Editing Blindsight (section)

== Research ==
[[Lawrence Weiskrantz]] and colleagues showed in the early 1970s that if forced to guess about whether a stimulus is present in their blind field, some observers do better than chance.<ref>{{cite book|vauthors = Weiskrantz L|year=1986|title=Blindsight: A Case Study and Implications|publisher=[[Oxford University Press]]|isbn=978-0-19-852192-1|oclc=21677307|author-link=Lawrence Weiskrantz}}</ref>{{Page needed|date=January 2018}} This ability to detect stimuli that the observer is not conscious of can extend to discrimination of the type of stimulus (for example, whether an 'X' or 'O' has been presented in the blind field).{{cn|date=January 2024}}

[[Electrophysiological]] evidence from the late 1970s has shown that there is no direct retinal input from [[Cone cell|S-cones]] to the [[superior colliculus]], implying that the perception of [[color]] information should be impaired.<ref>{{cite journal|vauthors = de Monasterio FM|title = Properties of ganglion cells with atypical receptive-field organization in retina of macaques|journal = Journal of Neurophysiology|volume = 41|issue = 6|pages = 1435–49|date = November 1978|pmid = 104014|doi = 10.1152/jn.1978.41.6.1435}}</ref><ref>{{cite journal|vauthors = Marrocco RT, Li RH|title = Monkey superior colliculus: properties of single cells and their afferent inputs|journal = Journal of Neurophysiology|volume = 40|issue = 4|pages = 844–60|date = July 1977|pmid = 407333|doi = 10.1152/jn.1977.40.4.844}}</ref><ref>{{cite journal|vauthors = Schiller PH, Malpeli JG|title = Properties and tectal projections of monkey retinal ganglion cells|journal = Journal of Neurophysiology|volume = 40|issue = 2|pages = 428–45|date = March 1977|pmid = 403252|doi = 10.1152/jn.1977.40.2.428}}</ref> However, more recent evidence point to a pathway from S-cones to the superior colliculus, opposing previous research and supporting the idea that some chromatic processing mechanisms are intact in blindsight.<ref name=":1" /><ref>{{cite book|title=Brain & Behavior: An Introduction to Biological Psychology|vauthors = Garrett B|date=2011|publisher=SAGE Publications|isbn=978-1-4129-8168-2|edition=3rd|location=Thousand Oaks, California|pages=315–318|oclc=617425474}}</ref>

Patients shown images on their blind side of people expressing emotions correctly guessed the emotion most of the time. The movement of facial muscles used in smiling and frowning were measured and reacted in ways that matched the kind of emotion in the unseen image. Therefore, the emotions were recognized without involving conscious sight.<ref>{{cite journal|vauthors = Tamietto M, de Gelder B|title = Neural bases of the non-conscious perception of emotional signals|journal = Nature Reviews. Neuroscience|volume = 11|issue = 10|pages = 697–709|date = October 2010|pmid = 20811475|doi = 10.1038/nrn2889|s2cid = 4690318|hdl = 2318/79483|hdl-access = free}}</ref>

A study reported in 2008 asked patient GY to ''mis''state where in his visual field a distinctive stimulus was presented. If the stimulus was in the upper part of his visual field, he was to say it was in the lower part, and ''vice versa''. He was able to misstate, as requested, in his left visual field (with normal conscious vision); but he tended to fail in the task—to state the location correctly—when the stimulus was in his blindsight (right) visual field.<ref name="exclusion">{{cite journal|vauthors = Persaud N, Cowey A|title = Blindsight is unlike normal conscious vision: evidence from an exclusion task|journal = Consciousness and Cognition|volume = 17|issue = 3|pages = 1050–5|date = September 2008|pmid = 18065242|doi = 10.1016/j.concog.2007.10.002|s2cid = 30699219}}</ref> This failure rate worsened when the stimulus was clearer,<ref name="exclusion" /> indicating that failure was not simply due to unreliability of blindsight.

