Illusions of self-motion
||This article may be confusing or unclear to readers. (January 2009)|
Illusions of self-motion refers to a phenomenon that occurs when someone feels that their body is moving when no movement is taking place. One can experience illusory movements of the whole body or of individual body parts, such as arms or legs.
The vestibular system is one of the major sources of information about one's own motion. Disorders of the visual system can lead to dizziness, vertigo, and feelings of instability. Vertigo, a sensation that the world is spinning around oneself, is generally not an illusion of self motion because the sufferer of vertigo does not feel that their own body is moving. However, one experiences their own motion in a subclass of vertigo known as subjective vertigo. 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 that they're tumbling backwards.
When a large part of the visual field moves, a viewer feels 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 centre 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 his or her line of sight. During circular vection, the observer feels they are rotating and the drum is stationary, during linear vection, the observer feels they have moved forwards or backwards and the stimulus has stayed stationary, and during roll vection, the observer feels they have rotated around the line of sight and the disk has stayed stationary.
Inducing vection can also induce motion sickness in susceptible individuals.
Sea legs, dock rock, or stillness illness
After being on a small boat for a few hours and back onto land, one may feel that there is still rising and falling as if still on the boat. It can also occur on other situations, such as after a long train journey. It is not clear whether sea legs is a form of aftereffect 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 and posture, or whether it is a form of the Tetris effect. Sea legs needs to be distinguished from mal de debarquement, which is much more disturbing and long-lasting.
- Balance disorder
- Broken escalator phenomenon
- Ideomotor phenomenon
- Spatial disorientation