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z3291629 - Petya Arabadzhiyska
z3289041 - Dylan Vitucci
z3291155 - Rhys Mitchell
z3287905 - James Dunn

Introduction



Consciousness is a phenomenon which still eludes complete scientific definition and understanding. However, some rare and fascinating conditions have allowed scientists to begin to uncover the mystery of how the human brain works and what it means to be conscious. One such phenomenon is a condition known as ‘Blindsight’. Blindsight is a broad term which essentially describes a neurological condition in which people that are partially or completely blind can still respond to some visual stimuli despite no conscious awareness of being able to see anything at all. This implies that an unconscious component of the human brain is (to an unknown extent) a contributor to our behaviours, even in the case of vision which many would regard as a solely conscious process. The link between blindsight and consciousness is one of the factors which made blindsight an intriguing and important topic for our group.

We chose this topic not only because of its intriguing nature in relation to consciousness but also because of its potential to help explain the neuroscientific basis of vision, attention and the neural pathways and brain regions involved. The media item we selected to represent blindsight is a video excerpt from the documentary ‘Phantoms in the brain’ presented by Dr Ramachandran. This video was chosen because it introduces the concept of blindsight in a simple yet interesting manner. It is neither too vague nor too detailed so it allows room for individuals to make their own inferences based on the sufficient amount of information given.


Media Item






Blindsight: A Definition



Blindsight is the visual phenomena where an individual has the ability to depict visual information although they are not entirely conscious of the experience. An individual that suffers from blindsight is said to have residual visual capacity in which they are still able to identify and pinpoint objects though without being aware. Blindsight can, therefore, be clinically defined as the "Visual Capacity in a field defect in the absence of acknowledged awareness"(Weiskrantz, 1986). Recent Studies have helped to redefine the explanation of Blindsight and designate the origin of the impairment to be associated with extensive damage to the Primary Visual Cortex. Factors such as lesions and strokes are generally the contributing causes.

Previously blindsight was only reported in people with partial damage to the visual lobes however recent studies that showed that it can occur even when both visual lobes are completely destroyed, like the in the clinical study of patient T.N. who is suffered complete loss to both visual lobes but still successfully navigated a corridor of obstacles while not being aware they were even there.

Neuroscience Context



Subtypes

'Phantoms in the brain' only draws attention to one particular type of blindsight. There are however many other ones which are noted in the literature.

Initially, Weiskrantz split blindsight into 2 main types, Type 1 and Type 2:
Type 1 The patient is completely unaware of any stimuli in their dead field. Yet, they are able to guess at a higher than chance rate what sort of things are there, such as location, or direction of movement. Despite having no concious percept of what they are 'seeing'.
Type 2
This involves the patient being aware that something is within their blind field without being able to see it. They will usually state they can 'feel' something there or know that their eyes are tracking. (Weinskrantz)

Now, whilst these definitions are perfectly suitable, there are more complex things happening, and as such they have been split up again.

Action Blindsight

This is being able to either saccade or point at an item within the visual feild whilst having no concious precept of this. It is hypothesised that the superior culliculus is responsible for this ability (Gaymard and Pierrot-Deseillingy, 1999). This is due to the visual circuitry being split into many parallel pathways as it travels along. The visual cortex and the superior culliculus are running off seperate pathways and in different parts of the brain. This explains why when the cortex is damaged, this form of 'sight' is still possible.Studies have proven this using patients who have little to no cortex left in one hemisphere, who are still able to localise to the targets in their blind field (Ptito et al., 1991).


Attentional blindsight

In comparison, patients have an awareness or a sense that something being within their blind field despite not having any visual perception. This is better known as the Riddoch Phenomenon (Morland et al., 1999) This ability may be related to alerting functions along with the V5 area in the brain which is known to help process visual motion (Dukelow et al., 2001). Activation in relation to both ipsilateral and contralateral motion has been found in this area, which supports this hypothesis (Dukelow et al., 2001).

These two types are incredibly similar and may rely on the same neural pathway. However, one can be present without the other and it depends on the type of test used to determine which it is.(Danziger et al., 1997)


Agnosopsia

This involves the patient being able to guess the perceptual characteristics of an item with no perceptual awareness at all, such as differentiating between different wavelengths or forms. This term was coined by Zeki and Ffytche, (1998). One reason for why this happens is suggested to be due to this running off an entierly different set of neural pathways from both attention and action blindsight (Danckert & Rossetti, 2005)

The main distinction between angosoposia and action blindsight is in the behaviours demonstrated and how these are tested for as opposed to a direct comparison between awareness and behaviour. The main point overall though, is that these three are likely to rely on different neural pathways (Danckert & Rossetti, 2005).