=== Evidence in animals ===
In a 1995 experiment, researchers attempted to show that monkeys with lesions in or even wholly removed striate cortexes also experienced blindsight. To study this, they had the monkeys complete tasks similar to those commonly used for human subjects. The monkeys were placed in front of a monitor and taught to indicate whether a stationary object or nothing was present in their visual field when a tone was played. Then the monkeys performed the same task except the stationary objects were presented outside of their visual field. The monkeys performed very similar to human participants and were unable to perceive the presence of stationary objects outside of their visual field.<ref>{{cite journal |vauthors=Cowey A, Stoerig P |date=January 1995 |title=Blindsight in monkeys |url=http://l3d.cs.colorado.edu/~ctg/classes/lib/cogsci/cowey.pdf |url-status=dead |journal=Nature |volume=373 |issue=6511 |pages=247–9 |bibcode=1995Natur.373..247C |doi=10.1038/373247a0 |pmid=7816139 |s2cid=4269412 |archive-url=https://web.archive.org/web/20120501114729/http://l3d.cs.colorado.edu/~ctg/classes/lib/cogsci/cowey.pdf |archive-date=2012-05-01 |access-date=2018-02-05}}</ref>

Another 1995 study by the same group sought to prove that monkeys could also be conscious of movement in their deficit visual field despite not being consciously aware of the presence of an object there. To do this, researchers used another standard test for humans which was similar to the previous study except moving objects were presented in the deficit visual field. Starting from the center of the deficit visual field, the object would either move up, down, or to the right. The monkeys performed identically to humans on the test, getting them right almost every time. This showed that the monkey's ability to detect movement is separate from their ability to consciously detect an object in their deficit visual field, and gave further evidence for the claim that damage to the striate cortex plays a large role in causing the disorder.<ref>{{cite journal |vauthors=Stoerig P, Cowey A |date=March 1997 |title=Blindsight in man and monkey |journal=Brain |volume=120 ( Pt 3) |issue=3 |pages=535–59 |doi=10.1093/brain/120.3.535 |pmid=9126063 |doi-access=free}}{{dead link|date=August 2020|bot=medic}}{{cbignore|bot=medic}}</ref>

Several years later, another study compared and contrasted the data collected from monkeys and that of a specific human patient with blindsight, GY. His striate cortical region was damaged through [[Physical trauma|trauma]] at the age of eight, though for the most part he retained full functionality, GY was not consciously aware of anything in his right visual field. In the monkeys, the striate cortex of the left hemisphere was surgically removed. By comparing the test results of both GY and the monkeys, the researchers concluded that similar patterns of responses to stimuli in the "blind" visual field can be found in both species.<ref>{{cite journal |vauthors=Cowey A, Alexander I, Stoerig P |date=February 2008 |title=A blindsight conundrum: how to respond when there isn't a correct response |journal=Neuropsychologia |volume=46 |issue=3 |pages=870–8 |doi=10.1016/j.neuropsychologia.2007.11.031 |pmid=18201733 |s2cid=20790934}}</ref>

===Case studies===
{{Tone|section|date=January 2018}}

==== "DB" ====
Researchers applied the same type of tests that were used to study blindsight in animals to a patient referred to as "DB". The normal techniques used to assess visual acuity in humans involved asking them to verbally describe some visually recognizable aspect of an object or objects. DB was given forced-choice tasks to complete instead. The results of DB's guesses showed that DB was able to determine shape and detect movement at some unconscious level, despite not being visually aware of this. DB himself chalked up the accuracy of his guesses to be merely coincidental.<ref name="Weiskrantz">{{cite journal|title=Blindsight|journal=Scholarpedia|volume=2|issue=4|pages=3047|vauthors = Weiskrantz L|doi=10.4249/scholarpedia.3047|year=2007|bibcode=2007SchpJ...2.3047W|doi-access=free}}</ref>

The discovery of the condition known as blindsight raised questions about how different types of visual information, even unconscious information, may be affected and sometimes even unaffected by damage to different areas of the visual cortex.<ref name="Stoerig">{{cite journal|vauthors = Stoerig P|title = Varieties of vision: from blind responses to conscious recognition|journal = Trends in Neurosciences|volume = 19|issue = 9|pages = 401–6|date = September 1996|pmid = 8873358|doi = 10.1016/S0166-2236(96)10051-5|s2cid = 25012895}}</ref> Previous studies had already demonstrated that even without conscious awareness of visual stimuli, humans could still determine certain visual features such as presence in the visual field, shape, orientation and movement.<ref name="Weiskrantz" /> But, in a newer study evidence showed that if damage to the visual cortex occurs in areas above the primary visual cortex, the conscious awareness of visual stimuli itself is not damaged.<ref name="Stoerig" /> Blindsight shows that even when the primary visual cortex is damaged or removed a person can still perform actions guided by unconscious visual information. Despite damage occurring in the area necessary for conscious awareness of visual information, other functions of the processing of these visual percepts are still available to the individual.<ref name="Weiskrantz" /> The same also goes for damage to other areas of the visual cortex. If an area of the cortex that is responsible for a certain function is damaged, it will only result in the loss of that particular function or aspect, functions that other parts of the visual cortex are responsible for remain intact.<ref name="Stoerig" />

