adam Air Flight 574 Due to the crew's focus on troubleshooting a problem with the INS, they had disconnected the autopilot without noticing and did not realize that they were in a descent until recovery was improbable. The G forces on the aircraft were stressing the hull of the aircraft and further disoriented the crew until the aircraft broke up in mid-air.
May 5, 2007 Douala International Airport, Cameroon Kenya Airways Flight 507
Nov 30, 2007Türbetepe, Keçiborlu, Isparta Province, Turkey Atlasjet Flight 4203
Sep 14, 2008 Perm, Russia Aeroflot Flight 821
Jun 1, 2009over Atlantic Ocean, near waypoint TASIL Air France Flight 447
May 12, 2010 Tripoli International Airport, Libya Afriqiyah Airways Flight 771
Aug 24, 2010near Shikharpur, Nepal Agni Air Flight 101
Oct 1, 2012Upper Kandanga, Queensland, Australia 2012 Queensland DH.84 Dragon crash Vintage aircraft named Riama
Mar 19, 2016 Rostov-on-Don, Russia Flydubai Flight 981
May 12, 2018near Centennial Airport, Colorado, USACirrus SR22 crashFederal investigators determined that pilot disorientation in difficult weather conditions likely was the cause of a fatal small plane crash. [22] [23]
Feb 23, 2019 Trinity Bay, Texas, USA Atlas Air Flight 3591 The crash of the Boeing 767 cargo jet was caused by the inappropriate response by the first officer as the pilot flying to an inadvertent activation of the plane's go-around mode at a high altitude (6,200 feet), which led to his spatial disorientation. [24] [25]
Apr 9, 2019near Aomori Prefecture, Japan2019 JASDF F-35 crashFirst crash of an F-35A; [26] pilot descended rapidly during a simultaneous left-hand turn. [27] [28]
Jan 26, 2020 Calabasas, California, USA 2020 Calabasas helicopter crash Ara Zobayan, the helicopter pilot in the fatal accident that killed Kobe Bryant along with his daughter Gianna and six others on January 26, 2020, was determined to have likely experienced spatial disorientation according to NTSB investigation. [29]

See also

Related Research Articles

<span class="mw-page-title-main">Inner ear</span> Innermost part of the vertebrate ear

The inner ear is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:

<span class="mw-page-title-main">Motion sickness</span> Nausea caused by motion or perceived motion

Motion sickness occurs due to a difference between actual and expected motion. Symptoms commonly include nausea, vomiting, cold sweat, headache, dizziness, tiredness, loss of appetite, and increased salivation. Complications may rarely include dehydration, electrolyte problems, or a lower esophageal tear.

<span class="mw-page-title-main">Sense of balance</span> Physiological sense regarding posture

The sense of balance or equilibrioception is the perception of balance and spatial orientation. It helps prevent humans and nonhuman animals from falling over when standing or moving. Equilibrioception is the result of a number of sensory systems working together; the eyes, the inner ears, and the body's sense of where it is in space (proprioception) ideally need to be intact.

<span class="mw-page-title-main">Semicircular canals</span> Organ located in innermost part of ear

The semicircular canals are three semicircular interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the lateral, anterior and posterior semicircular canals. They are the part of the bony labyrinth, a periosteum-lined cavity on the petrous part of the temporal bone filled with perilymph. 

<span class="mw-page-title-main">Vestibular system</span> Sensory system that facilitates body balance

The vestibular system, in vertebrates, is a sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating movement with balance. Together with the cochlea, a part of the auditory system, it constitutes the labyrinth of the inner ear in most mammals.

<span class="mw-page-title-main">Space adaptation syndrome</span> Condition caused by weightlessness

Space adaptation syndrome (SAS) or space sickness is a condition experienced by as many as half of all space travelers during their adaptation to weightlessness once in orbit. It is the opposite of terrestrial motion sickness since it occurs when the environment and the person appear visually to be in motion relative to one another even though there is no corresponding sensation of bodily movement originating from the vestibular system.

<span class="mw-page-title-main">Instrument meteorological conditions</span> Flight category requiring pilots to fly with instruments rather than sight

In aviation, instrument meteorological conditions (IMC) are weather conditions that require pilots to fly primarily by reference to flight instruments, and therefore under instrument flight rules (IFR), as opposed to flying by outside visual references under visual flight rules (VFR). Typically, this means flying in cloud or poor weather, where little or nothing can be seen or recognised when looking out of the window. Simulated IMC can be achieved for training purposes by wearing view-limiting devices, which restrict outside vision and force the trainee to rely on instrument indications only.

<span class="mw-page-title-main">Motion simulator</span> Type of mechanism

A motion simulator or motion platform is a mechanism that creates the feelings of being in a real motion environment. In a simulator, the movement is synchronised with a visual display of the outside world (OTW) scene. Motion platforms can provide movement in all of the six degrees of freedom (DOF) that can be experienced by an object that is free to move, such as an aircraft or spacecraft:. These are the three rotational degrees of freedom and three translational or linear degrees of freedom.

<span class="mw-page-title-main">Bárány chair</span> Device used for aerospace physiology training

The Barany chair or Bárány chair is a device used for aerospace physiology training, particularly for student pilots.

