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. [1] [2] Several explanations for this simple illusion have been explored in the neuroscience literature (for a review, see [3] ).
The first proposed explanation for the flash-lag effect is that the visual system is predictive, accounting for neural delays by extrapolating the trajectory of a moving stimulus into the future. [2] [4] In other words, when light from a moving object hits the retina, a certain amount of time is required before the object is perceived. In that time, the object has moved to a new location in the world. The motion extrapolation hypothesis asserts that the visual system will take care of such delays by extrapolating the position of moving objects forward in time.
A second proposed explanation is that the visual system processes moving objects more quickly than flashed objects. This latency-difference hypothesis asserts that by the time the flashed object is processed, the moving object has already moved to a new position. [5] [6] The latency-difference proposal tacitly rests on the assumption that awareness (what the subject reports) is an on-line phenomenon, coming about as soon as a stimulus reaches its "perceptual end-point". [7]
Eagleman & Sejnowski (2000abc) proposed a third alternative: [8] [9] [10] [11] [12] visual awareness is neither predictive nor on-line, but is instead postdictive, such that the percept attributed to the time of the flash is a function of events that happen in the ~80 ms following the flash. This postdictive framework is consistent with findings in other fields, such as backward masking in visual psychophysics (Bachmann, 1994), or the color phi phenomenon. [13] In backward masking, a stimulus followed in rapid succession by a second stimulus can block or modify the perception of the first one. In the color phi phenomenon, two colored dots presented sequentially within a small time and distance will appear to have changed color in the middle of their apparent trajectory. Since the viewer cannot know what the color of the second dot will be until having seen the second dot, the only explanation is that the conscious percept attributed to the "trajectory" of the dots is formed after the second dot has "arrived" at its destination. Eagleman & Sejnowski found that the perception attributed to the time of the flash depends on events in the next ~80 ms after the flash. [14] In this way, they drew a correspondence [15] between the flash-lag effect and the Fröhlich effect, [16] wherein the first position of a moving object entering a window is misperceived.
A recent study tries to reconcile these different approaches by approaching perception as an inference mechanism aiming at describing what is happening at the present time. [17] In particular, it could extend the motion extrapolation hypothesis by weighting this prediction by the precision of the current information. Thus, the corrected position of the moving target is calculated by combining the sensory flux with the internal representation of the trajectory, both of which exist in the form of probability distributions. To manipulate the trajectory is to change the precision and therefore the relative weight of these two information when they are optimally combined in order to know where an object is at the present time. For an object that moves predictably, the neural network can infer its most probable position taking into account this processing time. For the flash, however, this prediction can not be established because its appearance is unpredictable. Thus, while the two targets are aligned on the retina at the time of the flash, the position of the moving object is anticipated by the brain to compensate for the processing time: it is this differentiated treatment that causes the flash-lag effect. Moreover, this could also explain related phenomena such as motion reversal. [18]
An illusion is a distortion of the senses, which can reveal how the mind normally organizes and interprets sensory stimulation. Although illusions distort the human perception of reality, they are generally shared by most people.
In visual perception, 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.
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.
Blindsight is the ability of people who are cortically blind to respond to visual stimuli that they do not consciously see due to lesions in the primary visual cortex, also known as the striate cortex or Brodmann Area 17. The term was coined by Lawrence Weiskrantz and his colleagues in a paper published in a 1974 issue of Brain. A previous paper studying the discriminatory capacity of a cortically blind patient was published in Nature in 1973. The assumed existence of blindsight is controversial, with some arguing that it is merely degraded conscious vision.
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.
The Ternus illusion, also commonly referred to as the Ternus Effect, is an illusion related to human visual perception involving apparent motion. In a simplified explanation of one form of the illusion, two discs, are shown side by side as the first frame in a sequence of three frames. Next a blank frame is presented for a very short, variable duration. In the final frame, two similar discs are then shown in a shifted position. Depending on various factors including the time intervals between frames as well as spacing and layout, observers perceive either element motion, in which L appears to move to R while C remains stationary or they report experiencing group motion, in which L and C appear to move together to C and R. Both element motion and group motion can be observed in animated examples to the right in Figures 1 and 2.
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 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.
The wagon-wheel effect is an optical illusion in which a spoked wheel appears to rotate differently from its true rotation. The wheel can appear to rotate more slowly than the true rotation, it can appear stationary, or it can appear to rotate in the opposite direction from the true rotation.
The Hering illusion is one of the geometrical-optical illusions and was discovered by the German physiologist Ewald Hering in 1861. When two straight and parallel lines are presented in front of radial background, the lines appear as if they were bowed outwards. The Orbison illusion is one of its variants, while the Wundt illusion produces a similar, but inverted effect.
The lilac chaser is a visual illusion, also known as the Pac-Man illusion. It consists of 12 lilac, blurred discs arranged in a circle, around a small black, central cross on a grey background. One of the discs disappears briefly, then the next, and the next, and so on, in a clockwise direction. When one stares at the cross for at least 30 seconds, one sees three illusions
The study of time perception or chronoception is a field 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, 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.
In cognitive neuroscience, visual modularity is an organizational concept concerning how vision works. The way in which the primate visual system operates is currently under intense scientific scrutiny. One dominant thesis is that different properties of the visual world require different computational solutions which are implemented in anatomically/functionally distinct regions that operate independently – that is, in a modular fashion.
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.
Motion Induced Blindness (MIB), also known as Bonneh's illusion is a visual illusion in which a large, continuously moving pattern erases from perception some small, continuously presented, stationary dots when one looks steadily at the center of the display. It was discovered by Bonneh, Cooperman, and Sagi (2001), who used a swarm of blue dots moving on a virtual sphere as the larger pattern and three small yellow dots as the smaller pattern. They found that after about 10 seconds, one or more of the dots disappeared for brief, random times.
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 half a second and is consistent with the idea that the visual system models events prior to perception.
In visual perception, structure from motion (SFM) refers to how humans recover depth structure from object's motion. The human visual field has an important function: capturing the three-dimensional structures of an object using different kinds of visual cues.
Motion silencing is an illusion or perceptual phenomenon in which objects that are rapidly changing in a particular salient property seem to cease changing with motion. The illusion was first identified by Jordan Suchow and George Alvarez in the publication of their research on the topic.
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.
Visual crowding is the inability to view a target stimulus distinctly when presented in a clutter. Crowding impairs the ability to discriminate object features and contours among flankers, which in turn impairs people's ability to respond appropriately to the target stimulus.
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