Tau effect

Last updated

The tau effect is a spatial perceptual illusion that arises when observers judge the distance between consecutive stimuli in a stimulus sequence. When the distance from one stimulus to the next is constant, and the time elapsed from one stimulus to the next is also constant, subjects tend to judge the distances, correctly, as equal. However, if the distance from one stimulus to the next is constant, but the time elapsed from one stimulus to the next is not constant, then subjects tend to misperceive the interval that has the shorter temporal interval as also having a shorter spatial interval. [1] Thus, the tau effect reveals that stimulus timing affects the perception of stimulus spacing. Time is also a perceived quantity and subject to its own illusions; research indicates that in the tau effect, perceived stimulus spacing follows perceived (phenomenal) time rather than actual (physical) time. [2]

Contents

In different sensory modalities

The tau effect can occur with visual, [3] [4] auditory, [5] or tactile stimuli. [1] In touch, the tau effect was first described by Gelb (1914). [6] It was later given its name by Helson (1930) [7] and characterized in detail by Helson and King (1931). [1] In addition to the unimodal (i.e., purely visual, auditory, or tactile) tau effect, crossmodal tau effects can occur. For instance, Kawabe et al. (2008) [8] showed that the time intervals between auditory tones could affect subjects' perceptual judgements of the spatial interval between visual flashes in a manner consistent with that predicted by the tau effect.

Theories based in velocity expectation

Physically, traversed space and elapsed time are linked by velocity. It is logical, then, to consider that the tau effect occurs as a consequence of the brain's assumption regarding stimulus velocity. Indeed, different theories regarding the brain's expectations about stimulus velocity have been put forward in an effort to explain the tau effect.

Constant velocity hypothesis

According to the constant velocity hypothesis proposed by Jones and Huang (1982), [9] perception incorporates a prior expectation for constant speed. Therefore, given the temporal intervals marked by sequential stimuli, the brain expects spatial intervals that would yield constant velocity movement (i.e., uniform motion). [9] One limitation of this theory, pointed out by Goldreich (2007), [10] is that it does not explain why even two stimuli pressed in rapid succession against the skin are perceived as closer together the shorter the temporal interval between them is. In the absence of a third stimulus that creates a second spatial and temporal interval, the constant velocity hypothesis can have no bearing on this two-stimulus situation.

Low-speed expectation

According to a tactile Bayesian perceptual model [10] put forward by Goldreich (2007), the brain expects that tactile stimuli tend to move slowly. The Bayesian model reaches an optimal probabilistic inference by combining uncertain spatial and temporal sensory information with a prior expectation for low-speeds. The expectation that stimuli tend to move slowly results in the perceptual underestimation of the spatial separation between rapidly consecutive stimuli ("perceptual length contraction"), thereby reproducing the tau effect and related illusions.

Unlike the constant velocity hypothesis, the Bayesian model replicates the underestimation in perceived distance that occurs even when only two stimuli are presented in rapid succession. For the case of two taps to the skin, the Bayesian model [11] perceives the length between taps, l*, to be a function of the actual length, l, and the elapsed time, t:

l* = l/1 + 2(τ/t)2

The parameter tau (τ) is proportional to the observer's spatial uncertainty (specifically, it is the spatial standard deviation divided by the low-speed prior standard deviation). Consistent with this model, Tong et al. (2016) showed that stimulus pairs consisting of weaker taps, which are localized with greater uncertainty than stronger taps, result in more pronounced length contraction. [12] Modeling the tau effect that occurs in the perception of 3-tap sequences, Goldreich and Tong (2013) [11] compared the Bayesian model with a low-speed expectation to a Bayesian model with a low-acceleration expectation — similar to the constant-velocity hypothesis. They found that the low-speed prior model provided better fits to the human tactile tau effect data. When time is inaccurately perceived (i.e., because of the kappa effect), the Bayesian observer model judges stimulus spacing to follow perceived time rather than actual time, [10] consistent with reports from human subjects. [2]

A spatial perceptual illusion that seems to be closely related to the tau effect is the rabbit illusion. In the tactile rabbit illusion, [13] [14] a rapid sequence of taps delivered first near the wrist and then near the elbow creates the sensation of sequential taps hopping up the arm from the wrist towards the elbow, although no physical stimulus was applied between the two actual stimulus locations. Like the tau effect, the rabbit illusion has been observed not just in touch, but also in audition [15] and vision. [16]

If observers interpret rapid stimulus sequences in light of an expectation regarding velocity, then it would be expected that not only spatial, but also temporal illusions would result. This indeed occurs in the kappa effect: When the temporal separation between stimuli is constant and the spatial separation is varied, the observer's temporal interval judgment is influenced by the spatial distance between consecutive stimuli. Specifically, longer spatial intervals are perceived to occupy longer temporal intervals. The kappa effect is therefore the temporal perceptual analog of the tau effect.