==== Alexander and Cowey ====
Alexander and Cowey investigated how contrasting stimuli brightness affects blindsight patients' ability to discern movement. Prior studies have already shown that blindsight patients are able to detect motion even though they claim they do not see any visual percepts in their blind fields.<ref name="Weiskrantz" /> The study subjects were two patients who suffered from [[hemianopsia]]—blindness in more than half of their visual field. Both subjects had displayed the ability to accurately determine the presence of visual stimuli in their blind hemifields without acknowledging an actual visual percept previously.<ref name="Alexander and Cowey">{{cite journal|vauthors = Alexander I, Cowey A|title = Isoluminant coloured stimuli are undetectable in blindsight even when they move|journal = Experimental Brain Research|volume = 225|issue = 1|pages = 147–52|date = March 2013|pmid = 23263562|doi = 10.1007/s00221-012-3355-6|s2cid = 1738371}}</ref>

To test the effect of brightness on the subject's ability to determine motion they used a white background with a series of colored dots. The contrast of the brightness of the dots compared to the white background was altered in each trial to determine if the participants performed better or worse when there was a larger discrepancy in brightness or not.<ref name="Alexander and Cowey" /> The subjects focused on the display for two equal length time intervals and were asked whether they thought the dots were moving during the first or the second time interval.<ref name="Alexander and Cowey" />

When the contrast in brightness between the background and the dots was higher, both of the subjects could discern motion more accurately than they would have statistically through guesswork. However, one subject was not able to accurately determine whether or not blue dots were moving regardless of the brightness contrast, but he/she was able to do so with every other color dot.<ref name="Alexander and Cowey" /> When the contrast was highest, subjects were able to tell whether or not the dots were moving with very high rates of accuracy. Even when the dots were white, but still of a different brightness from the background, subjects could still determine whether they were moving. But, regardless of the dots' color, subjects could not tell when they were in motion when the white background and the dots were of similar brightness.<ref name="Alexander and Cowey" />

==== Kentridge, Heywood, and Weiskrantz ====
Kentridge, Heywood, and Weiskrantz used the phenomenon of blindsight to investigate the connection between visual attention and visual awareness. They wanted to see if their subject—who exhibited blindsight in other studies<ref name="Alexander and Cowey" />—could react more quickly when their attention was cued without the ability to be visually aware of it. The researchers aimed to show that being conscious of a stimulus and paying attention to it was not the same thing.<ref name="Kentridge et al">{{cite journal|vauthors = Kentridge RW, Heywood CA, Weiskrantz L|title = Spatial attention speeds discrimination without awareness in blindsight|journal = Neuropsychologia|volume = 42|issue = 6|pages = 831–5|year = 2004|pmid = 15037061|doi = 10.1016/j.neuropsychologia.2003.11.001|s2cid = 12837840|citeseerx = 10.1.1.719.7118}}</ref>

To test the relationship between attention and awareness, they had the participant try to determine where a target was and whether it was oriented horizontally or vertically on a computer screen.<ref name="Kentridge et al" /> The target line would appear at one of two different locations and would be oriented in one of two directions. Before the target would appear an arrow would become visible on the screen, sometimes pointing to the correct position of the target line and less frequently not. This arrow was the cue for the subject. The participant would press a key to indicate whether the line was horizontal or vertical, and could then also indicate to an observer whether or not he/she actually had a feeling that any object was there or not—even if they couldn't see anything. The participant was able to accurately determine the orientation of the line when the target was cued by an arrow before the appearance of the target, even though these visual stimuli did not equal awareness in the subject who had no vision in that area of his/her visual field. The study showed that even without the ability to be visually aware of a stimulus the participant could still focus his/her attention on this object.<ref name="Kentridge et al" />

