Another compelling example is the rat/man illustration (b) (image here?). When you perceive the rat, you are, effectively, agnosic for the man, and vice versa. For normal people, it is a bistable figure; but for John, perception of neither rat nor man would ever occur, despite his normal visual acuity.
You can also get a feel for agnosia by thinking of what happens when you listen to a foreign tongue. You hear all the sounds, syllables, intonations and rhythms of the speech, but none of it makes any sense to you (c) (image?). You simply cannot create a meaningful perception from these sensations.
Problems in the Pathways
To understand GY’s and John’s predicaments, we will need to take a brief tour through the anatomy of the visual pathways. Those more than 30 visual-processing areas have staggeringly complex connections among them. Fortunately, despite this complexity, we can discern a simple overall pattern.
Messages from the retina of the eye get transmitted along the optic nerve before diverging into two parallel anatomical pathways, which we shall call “old” and “new” pathways to indicate their evolutionary sequence (d). The old pathway, also called the where pathway, goes to a structure called the superior colliculus, which forms a bump on the roof of the brain stem, the stalk that emerges from below the brain and continues as the spinal cord. The colliculus helps to determine the location of an object. When a novel or salient event occurs in your environment (for example, when there is an object looming over your left shoulder), you reflexively orient and swivel your eyeballs toward it without knowing what it is. That is, you orient to it or locate it before you proceed to identify it.
The other pathway, the newer one, as we shall see, is required for identifying an item, even though it is incapable of locating it or orienting to it. The new pathway projects to the visual cortex (V1 for short) in the back of the brain, where the features of the object are analyzed (for color, orientation of edges, movement, and so on). Information from V1 splits again into two pathways farther along the visual-processing course: the how pathway projecting into the parietal lobes (“How” do I use or interact with this object?) and the what pathway (“What” exactly is this object? What does it mean for me?) into the temporal lobes (d). The 30 visual areas we spoke of are shared between these pathways. Bear in mind that we have described a grossly oversimplified caricature: many fibers go back and forth between the areas; they are heavily interconnected and not entirely autonomous. But in science it is not a bad idea to start with a simple picture.
Now let us return to GY, who has blindsight. GY has complete damage to V1. No information reaches either the what or how pathway, rendering him blind in the sense that he cannot consciously see objects. But because his where pathway (going through the superior colliculus and bypassing the damaged V1 en route to higher cortical centers) is intact, he can guide his hand unerringly toward the light spot that he cannot consciously see. It is as if there is an unconscious zombie trapped in him that can point accurately even though the conscious person is oblivious. The paradox of blindsight is resolved.
A curious philosophical implication of all this is that only the new pathway is “conscious”; the old pathway can go about its business without consciousness creeping into it. Both pathways are composed of neural circuits, but only one of them (as far as we can tell) is conscious. Scientists have no idea why, although being linked to tasks such as language and meaning might be important. Activity in the what pathway eventually evokes a verbal label or name (“mother”) and nuances of emotions however pronounced (“terror”) or subtle (“warmth”).
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7 Comments
Add CommentI wonder if it's possible that the "where" pathway developed separately from the "how" pathway in the visual cortex and that it functions on an unconscious level as an evolutionary adaptation. I could see the advantage in a threatening situation where having the brain begin to react to a potential threat by knowing where it's located and preparing a physiological response unconsciously would come in handy, rather than waiting for interpretation as to what the object is and how to interact with it. Perhaps the organization is useful in the way that the automatic withdrawal reaction is useful when touching a hot stove. You don't have to think about it, you just do it. Perhaps knowing where something is regardless of whether you know what it is proves useful for the same reason.
Reply | Report Abuse | Link to thisProof that all we sense is illusion can be seen in amputees, that have sensation in parts of missing limbs. How our brains can project an illusion of our surroundings OUTSIDE of us is a constant cause of fascination. When we turn our heads, our environment is detected as standing still. It will be a long time before we are able to program such sensing phenomena into robots!
Reply | Report Abuse | Link to thisi also have a blind sight disoderor visual blind sight disorder
Reply | Report Abuse | Link to thisi was watching discovery then i came to know that i have visual blind sight disorder in which a person is dong his functioning by watching the object if dont see the object i cannot do any thing.it is a risk factor for me in the scence of driving walking jams mostly tel me how can i prevent my self from blind sight dissorder this is mostly due to the defficiency of oxygen in the neurons or nerve cells nerve ceels are not active due to the defficency of oxygen. i m also a biologist.
I'd like to ask professor Ramachandran
Reply | Report Abuse | Link to thisa) if he thought consciousnee could be a spandrel of language (eg language mapping out the synthesis of long to short memories along such a route that they effectively produce a 'film' embedded within the none conscious operations of the body
b) do you think these conscious routes could be closely tracked by synesthetic connections so that particular memories associated with particular synesthetic 'landmarks' or neural connections stimulate or intensify the neural signals associated with 'multi-tasking' neural connectivity. So meaning is given to those neural events which tie together different sense perspectives of one activity.
Language being the locus of synesthetic connectivity between the senses. So a multiple of senses can find meaning in one symbol.
Or that correspondence between the neural locations(shared between sensory pathways) responsible for synesthetic correspondence i.e those neurons (in different sensory pathways) responsible for corepresenting the same object or action, collectively act as a 'switch' so to 'grab' an action or object and place it in either a conscious or sub or none conscious realm.
Reply | Report Abuse | Link to thisIn the conscious realm these signals resultant from the collective neuronal output are subsequently amplified and dissociated in such a way that a linguistic representaion is evoked. These pathways or associations being available for linguistic report.
Whilst the unconscious pathways are not so although synesthetic connectivity still allows control of the bady and its actions.
I argued that such human consciousness first arose with the use of portable mirrors or highly reflective surfaces whereby neuron systems were tuned accurrately so that these processes were first accurately coordinated through sensory feedback.
(Peter Reynolds - Didd Mirrors Cause Consciousness Tucson 2010).
Thinking on the hoof here - is it possible that deafness would have not been too big a disadvantage in the absence of language and might even have been an advantage in producing or enhancing a gesturally based language - so might have been tolerated earlier than blindness.
Reply | Report Abuse | Link to thisWould certain neural pathways have become unmasked in these individuals and when blindness came along as an 'allowable' disability, the interbreeding between the deaf and blind would cause synesthesia in the unmasked neurons associated with the enhance abilities seen in the deaf and blind.
Would this correspond to the 'new' or 'conscious' visual pathway described by Vilayanur Ramachandran and others or provide as specific type of feed into an older pathway so to distinguish it from what is now regarded as the older pathway.
These 'newer' neural pathways being associated with langauge in particular because it was the deaf in whom language was most clearly defined from a visual perspective.
Likewise this newer pathway would become more enhanced in offspring of the deaf and blind.
These pathways becoming unmasked in the general population according to the templates of cave art, whose narrative would instantiate and carve out routes that would lead to consciousness.
Being finally fully embedded with the use of mirrors and the constructive feedback from mirror use.
peter reynolds
reflectogenesis@hotmail.co.uk
Sorry the above was out of context.
Reply | Report Abuse | Link to thisI am postulating that consciousness came about from the interbreeding of the deaf and blind 50000 years ago which I am suggesting is the first time society had gained control of its evironment for the first time enough to support - firstly deaf (as this would not have been too great a disability given that language might not have existed) - and then the blind.
Bavalier et al suggesting that the remaining sense modalities in the deaf and blind are enhanced as compared to normally sensed humans)
Peter Reynolds
Reflectogenesis@hotmail.co.uk