Flash lag illusion

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.{{cite journal|last1=Khurana|first1=Beena|last2=Nijhawan|first2=Romi|title=Extrapolation or attention shift?|journal=Nature|date=7 December 1995|volume=378|issue=6557|pages=566|doi=10.1038/378566a0|bibcode=1995Natur.378..566K |s2cid=4307819 |doi-access=free}} 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.{{cite journal|last1=Whitney|first1=David|last2=Murakami|first2=Ikuya|journal=Nature Neuroscience|title=Latency difference, not spatial extrapolation|date=1 December 1998|volume=1|issue=8|pages=656–657|doi=10.1038/3659|pmid=10196580|s2cid=5784335 }}{{cite journal|last1=Purushothaman|first1=Gopathy|last2=Patel|first2=Saumil S.|last3=Bedell|first3=Harold E.|last4=Ogmen|first4=Haluk|title=Moving ahead through differential visual latency|journal=Nature|date=3 December 1998|volume=396|issue=6710|pages=424|doi=10.1038/24766|pmid=9853748|bibcode=1998Natur.396..424P |s2cid=4420101 |doi-access=free}} 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".{{cite journal|last1=Zeki|first1=S|last2=Bartels|first2=A|title=The asynchrony of consciousness.|journal=Proceedings: Biological Sciences|date=22 August 1998|volume=265|issue=1405|pages=1583–5|pmid=9744110|doi=10.1098/rspb.1998.0475|pmc=1689325}}

Eagleman & Sejnowski (2000abc) proposed a third alternative:{{cite journal|last1=Eagleman|first1=D. M.|title=Motion Integration and Postdiction in Visual Awareness|journal=Science|date=17 March 2000|volume=287|issue=5460|pages=2036–2038|doi=10.1126/science.287.5460.2036|pmid=10720334|bibcode=2000Sci...287.2036E |url=http://neuro.bcm.edu/eagleman/papers/EaglemanSejnowskiScience2000.pdf|access-date=18 June 2007|archive-url=https://web.archive.org/web/20070930015537/http://neuro.bcm.edu/eagleman/papers/EaglemanSejnowskiScience2000.pdf|archive-date=30 September 2007|url-status=dead}}{{cite journal|last1=Patel|first1=S. S.|title=Flash-Lag Effect: Differential Latency, Not Postdiction|journal=Science|date=10 November 2000|volume=290|issue=5494|pages=1051a–1051|doi=10.1126/science.290.5494.1051a|pmid=11184992|doi-access=free|citeseerx=10.1.1.299.7320}}{{cite journal|last1=Krekelberg|first1=Bart|last2=Lappe|first2=Markus|title=Temporal recruitment along the trajectory of moving objects and the perception of position|journal=Vision Research|date=August 1999|volume=39|issue=16|pages=2669–2679|doi=10.1016/S0042-6989(98)00287-9|pmid=10492829|doi-access=free}}{{cite journal|last1=Krekelberg|first1=B.|s2cid=2228258|title=The Position of Moving Objects|journal=Science|date=18 August 2000|volume=289|issue=5482|pages=1107a–1107|doi=10.1126/science.289.5482.1107a|pmid=17833394}}{{cite journal|last1=Eagleman|first1=D|title=Untangling spatial from temporal illusions|journal=Trends in Neurosciences|date=1 June 2002|volume=25|issue=6|pages=293|doi=10.1016/S0166-2236(02)02179-3|pmid=12086745|s2cid=8614307}} 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 {{nobr|~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.{{cite journal|last1=Kolers|first1=Paul A.|last2=von Grünau|first2=Michael|title=Shape and color in apparent motion|journal=Vision Research|date=January 1976|volume=16|issue=4|pages=329–335|doi=10.1016/0042-6989(76)90192-9|pmid=941407|s2cid=19376707 }} 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 {{nobr|~80 ms}} after the flash.{{cite journal|last1=Eagleman|first1=David M.|title=Visual illusions and neurobiology|journal=Nature Reviews Neuroscience|date=December 2001|volume=2|issue=12|pages=920–926|doi=10.1038/35104092|pmid=11733799|s2cid=205023280 |url=http://neuro.bcm.edu/eagleman/papers/Eagleman.NatureRevNeuro.Illusions.pdf|url-status=dead|archive-url=https://web.archive.org/web/20070927212714/http://neuro.bcm.edu/eagleman/papers/Eagleman.NatureRevNeuro.Illusions.pdf|archive-date=2007-09-27}} In this way, they drew a correspondence{{cite journal|last1=Eagleman|first1=D. M.|last2=Sejnowski|first2=T. J.|title=Motion signals bias localization judgments: A unified explanation for the flash-lag, flash-drag, flash-jump, and Frohlich illusions|journal=Journal of Vision|date=1 March 2007|volume=7|issue=4|pages=3|doi=10.1167/7.4.3|pmid=17461687|pmc=2276694}} between the flash-lag effect and the Fröhlich effect,{{cite journal|last1=Fröhlich|first1=Friedrich W.|title=Über die Messung der Empfindungszeit|journal=Pflügers Archiv für die gesamte Physiologie des Menschen und der Tiere|date=December 1924|volume=202|issue=1|pages=566–572|doi=10.1007/BF01723521|s2cid=1281712 }} 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.{{cite journal | vauthors = Khoei MA, Masson GS, Perrinet LU | title = The flash-lag effect as a motion-based predictive shift | journal = PLOS Computational Biology | volume = 13 | issue = 1 | pages = e1005068 | date = January 2017 | doi = 10.1371/journal.pcbi.1005068| pmid = 28125585 | pmc = 5268412 | bibcode = 2017PLSCB..13E5068K | doi-access = free }} 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.{{cite journal|last1=Rao|first1=Rajesh P. N.|last2=Eagleman|first2=David M.|last3=Sejnowski|first3=Terrence J.|title=Optimal Smoothing in Visual Motion Perception|journal=Neural Computation|date=June 2001|volume=13|issue=6|pages=1243–1253|doi=10.1162/08997660152002843|pmid=11387045|citeseerx=10.1.1.164.1678|s2cid=2277791 }}

• Tau effect
• Kappa effect
• Cutaneous rabbit illusion
• Temporal illusions
• Fröhlich effect

{{reflist}}

• {{cite journal | last1 = Baldo | first1 = M.V. | last2 = Klein | first2 = S.A. | year = 1995 | title = Extrapolation or attention shift?. | journal = Nature | volume = 378 | issue = 6557| pages = 565–6 | doi=10.1038/378565a0| pmid = 8524389 | bibcode = 1995Natur.378..565B | s2cid = 4306779 }}
• {{cite journal | last1 = Snowden | first1 = R.J. | last2 = Braddick | first2 = O.J. | year = 1989 | title = The combination of motion signals over time | journal = Vision Research | volume = 29 | issue = 11| pages = 1621–30 | doi=10.1016/0042-6989(89)90143-0| pmid = 2635485 | s2cid = 6015282 }}
• {{cite journal | last1 = Snowden | first1 = R.J. | last2 = Braddick | first2 = O.J. | year = 1991 | title = The temporal integration and resolution of velocity signals | journal = Vision Research | volume = 31 | issue = 5| pages = 907–14 | doi=10.1016/0042-6989(91)90156-y| pmid = 2035273 | s2cid = 16996397 }}

• [https://michaelbach.de/ot/mot-flashLag/index.html Interactive Demo] by Michael Bach

{{Optical illusions}}

Category:Optical illusions