The barberpole illusion is a visual illusion that reveals biases in the processing of visual motion in the human brain. This visual illusion occurs when a diagonally striped pole is rotated around its vertical axis (horizontally), it appears as though the stripes are moving in the direction of its vertical axis (downwards in the case of the animation to the right) [1] rather than around it. [2]
The barber's pole is commonly found outside barber shops.
In 1929, psychologist J.P. Guilford informally noted a paradox in the perceived motion of stripes on a rotating barber pole. The barber pole turns in place on its vertical axis, but the stripes appear to move upwards rather than turning with the pole. [3] Guilford tentatively attributed the phenomenon to eye movements, but acknowledged the absence of data on the question.
In 1935, Hans Wallach published a comprehensive series of experiments related to this topic, [4] but since the article was in German it was not immediately known to English-speaking researchers. An English summary of the research was published in 1976 [5] and a complete English translation of the 1935 paper was published in 1996. [6] Wallach's analysis focused on the interaction between the terminal points of the diagonal lines and the implicit aperture created by the edges of the pole.
This illusion occurs because a bar or contour within a frame of reference provides ambiguous information about its "real" direction of movement. The actual motion of the line has many possibilities. The shape of the aperture thus tends to determine the perceived direction of motion for an otherwise identically moving contour. A vertically elongated aperture makes vertical motion dominant whereas a horizontally elongated aperture makes horizontal motion dominant. In the case of a circular or square aperture, the perceived direction of movement is usually orthogonal to the orientation of the stripes (diagonal, in this case). The perceived direction of movement relates to the termination of the line's end points within the inside border of the occluder. The vertical aperture, for instance, has longer edges at the vertical orientation, creating a larger number of terminators unambiguously moving vertically. This stronger motion signal forces us to perceive vertical motion. Functionally, this mechanism has evolved to ensure that we perceive a moving pattern as a rigid surface moving in one direction. [7]
Individual motion-sensitive neurons in the visual system have only limited information, as they see only a small portion of the visual field (a situation referred to as the "aperture problem"). In the absence of additional information the visual system prefers the slowest possible motion: i.e., motion orthogonal to the moving line. [8] The neurons which may correspond to perceiving barber-pole-like patterns have been identified in the visual cortex of ferrets. [9]
A similar effect occurs in the Shepard's tone, which is an auditory illusion. [1] [2]
A rotation is a circular movement of an object around a center of rotation. The geometric plane along which the rotation occurs is called the rotation plane, and the imaginary line extending from the center and perpendicular to the rotation plane is called the rotation axis. A three-dimensional object can always be rotated about an infinite number of rotation axes.
An illusion is a distortion of the senses, which can reveal how the human brain normally organizes and interprets sensory stimulation. Although illusions distort our perception of reality, they are generally shared by most people.
An optical illusion is an illusion caused by the visual system and characterized by a visual percept that arguably appears to differ from reality. Illusions come in a wide variety; their categorization is difficult because the underlying cause is often not clear but a classification proposed by Richard Gregory is useful as an orientation. According to that, there are three main classes: physical, physiological, and cognitive illusions, and in each class there are four kinds: Ambiguities, distortions, paradoxes, and fictions. A classical example for a physical distortion would be the apparent bending of a stick half immerged in water; an example for a physiological paradox is the motion aftereffect. An example for a physiological fiction is an afterimage. Three typical cognitive distortions are the Ponzo, Poggendorff, and Müller-Lyer illusion. Physical illusions are caused by the physical environment, e.g. by the optical properties of water. Physiological illusions arise in the eye or the visual pathway, e.g. from the effects of excessive stimulation of a specific receptor type. Cognitive visual illusions are the result of unconscious inferences and are perhaps those most widely known.
Depth perception is the visual ability to perceive the world in three dimensions (3D) and the distance of an object. Depth sensation is the corresponding term for animals, since although it is known that animals can sense the distance of an object, it is not known whether they perceive it in the same subjective way that humans do.
Sound localization is a listener's ability to identify the location or origin of a detected sound in direction and distance.
The term illusory motion, also known as motion illusion, is an optical illusion in which a static image appears to be moving due to the cognitive effects of interacting color contrasts, object shapes, and position. Apparent motion is the most common type of illusory motion and is perceived when images are displayed in succession at a specific frame rate such as in a movie.