Goldreich (2007) [10] linked the tau, rabbit, and kappa effects to the same underlying expectation regarding movement speed. He noted that, when stimuli move rapidly across space, "perception strikingly shrinks the intervening distance, and expands the elapsed time, between consecutive events". [10] Goldreich (2007) [10] termed these two fundamental perceptual distortions "perceptual length contraction" (tau effect, rabbit illusion) and "perceptual time dilation" (kappa effect) in analogy with the physical length contraction and time dilation of the theory of relativity. Perceptual length contraction and perceptual time dilation result from the same Bayesian observer model, one that expects stimuli to move slowly. [10] Analogously, in the theory of relativity, length contraction and time dilation both occur when a physical speed (the speed of light) cannot be exceeded.

General tau theory

Related Research Articles

Illusion Distortion of the perception of reality

An illusion is a distortion of the senses, which can reveal how the human brain normally organizes and interprets sensory stimulation. Though illusions distort our perception of reality, they are generally shared by most people.

A tactile illusion is an illusion that affects the sense of touch. Some tactile illusions require active touch, whereas others can be evoked passively. In recent years, a growing interest among perceptual researchers has led to the discovery of new tactile illusions and to the celebration of tactile illusions in the popular science press. Some tactile illusions are analogous to visual and auditory illusions, suggesting that these sensory systems may process information in similar ways; other tactile illusions don't have obvious visual or auditory analogs.

Phi phenomenon Optical illusion of perceiving continuous motion between separate objects viewed rapidly in succession

The term phi phenomenon is used in a narrow sense for an apparent motion that is observed if two nearby optical stimuli are presented in alternation with a relatively high frequency. In contrast to beta movement, seen at lower frequencies, the stimuli themselves do not appear to move. Instead, a diffuse, amorphous shadowlike something seems to jump in front of the stimuli and occlude them temporarily. This shadow seems to have nearly the color of the background. Max Wertheimer first described this form of apparent movement in his habilitation thesis, published 1912, marking the birth of Gestalt psychology.

Psychophysics quantitatively investigates the relationship between physical stimuli and the sensations and perceptions they produce. Psychophysics has been described as "the scientific study of the relation between stimulus and sensation" or, more completely, as "the analysis of perceptual processes by studying the effect on a subject's experience or behaviour of systematically varying the properties of a stimulus along one or more physical dimensions".

Postdiction involves explanation after the fact. In skepticism, it is considered an effect of hindsight bias that explains claimed predictions of significant events such as plane crashes and natural disasters. In religious contexts, theologians frequently refer to postdiction using the Latin term vaticinium ex eventu. Through this term, skeptics postulate that many biblical prophecies appearing to have come true may have been written after the events supposedly predicted, or that the text or interpretation may have been modified after the event to fit the facts as they occurred.

Motion perception process of inferring the speed and direction of elements in a scene based on visual, vestibular and proprioceptive inputs

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.

Retrodiction is the act of making a "prediction" about the past.

Multisensory integration, also known as multimodal integration, is the study of how information from the different sensory modalities may be integrated by the nervous system. A coherent representation of objects combining modalities enables animals to have meaningful perceptual experiences. Indeed, multisensory integration is central to adaptive behavior because it allows animals to perceive a world of coherent perceptual entities. Multisensory integration also deals with how different sensory modalities interact with one another and alter each other's processing.

The interstimulus interval is the temporal interval between the offset of one stimulus to the onset of another. For instance, Max Wertheimer did experiments with two stationary, flashing lights that at some interstimulus intervals appeared to the subject as moving instead of stationary. In these experiments, the interstimulus interval is simply the time between the two flashes. The ISI plays a large role in the phi phenomenon (Wertheimer) since the illusion of motion is directly due to the length of the interval between stimuli. When the ISI is shorter, for example between two flashing lines alternating back and forth, we perceive the change in stimuli to be movement. Wertheimer discovered that the space between the two lines is filled in by our brains and that the faster the lines alternate, the more likely we are to perceive it as one line moving back and forth. When the stimuli move fast enough, this creates the illusion of a moving picture like a movie or cartoon. Phi phenomenon is very similar to beta movement.

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.