Pegna (2005) also investigated the phenomena of emotional blindsight, where blind patients are able to detect the emotion expressed on faces but not perceived other information such as their identity or gender. Pegna presented with images of fearful faces to participants who then cringed subconsciously despite not being able to consciously see the faces.This suggests that the neurological pathways involved in blindsight not only register solid objects but also are able to unconsciously process strong social signals.

Pathways of Blindsight


According to Ramachandran, blindsight is a result of brain damage to one of two pathways involved in transmitting information from eye to brain. The first pathway is evolutionarily older and more primitive. Here, information goes from the eye to the brain stem. The other pathway is more complicated and involves information travelling from the eye to the thalamus then to the visual cortex where it is integrated and interpreted. Ramachandran believes that blindsight occurs when signaling from the eye to the visual cortex is damaged but the pathway to the brainstem is still intact. In other words, visual information is detected by the brainstem but it is not recognized as being present because the higher brain centre responsible for visual consciousness is not receiving input. Although research into blindsight is yet to determine the underlying neural structure,there is evidence that the brainstem does play a vital role.

The superior colliculus is a brain structure located in the midbrain of the brainstem. Whilst the superior colliculus' role is more prominent in other animals then mammals, who rely more on the visual cortex for information, it remains an important underlying part of functioning, controlling various visual functions such as eye movements. However is has been showed that "this area of the midbrain is essential for translating a visual signal that cannot be consciously perceived into action" (De Gelder, 2010).

In an experiment by De Gelder (2010) visual stimulus to participants that were blind to one half of their visual field. The stimulus was either gray or a specific shade of purple which the superior colliculus is known to be blind too. Brain scans during this experiment highlight the activity of only the superior colliculus and not other areas of the midbrain when they exhibited blind sight as predicted, only to the gray stimuli and not the purple stimuli. The findings of this experiment highlight the superior colliculus in blindsight as it acts as a separate pathway for visual information and processing to the visual cortex and contributing to the subsequent motor responses outside conscious awareness. The superior colliculus is also suspected to the involved in emotional blindsight along with other areas of the midbrain such as the amygdala, which registers emotion.


blindsight.jpg
Figure 1. Yellow area indicates primary visual pathway to the occipital lobe while the blue area indicates the unconscious pathway to higher processing areas through the superior colliculous

Implications of Blindsight


On a deeper level, Blindsight has also contributed to the notion that the human brain can and does respond to environmental stimuli without our conscious awareness. Ramachandran likens blindsight to the act of driving a car, avoiding hazards and responding to avoid dangerous situations all of which can be done subconsciously whilst having a conversation. Given these observations, it is possible to infer that one dimension of consciousness is simply the act of being aware. Unlike the driving scenario however, Blindsight patients cannot intentionally shift their attention. Nevertheless, evidence for the existence of a subconscious visual pathway gives rise to the possibility that perhaps some day, Blindsight sufferers may be able to become ‘aware’ of the visual cues. The neurological pathway through the superior colliculus could be exploited through training to aid in day to day navigation for cortex-based vision loss suffers. With time and practice people with these injuries may learn to use these pathways and reduce reliance on other aid such as a cane or guide dog but also possibly gain some conscious vision too.


Media Item Analysis



The media item is an excerpt of the documentary 'Phantoms of the Brain' derived from the book by Dr V.S Ramachandran of the same name. The program was televised on the BBC and focuses on the phenomena of blindsight. It features expert analysis by Dr. Ramachandran, a renowned neurologist and leader in research surrounding visual perception and neurology, whose insightful and credible inputs ensure the program remains reliable but also to the point.

The documentary tries to focus on reaching the general population which is evident as the program was broadcasted on the BBC. The aim of the program is to be both informative and entertaining but at the same time simplistic with its explanations of the topic. Individuals with a vested interest in neurology would benefit far greater from viewing this documentary as it is more appealing and also those familiar with the work of Ramachandran. Insights from Dr Blakemore, a neurobiologist specialising in vision, and the focus patient Graham enable the documentary to explain efficiently and appropriately the impairment of blindsight to the wider audience. Therefore it was easy to determine that the content of the media item would be credible.

The excerpt follows the patient Graham, who although is clinically blind on his right side, is able to describe movements in his impaired visual field. Throughout the excerpt we are able to experience and identify the difficulties Graham has faced with his impairment in everyday life. The program then becomes intriguing by coinciding a visual test conducted on Graham. The task involved different menial tasks that involve the patient identifying the direction of an object on a computer screen in his impaired visual field. What is even more astounding is that Graham is able to guess the direction more correctly then if by random chance. From this the audience is able to witness first-hand the mystery of the blindsight condition.