Motion perception is the process of inferring the speed and direction of elements in a scene based on visual, vestibular and proprioceptive inputs. Although this process appears straightforward to most observers, it has proven to be a difficult problem from a computational perspective, and difficult to explain in terms of neural processing.
A barber's pole is a type of sign used by barbers to signify the place or shop where they perform their craft. The trade sign is, by a tradition dating back to the Middle Ages, a staff or pole with a helix of colored stripes. The pole may be stationary or may rotate, often with the aid of an electric motor.
The kappa effect or perceptual time dilation is a temporal perceptual illusion that can arise when observers judge the elapsed time between sensory stimuli applied sequentially at different locations. In perceiving a sequence of consecutive stimuli, subjects tend to overestimate the elapsed time between two successive stimuli when the distance between the stimuli is sufficiently large, and to underestimate the elapsed time when the distance is sufficiently small.
Akinetopsia, also known as cerebral akinetopsia or motion blindness, is a rare neuropsychological disorder in which a patient cannot perceive motion in their visual field, despite being able to see stationary objects without issue. There are varying degrees of akinetopsia: from seeing motion as frames of a cinema reel to an inability to discriminate any motion. There is currently no effective treatment or cure for akinetopsia.
In visual perception, the kinetic depth effect refers to the phenomenon whereby the three-dimensional structural form of an object can be perceived when the object is moving. In the absence of other visual depth cues, this might be the only perception mechanism available to infer the object's shape. Being able to identify a structure from a motion stimulus through the human visual system was shown by Wallach and O'Connell in the 1950s through their experiments.
Parallax scanning depth enhancing imaging methods rely on discrete parallax differences between depth planes in a scene. The differences are caused by a parallax scan. When properly balanced (tuned) and displayed, the discrete parallax differences are perceived by the brain as depth.
The spinning dancer, also known as the silhouette illusion, is a kinetic, bistable, animated optical illusion originally distributed as a GIF animation showing a silhouette of a pirouetting female dancer. The illusion, created in 2003 by Japanese web designer Nobuyuki Kayahara, involves the apparent direction of motion of the figure. Some observers initially see the figure as spinning clockwise and some counterclockwise. Additionally, some may see the figure suddenly spin in the opposite direction.
Illusions of self-motion 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.
The vertical–horizontal illusion is the tendency for observers to overestimate the length of a vertical line relative to a horizontal line of the same length. This involves a bisecting component that causes the bisecting line to appear longer than the line that is bisected. People often overestimate or underestimate the length of the bisecting line relative to the bisected line of the same length. This even happens if people are aware that the lines are of the same length.
Oblique effect is the name given to the relative deficiency in perceptual performance for oblique contours as compared to the performance for horizontal or vertical contours.
Due to the effect of a spatial context or temporal context, the perceived orientation of a test line or grating pattern can appear tilted away from its physical orientation. The tilt illusion (TI) is the phenomenon that the perceived orientation of a test line or grating is altered by the presence of surrounding lines or grating with a different orientation. And the tilt aftereffect (TAE) is the phenomenon that the perceived orientation is changed after prolonged inspection of another oriented line or grating.
Hans Wallach was a German-American experimental psychologist whose research focused on perception and learning. Although he was trained in the Gestalt psychology tradition, much of his later work explored the adaptability of perceptual systems based on the perceiver's experience, whereas most Gestalt theorists emphasized inherent qualities of stimuli and downplayed the role of experience. Wallach's studies of achromatic surface color laid the groundwork for subsequent theories of lightness constancy, and his work on sound localization elucidated the perceptual processing that underlies stereophonic sound. He was a member of the National Academy of Sciences, a Guggenheim Fellow, and recipient of the Howard Crosby Warren Medal of the Society of Experimental Psychologists.
Interindividual differences in perception describes the effect that differences in brain structure or factors such as culture, upbringing and environment have on the perception of humans. Interindividual variability is usually regarded as a source of noise for research. However, in recent years, it has become an interesting source to study sensory mechanisms and understand human behavior. With the help of modern neuroimaging methods such as fMRI and EEG, individual differences in perception could be related to the underlying brain mechanisms. This has helped to explain differences in behavior and cognition across the population. Common methods include studying the perception of illusions, as they can effectively demonstrate how different aspects such as culture, genetics and the environment can influence human behavior.
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