Flash lag illusion Optical illusion

The flash lag illusion or flash-lag effect is a visual illusion wherein a flash and a moving object that appear in the same location are perceived to be displaced from one another). Several explanations for this simple illusion have been explored in the neuroscience literature.

Time perception is a field of study within psychology, cognitive linguistics and neuroscience that refers to the subjective experience, or sense, of time, which is measured by someone's own perception of the duration of the indefinite and unfolding of events. The perceived time interval between two successive events is referred to as perceived duration. Though directly experiencing or understanding another person's perception of time is not possible, such a perception can be objectively studied and inferred through a number of scientific experiments. Some temporal illusions help to expose the underlying neural mechanisms of time perception.

The cutaneous rabbit illusion is a tactile illusion evoked by tapping two or more separate regions of the skin in rapid succession. The illusion is most readily evoked on regions of the body surface that have relatively poor spatial acuity, such as the forearm. A rapid sequence of taps delivered first near the wrist and then near the elbow creates the sensation of sequential taps hopping up the arm from the wrist towards the elbow, although no physical stimulus was applied between the two actual stimulus locations. Similarly, stimuli delivered first near the elbow then near the wrist evoke the illusory perception of taps hopping from elbow towards wrist. The illusion was discovered by Frank Geldard and Carl Sherrick of Princeton University, in the early 1970s, and further characterized by Geldard (1982) and in many subsequent studies. Geldard and Sherrick likened the perception to that of a rabbit hopping along the skin, giving the phenomenon its name. While the rabbit illusion has been most extensively studied in the tactile domain, analogous sensory saltation illusions have been observed in audition and vision. The word "saltation" refers to the leaping or jumping nature of the percept.

Two-point discrimination

Two-point discrimination (2PD) is the ability to discern that two nearby objects touching the skin are truly two distinct points, not one. It is often tested with two sharp points during a neurological examination and is assumed to reflect how finely innervated an area of skin is. In clinical settings, two-point discrimination is a widely used technique for assessing tactile perception. It relies on the ability and/or willingness of the patient to subjectively report what they are feeling and should be completed with the patient’s eyes closed. The therapist may use calipers or simply a reshaped paperclip to do the testing. The therapist may alternate randomly between touching the patient with one point or with two points on the area being tested. The patient is asked to report whether one or two points was felt. The smallest distance between two points that still results in the perception of two distinct stimuli is recorded as the patient's two-point threshold. Performance on the two extremities can be compared for discrepancies. Although the test is still commonly used clinically, it has been roundly criticized by many researchers as providing an invalid measure of tactile spatial acuity, and several highly regarded alternative tests have been proposed to replace it.

Bayesian approaches to brain function investigate the capacity of the nervous system to operate in situations of uncertainty in a fashion that is close to the optimal prescribed by Bayesian statistics. This term is used in behavioural sciences and neuroscience and studies associated with this term often strive to explain the brain's cognitive abilities based on statistical principles. It is frequently assumed that the nervous system maintains internal probabilistic models that are updated by neural processing of sensory information using methods approximating those of Bayesian probability.

Perceptual learning is learning better perception skills such as differentiating two musical tones from one another or categorizations of spatial and temporal patterns relevant to real-world expertise. Examples of this may include reading, seeing relations among chess pieces, and knowing whether or not an X-ray image shows a tumor.

Chronostasis is a type of temporal illusion in which the first impression following the introduction of a new event or task-demand to the brain can appear to be extended in time. For example, chronostasis temporarily occurs when fixating on a target stimulus, immediately following a saccade. This elicits an overestimation in the temporal duration for which that target stimulus was perceived. This effect can extend apparent durations by up to 500 ms and is consistent with the idea that the visual system models events prior to perception.

Visual tilt effects

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.

Biological motion perception is the act of perceiving the fluid unique motion of a biological agent. The phenomenon was first documented by Swedish perceptual psychologist, Gunnar Johansson, in 1973. There are many brain areas involved in this process, some similar to those used to perceive faces. While humans complete this process with ease, from a computational neuroscience perspective there is still much to be learned as to how this complex perceptual problem is solved. One tool which many research studies in this area use is a display stimuli called a point light walker. Point light walkers are coordinated moving dots that simulate biological motion in which each dot represents specific joints of a human performing an action.

Fröhlich effect

The Fröhlich effect is a visual illusion wherein the first position of a moving object entering a window is misperceived. When observers are asked to localize the onset position of the moving target, they typically make localization errors in the direction of movement.