<span class="mw-page-title-main">Vestibular nerve</span> Branch of the vestibulocochlear nerve

The vestibular nerve is one of the two branches of the vestibulocochlear nerve. In humans the vestibular nerve transmits sensory information transmitted by vestibular hair cells located in the two otolith organs and the three semicircular canals via the vestibular ganglion of Scarpa. Information from the otolith organs reflects gravity and linear accelerations of the head. Information from the semicircular canals reflects rotational movement of the head. Both are necessary for the sensation of body position and gaze stability in relation to a moving environment.

<span class="mw-page-title-main">Sensory illusions in aviation</span> Misjudgment of true orientation by pilots

Human senses are not naturally geared for the in-flight environment. Pilots may experience disorientation and loss of perspective, creating illusions that range from false horizons to sensory conflict with instrument readings or the misjudging of altitude over water.

<span class="mw-page-title-main">Ampullary cupula</span>

The ampullary cupula, or cupula, is a structure in the vestibular system, providing the sense of spatial orientation.

<span class="mw-page-title-main">Otolithic membrane</span>

The otolithic membrane is a fibrous structure located in the vestibular system of the inner ear. It plays a critical role in the brain's interpretation of equilibrium. The membrane serves to determine if the body or the head is tilted, in addition to the linear acceleration of the body. The linear acceleration could be in the horizontal direction as in a moving car or vertical acceleration such as that felt when an elevator moves up or down.

<span class="mw-page-title-main">Graveyard spiral</span> Spiral dive entered by a pilot due to spatial disorientation

In aviation, a graveyard spiral is a type of dangerous spiral dive entered into accidentally by a pilot who is not trained or not proficient in flying in instrument meteorological conditions (IMC). Other names for this phenomenon include suicide spiral, deadly spiral, death spiral and vicious spiral.

<span class="mw-page-title-main">Acceleration onset cueing</span>

Acceleration onset cueing is a term for the cueing principle used by a simulator motion platform.

In psychophysical perception, the Coriolis effect is the misperception of body orientation due to head movement while under the effect of rotation, often inducing nausea. This effect comes about as the head is moved in contrary or similar motion with the body during the time of a spin. This goes on to affect the vestibular system, particularly the semicircular canals which are affected by the acceleration. This causes a sense of dizziness or nausea before equilibrium is restored after the head returns to a stabilized state. Crucially, this illusion is based entirely upon perception, and is largely due to conflicting signals between one's sight and one's perception of their body position or motion. Examples of situations where this can arise are circular acceleration and movement during a circular rotation.

A sensation of falling occurs when the labyrinth or vestibular apparatus, a system of fluid-filled passages in the inner ear, detects changes in acceleration. This sensation can occur when a person begins to fall, which in terms of mechanics amounts to a sudden acceleration increase from zero to roughly 9.81 m/s2. If the body is in free fall with no other momenta, there is no falling sensation. This almost never occurs in real-life falling situations because when the faller leaves their support there are usually very significant quantities of residual momenta such as rotation and these momenta continue as the person falls, causing a sensation of dysphoria. The faller doesn't fall straight down but spins, flips, etc. due to these residual momenta and also due to the asymmetric forces of air resistance on their asymmetric body. While velocity continues to increase, the downward acceleration due to gravity remains constant. Increasing drag force may even cause a feeling of ascent.

The righting reflex, also known as the labyrinthine righting reflex, or the Cervico-collic reflex; is a reflex that corrects the orientation of the body when it is taken out of its normal upright position. It is initiated by the vestibular system, which detects that the body is not erect and causes the head to move back into position as the rest of the body follows. The perception of head movement involves the body sensing linear acceleration or the force of gravity through the otoliths, and angular acceleration through the semicircular canals. The reflex uses a combination of visual system inputs, vestibular inputs, and somatosensory inputs to make postural adjustments when the body becomes displaced from its normal vertical position. These inputs are used to create what is called an efference copy. This means that the brain makes comparisons in the cerebellum between expected posture and perceived posture, and corrects for the difference. The reflex takes 6 or 7 weeks to perfect, but can be affected by various types of balance disorders.

The leans is the most common type of spatial disorientation for aviators. Through stabilization of the fluid in the semicircular canals, a pilot may perceive straight and level flight while actually in a banked turn. This is caused by a quick return to level flight after a gradual, prolonged turn that the pilot failed to notice. The phenomenon consists of a false perception of angular displacement about the roll axis and therefore becomes an illusion of bank. This illusion is often associated with a vestibulospinal reflex that results in the pilot actually leaning in the direction of the falsely perceived vertical. Other common explanations of the leans are due to deficiencies of both otolith-organ and semicircular-duct sensory mechanisms.

Space neuroscience or astroneuroscience is the scientific study of the central nervous system (CNS) functions during spaceflight. Living systems can integrate the inputs from the senses to navigate in their environment and to coordinate posture, locomotion, and eye movements. Gravity has a fundamental role in controlling these functions. In weightlessness during spaceflight, integrating the sensory inputs and coordinating motor responses is harder to do because gravity is no longer sensed during free-fall. For example, the otolith organs of the vestibular system no longer signal head tilt relative to gravity when standing. However, they can still sense head translation during body motion. Ambiguities and changes in how the gravitational input is processed can lead to potential errors in perception, which affects spatial orientation and mental representation. Dysfunctions of the vestibular system are common during and immediately after spaceflight, such as space motion sickness in orbit and balance disorders after return to Earth.

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