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= Visual perceptual asynchrony (GENERALIZING AND RE-DRAFTING THE PERCEPTUAL ASYNCHRONY PAGE) =

In a variety of circumstances, visual features that are presented simultaneously are not perceived as simultaneous. Instead, they are perceived asynchronously, and this is typically explained by differences in how long different visual signals require to be processed by the eye and brain.

For example, the retinal signals evoked when looking at an object defined by large differences in light (high contrast) reach the brain faster than do the signals from objects defined by small differences in the amount of light. Here are some perceptual phenomena that have been explained in this way:


 * The Pulfrich effect involves viewing a moving object with both eyes but using a filter to reduce the luminance of the image going to one of the eyes. This causes the object to be perceived as moving in depth, in a fashion that is predicted by the proposal that signals with lower luminance take longer to propagate from the retina through to the visual cortex. yields about a 15 ms delay for a factor of ten difference in average retinal illuminance.[8][9][10][11] PULFRICH EFFECT PAGE HAS A GOOD ORGANIZATION?
 * The Hess effect. For two laterally-moving objects that are spatially aligned but have very different luminance against a dark background, the lower-luminance object is perceived to lag the brighter object. The amount by which this occurs suggests a difference in neural latency for a given amount of luminance difference that is approximately consistent with what is suggested by the Pulfrich effect.
 * The peripheral drift illusion. one variant of which is the rotating snakes illusion, has also been explained by this Faubert, J. & Herbert, A.M. (1999). However, another theory is blah blah.
 * An unnamed phenomenon involves stimuli comprised of hundreds of dots that are perceived as forming a global pattern. A study modified these patterns by coloring half of the dots darker than the background and half of the dots brighter than the background, while maintaining equivalent luminance contrast. This display yielded motion percepts that were not expected based on traditional models of motion perception. The motion percepts can be explained, however, if one adds to the models that dots darker than the background require a few more milliseconds to reach the brain's motion detectors than the dots that are brighter than the background. . Neural recordings with other stimuli are consistent with this explanation – neurons in the retina that signal increments in luminance respond several milliseconds faster than those that signal decrements in luminance.

Asynchronies related to eye movements
Saccadic remapping

Color-motion asynchrony
Certain displays yield evidence that in perception, color signals require up to 100 ms longer to process than do motion signals.

The experiments through which perceptual asynchrony was derived were pairing experiments in which subjects are asked to determine the color and direction of a single stimulus that is moving up and down (or right and left) and changing its color from, say red to green, while doing so – the change in the color and direction of motion being in and out of phase with respect to each other.

One of the most dramatic was first documented by Konstantinos Moutoussis and Semir Zeki in 1997. the term may most commonly be used by one

Perceptual asynchrony was first demonstrated by Konstantinos Moutoussis and Semir Zeki in 1997. In their work, Moutoussis and Zeki describe that people perceive the color and direction of motion of a visual stimulus with a time lag - they may perceive the color before the direction of motion. They quantified this time gap to be between 70 – 80 milliseconds.

There are several variants of this experiment, all leading to the same result. The asynchrony extends to the simultaneously presented color and orientation of lines, when it is found that the color is perceived before the orientation by about 40 milliseconds. The degree of perceptual asynchrony can be considerably reduced by manipulating the stimuli in a variety of ways,  which has led to the suggestion that the asynchrony is the result of differences in processing times taken to bring different attributes to a perceptual level.

The demonstration has far-reaching consequences because it shows


 * that two attributes, presented simultaneously in terms of physical reality, are not perceived simultaneously but asynchronously;
 * that, as a result, the brain incorrectly binds the two presented attributes, in other words that it binds an attribute perceived at one moment with the other attribute that had been perceived some 40 to 80 ms earlier;
 * that, consequently, there is no brain system or area that “waits” for all visual attributes to be brought up to a perceptual level before binding them together to give a percept in which the two attributes are seen in perfect registration.

The demonstration has consequences for understanding neural binding and consciousness and has led to the theory of Micro-Consciousness.

Theories
Perceptual asynchrony has been confirmed in many laboratories. It has also been shown it depends on the asynchronous perception of attributes rather than the perception of changes. If in a similar color - direction of motion pairing experiment, subjects are asked when a change in the two attributes occurred, without reporting the colour or direction of motion of the attribute, there is no perceptual asynchrony. Whether an asynchrony is observed or not depends, therefore, on the task.

Perceptual asynchrony has been accounted for by supposing that visual properties such as color, direction of motion and orientation of lines are processed at different speeds and therefore brought to perceptual completion at different times. Other interpretations to account for this perceptual asynchrony have been given. One such interpretation posits that there is a brain ‘time marker’ while another posits that the asynchrony can be accounted for by positing that access to brain color “transients” is stronger than that to motion “transients”.

Related phenomena
In a variety of tasks, response times to dim or low-contrast stimuli are longer than response times to high-contrast stimuli. This is likely in part due to longer sensory latencies, as described above, but also longer processing times at more cognitive, decision stages of the brain.