References

  1. 1 2 3 Helson, H.; King, S. M. (1931). "The tau effect: an example of psychological relativity". Journal of Experimental Psychology. 14 (3): 202–217. doi:10.1037/h0071164.
  2. 1 2 Russo, G.; Dellantonio, A. (June 1989). "Influence of phenomenal time on perceived space". Perceptual and Motor Skills. 68 (3 Pt 1): 971–84. doi:10.2466/pms.1989.68.3.971. PMID   2748315.
  3. ↑ Christopher Bill, J.; Teft, Leon W. (November 1972). "Space-time relations: the effects of variations in stimulus and interstimulus interval duration on perceived visual extent". Acta Psychologica. 36 (5): 358–69. doi:10.1016/0001-6918(72)90032-7. PMID   4644729.
  4. ↑ Sarrazin, Jean-Christophe; Giraudo, Marie-Dominique; Pailhous, Jean; Bootsma, Reinoud J.; Giraudo, MD (June 2004). "Dynamics of balancing space and time in memory: tau and kappa effects revisited". Journal of Experimental Psychology: Human Perception and Performance. 30 (3): 411–30. CiteSeerX   10.1.1.533.1030 . doi:10.1037/0096-1523.30.3.411. PMID   15161376.
  5. ↑ Sarrazin, Jean-Christophe; Giraudo, Marie-Dominique; Pittenger, John Bruce (March 2007). "Tau and Kappa effects in physical space: the case of audition". Psychological Research. 71 (2): 201–18. doi:10.1007/s00426-005-0019-1. PMID   16211410.
  6. ↑ Gelb, A. (April 1914). "Versuche auf dem Gebiete der Zeit- und Raumanschauung". In Schumann, F. (ed.). Bericht über den VI. Kongress für experimentelle Psychologie: in Göttingen. pp. 36–42.
  7. ↑ Helson, H. (May 23, 1930). "The tau effect -- an example of psychological relativity". Science. 71 (1847): 536–7. Bibcode:1930Sci....71..536H. doi:10.1126/science.71.1847.536. PMID   17799065.
  8. ↑ Kawabe, Takahiro; Miura, Kayo; Yamada, Yuki (June 2008). "Audiovisual tau effect". Acta Psychologica. 128 (2): 249–54. doi:10.1016/j.actpsy.2008.01.004. hdl: 2324/12407 . PMID   18328993.
  9. 1 2 Jones, Bill; Huang, Yih Lehr (1982). "Space-time dependencies in psychophysical judgment of extent and duration: algebraic models of the tau and kappa effects". Psychological Bulletin. 91 (1): 128–142. doi:10.1037/0033-2909.91.1.128.
  10. 1 2 3 4 5 6 7 Goldreich, D (Mar 28, 2007). "A Bayesian perceptual model replicates the cutaneous rabbit and other tactile spatiotemporal illusions". PLoS ONE. 2 (3): e333. Bibcode:2007PLoSO...2..333G. doi:10.1371/journal.pone.0000333. PMC   1828626 . PMID   17389923.
  11. 1 2 Goldreich, Daniel; Tong, Jonathan (10 May 2013). "Prediction, Postdiction, and Perceptual Length Contraction: A Bayesian Low-Speed Prior Captures the Cutaneous Rabbit and Related Illusions". Frontiers in Psychology. 4: 221. doi:10.3389/fpsyg.2013.00221. PMC   3650428 . PMID   23675360.
  12. ↑ Tong, Jonathan; Ngo, Vy; Goldreich, Daniel (1 August 2016). "Tactile length contraction as Bayesian inference". Journal of Neurophysiology. 116 (2): 369–379. doi:10.1152/jn.00029.2016. PMC   4969385 . PMID   27121574.
  13. ↑ Geldard, F. A.; Sherrick, C. E. (13 October 1972). "The Cutaneous "Rabbit": A Perceptual Illusion". Science. 178 (4057): 178–179. Bibcode:1972Sci...178..178G. doi:10.1126/science.178.4057.178. PMID   5076909.
  14. ↑ Geldard, Frank A. (July 1982). "Saltation in somesthesis". Psychological Bulletin. 92 (1): 136–75. doi:10.1037/0033-2909.92.1.136. PMID   7134325.
  15. ↑ Bremer, CD; Pittenger, JB; Warren, R; Jenkins, JJ (December 1977). "An illusion of auditory saltation similar to the cutaneous "rabbit"". The American Journal of Psychology. 90 (4): 645–54. doi:10.2307/1421738. JSTOR   1421738. PMID   610449.
  16. ↑ Geldard, FA (June 1976). "The saltatory effect in vision". Sensory Processes. 1 (1): 77–86. PMID   1029079.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.