Illusions of self-motion
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Illusions of self-motion (or "vection") occur when one perceives bodily motion despite no movement taking place. One can experience illusory movements of the whole body or of individual body parts, such as arms or legs.


Vestibular illusions

The
vestibular system 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 ...
is one of the major sources of information about one's own motion. Disorders of the visual system can lead to
dizziness Dizziness is an imprecise term that can refer to a sense of disorientation in space, vertigo, or lightheadedness. It can also refer to disequilibrium or a non-specific feeling, such as giddiness or foolishness. Dizziness is a common medical c ...
,
vertigo Vertigo is a condition where a person has the sensation of movement or of surrounding objects moving when they are not. Often it feels like a spinning or swaying movement. This may be associated with nausea, vomiting, sweating, or difficulties w ...
, and feelings of instability. Vertigo is not associated with illusory self-motion as it does not typically make you feel as though you are moving; however, in a subclass of vertigo known as subjective vertigo one does experience their own motion. People experience themselves being pulled heavily in one direction. There are also specific self-motion illusions that can occur through abnormal stimulation of various parts of the vestibular system, often encountered in aviation. This includes an illusion of inversion, in which one feels like they're tumbling backwards. Through various stimuli, people can be made to feel as if they are moving when they are not, not moving when they are, tilted when they are not, or not tilted when they are.


Visual illusions

When a large part of the visual field moves, viewers feel like they have moved and that the world is stationary. For example, when one is in a train at a station, and a nearby train moves, one can have the illusion that one's own train has moved in the opposite direction. Common sorts of vection include ''circular vection'', where an observer is placed at the center of rotation of a large vertically-oriented rotating drum, usually painted with vertical stripes; ''linear vection'', where an observer views a field that either approaches or recedes; and ''roll vection'', where an observer views a patterned disk rotating around their line of sight. During circular vection, the observer feels like they are rotating and the drum is stationary. During linear vection, the observer feels like they have moved forwards or backwards and the stimulus has stayed stationary. During roll vection, the observer feels like they have rotated around the line of sight and the disk has stayed stationary. Inducing vection can also induce
motion sickness 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 d ...
in susceptible individuals.


Auditory illusions

Compared to visually-induced vection, auditorily-induced vection is generally weaker. Auditory-induced vection can only be elicited in about 25% to 75% of the participants under laboratory conditions, and only when participants are
blindfold A blindfold (from Middle English ') is a garment, usually of cloth, tied to one's head to cover the human eye, eyes to disable the wearer's visual perception, sight. While a properly fitted blindfold prevents sight even if the eyes are open, a ...
ed. Most of the research has focused on eliciting circular vection horizontally about the body. Researchers have induced circular vection by mechanically rotating a buzzer around a subject in the dark or by presenting sound sequentially in one of several speakers arranged in a circular array. Adding auditory stimuli can significantly enhance visual, vestibular, and biomechanical vections.


Biomechanical illusions


Sea legs, dock rock, or stillness illness

After being on a small boat for a few hours and then going back onto land, it may feel like there is still rising and falling, as if one is still on the boat. It can also occur on other situations, such as after a long train journey or after working up a swaying tree. It is not clear whether sea legs are a form of
aftereffect Neural adaptation or sensory adaptation is a gradual decrease over time in the responsiveness of the sensory system to a constant Stimulus (physiology), stimulus. It is usually perception, experienced as a change in the stimulus. For example, if a ...
to the predominant frequency of the stimulation (e.g., the waves or the rocking of the train), whether it is a form of learning to adjust one's
gait Gait is the pattern of movement of the limbs of animals, including humans, during locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on speed, terrain, the need to maneuver, and energetic efficiency. Di ...
and
posture Posture or posturing may refer to: Medicine * Human position ** Abnormal posturing, in neurotrauma ** Spinal posture ** List of human positions * Posturography Posturography is the technique used to quantify postural control in upright stance in ...
. The "sea legs" condition needs to be distinguished from
mal de debarquement ''Mal de debarquement'' (or ''mal de débarquement'') syndrome (MdDS, or common name disembarkment syndrome) is a neurological condition usually occurring after a cruise, aircraft flight, or other sustained motion event. The phrase "mal de déba ...
, which is much more disturbing and long-lasting.


Circular treadmills

Linear treadmills by themselves generally do not induce illusions of self-motion. However, subjects report a strong sense of self-rotation from stepping along a circular treadmill in the dark, which can be further enhanced through auditory cues.


See also

*
Balance disorder A balance disorder is a disturbance that causes an individual to feel unsteady, for example when standing or walking. It may be accompanied by feelings of giddiness, or wooziness, or having a sensation of movement, spinning, or floating. Balance ...
*
Broken escalator phenomenon The broken escalator phenomenon, also known as the escalator effect and the Walker effect, is the sensation of losing balance, confusion or dizziness reported by some people when stepping onto an escalator which is not working. It is said that ther ...
*
Chronic subjective dizziness The term chronic subjective dizziness (CSD) is used to describe a commonly encountered type of dizziness that is not easily categorized into one of several other types, and for which the physical examination is typically normal. Patients with CSD ...
*
Ideomotor phenomenon The ideomotor phenomenon is a psychological phenomenon wherein a subject makes motions unconsciously. Also called ideomotor response (or ideomotor reflex) and abbreviated to IMR, it is a concept in hypnosis and psychological research. It is deri ...
*
Proprioception Proprioception ( ), also referred to as kinaesthesia (or kinesthesia), is the sense of self-movement, force, and body position. It is sometimes described as the "sixth sense". Proprioception is mediated by proprioceptors, mechanosensory neurons ...
*
Seasickness 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 d ...
*
Sense of balance 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 syste ...
, also known as equilibrioception *
Sensory illusions in aviation Human senses are not naturally geared for the inflight 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 o ...
*
Spatial disorientation Spatial disorientation results in a person being unable to determine their position or relative motion, commonly occurring during periods of challenging visibility, since vision is the dominant sense for orientation. The auditory system, vestibular ...
*
Tetris effect The ''Tetris'' effect (also known as ''Tetris'' syndrome) occurs when people devote so much time and attention to an activity that it begins to pattern their thoughts, mental images, and dreams. It takes its name from the video game ''Tetris''. ...


References

{{reflist Self-motion Motor control