==== "CB" and "SJ" ====
Two separate studies involving the blindsighted patients “CB”<ref name="Striemer2009">{{cite journal |vauthors=Striemer CL, Chapman CS, Goodale MA |date=September 2009 |title="Real-time" obstacle avoidance in the absence of primary visual cortex |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=106 |issue=37 |pages=15996–6001 |bibcode=2009PNAS..10615996S |doi=10.1073/pnas.0905549106 |pmc=2747232 |pmid=19805240 |doi-access=free}}</ref> and “SJ”<ref name="Whitwell2011">{{cite journal |vauthors=Whitwell RL, Striemer CL, Nicolle DA, Goodale MA |date=April 2011 |title=Grasping the non-conscious: preserved grip scaling to unseen objects for immediate but not delayed grasping following a unilateral lesion to primary visual cortex |journal=Vision Research |volume=51 |issue=8 |pages=908–24 |doi=10.1016/j.visres.2011.02.005 |pmid=21324336 |doi-access=free}}</ref> both showed that visually guided action can occur in the absence of conscious perception. CB, a 75-year-old man blind on his left side, was asked to reach with his hand towards a target while avoiding various obstacles. These were placed on both his blind side and his sighted side. Despite reporting no awareness of the placement (or even presence) of the obstacles on the blind side, he was able complete each trial without bumping into a single object.<ref name="Striemer2009" /> Similarly, SJ, a 37-year-old woman blind on her right side, was presented with objects on both sides of her vision and asked to grab them. Even when she couldn’t see the object, she proved able to scale her grasp accurately.<ref name="Whitwell2011" /> Crucially, in both studies the task was then altered slightly, introducing a two second delay between when the objects were shown and when the participants completed the task. Their prior ability to react to unseen objects completely disappeared, and they ceased to exhibit any signs of blindsight, though their performance remained mainly unaffected when it came to objects on their sighted side.<ref name="Striemer2009" /><ref name="Whitwell2011" />

Some scientists have argued that the dorsal pathway dedicated to “vision-for-action” does not store information; rather, actions are coordinated in real-time based on the visual information being received at that very moment.<ref name=":9" /> This would explain why CB and SJ were able to react to visual information presented on their blind side in real-time but not after a delay. Indeed, a conclusion of the SJ study was that action based on memory seems to rely on the ventral pathway involved in perception, in a way that action based on objects in our direct line of sight does not.<ref name="Whitwell2011" /> This was backed up by an fMRI study in which ventral stream activation usually linked to visual perception was activated by actions caried out after an 18-s delay, despite the participants being in complete darkness.<ref>{{Cite journal |last1=Singhal |first1=Anthony |last2=Monaco |first2=Simona |last3=Kaufman |first3=Liam D. |last4=Culham |first4=Jody C. |date=2013-09-06 |title=Human fMRI Reveals That Delayed Action Re-Recruits Visual Perception |journal=PLOS ONE |language=en |volume=8 |issue=9 |pages=e73629 |doi=10.1371/journal.pone.0073629 |doi-access=free |issn=1932-6203 |pmc=3765269 |pmid=24040007|bibcode=2013PLoSO...873629S }}</ref> 

==== "TN" ====
A potential weak point of case studies like the ones above is that the participants were not completely blind, and therefore it is not out of the question that their existing vision could have assisted them in some way.<ref name=":9">{{Cite book |last1=Milner |first1=David |url=https://academic.oup.com/book/4415 |title=The Visual Brain in Action |last2=Goodale |first2=Mel |date=2006-10-12 |publisher=Oxford University Press |isbn=978-0-19-852472-4 |pages=71 |doi=10.1093/acprof:oso/9780198524724.001.0001}}</ref> So a particularly noteworthy patient is a man known as “TN”, who suffered two [[Stroke|strokes]] at age 52 that resulted in the destruction of the [[Visual cortex#Primary visual cortex (V1)|primary visual cortex]] (V1) in both [[Cerebral hemisphere|hemispheres]] of the brain, and hence complete loss of (conscious) sight.<ref name=":7">{{Cite journal |last1=Pegna |first1=Alan J. |last2=Khateb |first2=Asaid |last3=Lazeyras |first3=Francois |last4=Seghier |first4=Mohamed L. |date=2005 |title=Discriminating emotional faces without primary visual cortices involves the right amygdala |url=https://www.nature.com/articles/nn1364 |journal=Nature Neuroscience |language=en |volume=8 |issue=1 |pages=24–25 |doi=10.1038/nn1364 |pmid=15592466 |issn=1546-1726|url-access=subscription }}</ref> In one famous case, researchers persuaded TN to walk down an obstacle-filled hallway, without his cane or any prior knowledge of the layout. He was able to navigate the full length of the hallway without hitting a single object, at one point even hugging the wall to get past a trashcan<ref>{{cite journal |display-authors=6 |vauthors=de Gelder B, Tamietto M, van Boxtel G, Goebel R, Sahraie A, van den Stock J, Stienen BM, Weiskrantz L, Pegna A |date=December 2008 |title=Intact navigation skills after bilateral loss of striate cortex |journal=Current Biology |volume=18 |issue=24 |pages=R1128-9 |bibcode=2008CBio...18R1128D |doi=10.1016/j.cub.2008.11.002 |pmid=19108766 |doi-access=free}}</ref><ref>{{Cite journal |last1=Ajina |first1=Sara |last2=Bridge |first2=Holly |date=2017-10-01 |title=Blindsight and Unconscious Vision: What They Teach Us about the Human Visual System |journal=The Neuroscientist |language=EN |volume=23 |issue=5 |pages=529–541 |doi=10.1177/1073858416673817 |issn=1073-8584 |pmc=5493986 |pmid=27777337}}</ref>. 

