autokinetic effect

   Also referred to as autokinetic sensation, autokinetic illusion, autokinetic phenomenon, autokinesis, and Charpentier's illusion. The term autokinetic effect is indebted to the Greek words automatos (automatically, driven by a power of its own) and kinèsis (movement). It translates loosely as self-movement effect. The adjective autokinetic was introduced in or shortly before 1887 by the German physiologist Hermann Rudolph Aubert (1826-1892). The eponym Charpentier's illusion refers to the French ophthalmologist and physiologist Augustin Charpentier (1852-1916). Although the term Charp-entier's illusion is used mainly as an equivalent of the term * size-weight illusion, in the literature it can also be found as applying to the autokinetic effect. The autokinetic effect consists of the illusory motion of a small object or stimulus against a contrasting, uniform background (i.e. a light spot against a uniformly dark background or a dark spot against a uniformly light background). The illusory motion typically commences after a few seconds of visual fixation. As a phenomenon, the autokinetic effect was probably recorded for the first time in 1799 by the German naturalist and explorer Friedrich Heinrich Alexander Freiherr von Humboldt (17691859). Von Humboldt discovered it while observing the stars from a mountain peak in Tener-ife and called it Sternschwanken ('star swinging'). In the German literature the illusory motion of a black spot against a light background is traditionally called Punktschwanken ('dot swinging'). The angular velocity of the illusory movement in question tends to be 2° to 3° per second, and the total movement may cover 30° or more, especially in cases of marked ocular or general fatigue and a constrained eye position. The neurophysiological correlates of the autoki-netic effect are not fully understood. Initially Sternschwanken wasbelievedtoresultfromthe actual, physical movement of the stars and/or the light emanating from them. It was not until the mid-19th century that an author named G. Schweizer had a star observed by different persons simultaneously, and thus discovered that the movement is actually illusory in nature. Ever since, the autokinetic effect has been classified as a * physiological illusion. It has traditionally been assumed that slow, involuntary movements of the eyeball may play a part in its mediation or that it may constitute an * aftereffect of postural shift or body movement. The possibility of a central mediation of the autokinetic effect has also been suggested. The latter thesis has been the object of renewed interest in relation to neuroimaging research suggesting the involvement of bilateral activity in the motion-sensitive middle occipito-temporal area known as MT/V5. As the autokinetic effect tends to respond to suggestion, it has of old also been labelled a psychogenic phenomenon (i.e. a *cognitive illusion). Autokinetic effects have been described in the visual modality (i.e. visual autokinetic effects) and in the auditory modality (i.e. auditory autokinetic effects). The auditory autoki-netic effect consists of an illusory spatial displacement of sounds, often combined with variations in loudness and pitch. The phenomenon was probably described for the first time in 1957 by the American cognitive psychologists Alfred C. Bernardin and Howard Ernest Gruber (19222005). The autokinetic effect should not be confused with * oscillopsia.

   References

   Charpentier, A. (1886). Sur une illusion visuelle. Comptes Rendus de l'Académie des Sciences, 102, 1155-1157.

   Adams, H.F. (1912). Autokinetic sensations. Psychological Monographs, 14, 1-45.

   Bernardin, A.C., Gruber, H.E. (1957). An auditory autokinetic effect. American Journal of Psychology, 70, 133-134.

   Gregory, R.L., Zangwill, O.L. (1963). The origin of the autokinetic effect. Quarterly Journal of Experimental Psychology, 15, 252-261.

   Anderson, D.C., Moss, C.A. (1964). The auditory autokinetic effect. American Journal of Psychology, 77, 502-503.

   Riedel, E., Stephan, Th., Deutschländer, A., Kalla, R., Wiesmann, M., Dieterich, M., Brandt, Th. (2005). Imaging the visual autoki-netic illusion with fMRI. Neuroimage, 27, 163-166.