The utilisation of language within the excerpt is crucial to the documentary reaching its wider audience. The animated Ramachandran enthusiastically draws people in with his explanations using layman terms but at the same time intrigues the audience by encouraging self-thought processing. Statements from Dr Blakemore help to emphasise the extraordinary behaviour individuals with blindsight exhibit and the potential it has to unlock previously unexplained occurrences involving the brain. The conviction by which Ramachandran boldly suggests his theories enable the viewer to believe that his proposals ‘make sense’ as his manner is both entertaining and intriguing which engages the audience.

The limitations of the documentary include neglecting previous research into blindsight. It ignores efforts made by profound neurologists and predominantly focuses on the theory proposed by Ramachandran. Within the documentary, Ramachandran suggests within our brain there are two visual pathways working in parallel. The prominent more recognised pathway is considered to be an evolutionary adaptation by where visual information is received via the eyeball and transferred to the thalamus. Ramanchandran further explains that the second pathway constitutes reflexive behaviour, therefore accentuating his theory on blindsight by where both pathways are interrupted but it is the second pathway that enables a person who experiences blindsight to recognise movements in their otherwise impaired visual field. Another theory that has been proposed on numerous occasions though recently explored thoroughly in a study conducted by Radoeva et al in 2008 is that “islands” of preserved V1 may mediate spared vision” (Radoeva, Prasad, Brainard and Aguirre, 2008). This means that although damage to the V1 cortex has occurred small areas are still functioning hence contributing to the individuals residual vision. The patient was subjected to a test and was able to discriminate and identify stimuli presented to the “island”, however, the patient “never saw anything” despite a sense that “something happened there” (Radoeva, 2008). This attributes to Type II blindsight which was not discussed in Ramachandran’s hypothesis, as his view only portrayed blindsight as a whole entity.

Overall the excerpt is informative and entertaining while still holding true to its neurological background. In regards to aim of the program, in reaching its target audience, it has conducted this successfully by providing an adequate and engaging explanation to blindsight. However, as a research tool its inability to connect with other research conducted on blindsight limits the usefulness and validity of this program. This is due to the vast array of theories proposed on blindsight without a clear understanding still to be found. Through this a response can be elicited from the neurological world and those with previous knowledge on the topic to debate and then potentially define, through collective reasoning, an appropriate definition of blindsight.


Search Strategies



Blindsight was briefly mentioned in both the lectures and tutorial and seemed like an interesting phenomena to research for this project. We began by searching for blindsight neuroscience videos on both Google videos, a large video search engine, and Youtube, the largest video hosting website online. The first result relevant result brought up by both searches was this excerpt from the documentary "Phantoms in the Brain." We had previously seen part of this documentary that features Dr Ramachandran in the tutorials and found this excerpt both interesting and informative. We also discovered through further research that this is the most frequently referenced documentary on blindsight as a valid source of information. The documentary is as recent as 2008 and features the animated Dr Ramachandran is cited as "one of the world's foremost brain researchers" by Dr. Francis Crick who is a distinguished Research Professor from the Salk Institute Nobel Laureate.


References



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2. De Gelder, B. (2010). Uncanny Sight in the Blind. Scientific American. 302(5), 60-65. Link

3. Dukelow et al. (2001), Distinguishing Subregions of the Human MT+ Complex using Visual Fields and Pursuit Eye Movements, Journal of Neurophysiology. 86,1991–2000. Link

4. Danckert, J. & Rossetti, Y. (2005). Blindsight in Action: What can the Different Sub-types of Blindsight tell us about the Control of Visually Guided Actions?". Neurosci Biobehav Rev 29 (7), 1035–1046. doi:10.1016/j.neubiorev.2005.02.001

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7. Pegna, A.J, Khateb, A., Lazeyras, F. & Seghier, M.L. (2004). Discriminating Emotional Faces without Primary Visual Corticies involves the Right Amygdala. Nature Neuroscience. 8(1), 24-25. doi:10.1038/nn1364

8. Ptito et al. (1991). Target Detection and Movement Discrimination in the Blind Field of Hemispherectomized Patients, Brain: A Journal of Neurology. 114, 497–512. doi: 10.1093/brain/114.1.497

9. Radoeva, P. Prasad, S. Brainard, D. Aguirre, G. (2008): Neuronal Activity within Area V1 reflects Unconscious Visual Performance in a Case of Blindsight. Journal of Cognitive Neuroscience. 20 (11), 1927-1939. doi: 10.1162/jocn.2008.20139

10. Weiskrantz, L. (1986). A Case Study and Implications.Oxford: Oxford University Press

11. Zeki S, Ffytche DH (1998) The Riddoch syndrome: Insights into the Neurobiology of Conscious Vision. Brain: A Journal of Neurology. 121:25–45. doi: 10.1093/brain/121.1.25