TN has taken part in a number of other experiments looking at blindsight. In one early study, he was shown images of expressive faces<ref name=":7" />. While he could not guess the gender or shape accurately, he correctly guessed what emotion was shown at an above chance level. [[Neuroimaging|Brain imaging]] showed significant activity in the right [[amygdala]], particularly in response to fearful faces, suggesting that the brain can unconsciously process expressions of emotion<ref name=":7" />.

Similarly, another experiment investigated the brain’s sensitivity to looming stimuli, which often indicate an incoming collision<ref name=":8">{{Cite journal |last1=Hervais-Adelman |first1=Alexis |last2=Legrand |first2=Lore B. |last3=Zhan |first3=Minye |last4=Tamietto |first4=Marco |last5=de Gelder |first5=Beatrice |last6=Pegna |first6=Alan J. |date=2015-10-22 |title=Looming sensitive cortical regions without V1 input: evidence from a patient with bilateral cortical blindness |journal=Frontiers in Integrative Neuroscience |volume=9 |page=51 |doi=10.3389/fnint.2015.00051 |doi-access=free |issn=1662-5145 |pmc=4614319 |pmid=26557059}}</ref>. This sensitivity can involve heightened [[attention]] capture, but is also thought to operate on a [[subconscious]] level, and has been observed in monkeys and infants<ref>{{Cite journal |last1=Ball |first1=William |last2=Tronick |first2=Edward |date=1971-02-26 |title=Infant Responses to Impending Collision: Optical and Real |url=https://www.science.org/doi/10.1126/science.171.3973.818 |journal=Science |volume=171 |issue=3973 |pages=818–820 |doi=10.1126/science.171.3973.818|pmid=5541165 |bibcode=1971Sci...171..818B |url-access=subscription }}</ref><ref>{{Cite journal |last1=King |first1=Sheila M. |last2=Cowey |first2=Alan |date=1992-11-01 |title=Defensive responses to looming visual stimuli in monkeys with unilateral striate cortex ablation |url=https://linkinghub.elsevier.com/retrieve/pii/002839329290053O |journal=Neuropsychologia |volume=30 |issue=11 |pages=1017–1024 |doi=10.1016/0028-3932(92)90053-O |pmid=1470337 |issn=0028-3932|url-access=subscription }}</ref>. In the experiment<ref name=":8" />, both TN and a group of [[Control group|control]] participants were shown a series of moving red dots, some of which made looming motions. An [[Functional magnetic resonance imaging|fMRI]] scan of the control group showed that the movement of the dots produced normal activation in the [[Visual cortex#Middle temporal visual area (V5)|middle temporal visual area]] (V5), known for its role in motion processing. In TN, activation was found in response to both general motion and to looming in particular; notably, however, this occurred primarily in areas of the brain not associated with motion processing in healthy individuals. Given that the specific V5 areas activated in the control participants were mostly [[Lesion|lesioned]] in TN, this unusual activation seems to be a result of [[Neuroplasticity|cortical plasticity]]<ref name=":8" />.

==== Other cases ====
Other cases refer to SL, GY and GR.<ref name=":4" />