Ability to perform tasks based on vision without awareness of vision.
Blindsight is a phenomenon in which people who are perceptually blind in a certain area of their visual field demonstrate some response to visual stimuli.
]In Type 1 blindsight subjects have no awareness whatsoever of any stimuli, but yet are able to predict, at levels significantly above chance, aspects of a visual stimulus, such as location, or type of movement, often in a forced-response or guessing situation.
Type 2 blindsight is when subjects have some awareness of, for example, movement within the blind area, but no visual percept. This may be caused by, for example, the person being aware of their eyes' tracking motion which will function normally. Blindsight is caused by injury to the part of the brain responsible for vision (see occipital lobe). Evidence for it can be indirectly observed in children as young as two months, although it is difficult to determine the type in a person who is not old enough to answer questions
DB- underwent surgical removal of malformation in pole of right occipital lobe (V1), became blind in left hemifield (normal vision in right) and had no conscious experience of any visual sensation in damaged field. Larry Weiskrantz et al 1974 created the term blindsightedness to explain his condition.
He was tested using a perimeter- is a hemisphere (diameter 60 cm) to the surface of which a light spot can be reflected as a visual target.
Was not aware of seeing moving of flashing lights but when asked to move eyes to target was slightly above chance, and when asked to point to target with hand was very much above chance thus blind field was almost as good as normal field for pointing.
"D.B. could not see one’s outstretched hand but seemed able to reach for it accurately."
Patient GY- Graham Young
Studies of blindsight have been largely based on a single patient, GY.GY became hemi-blind (suffered blindness in his right visual field) following damage to V1 of one hemisphere in a car accident at the age of seven. Specifically was missing most of his left striate cortex.
Two Visual Streams
As visual information follows two main channels, or "streams". The....
Dorsal Stream- bottom-up action (not conscious) proposed to be involved in the guidance of actions and recognizing where objects are in space. Also known as the parietal stream, the "where" stream, or the "how" stream, this pathway stretches from the primary visual cortex (V1) in the occipital lobe forward into the parietal lobe. It is interconnected with the parallel ventral stream (the "what" stream) which runs downward from V1 into the temporal lobe.The dorsal stream is involved in spatial awareness and guidance of actions (e.g., reaching). In this it has two distinct functional characteristics—it contains a detailed map of the visual field, and is also good at detecting and analyzing movements.
Ventral Stream-top-down seeing (Cognitive,Conscious) is associated with object recognition and form representation. It has strong connections to the medial temporal lobe (which stores long-term memories), the limbic system (which controls emotions), and the dorsal stream (which deals with object locations and motion).
Evidence for the two Steam hypothesis- Patient DF
Patient DF- Milner and Goodale (1985)- DF suffered from hypoxia caused by monoxide poisoning. MRI in 1989 showed diffuse cortical damage with large lesions in the ventrolateral occipital region, sparing VI.
Symptoms- unable to identify shape of objects, objects recognised by colour, ability to identify shades of the same colour and texture, unable to identify boundaries of overlapping objects of with similar colour or texture
Main Symptom- Visual Form Agnosia
Visual Form Agnosia- is the inability of the brain to make sense of or make use of some part of otherwise normal visual stimulus and is typified by the inability to recognize familiar objects. Gives evidence for the Two Streams Hypothesis, as the patient can see the object and its position (Dorsal Stream intact) but cannot fails with object recognition (Suggests the Ventral Stream is affected by lesions shown in MRI).
Evidence for Two Streams- Optic Ataxic patients IG
IG and RV showed opposite symptoms to DF.
Optic ataxia (lack of coordination between visual inputs and hand movements, resulting in inability to reach and grab objects. Optic ataxia may be caused by lesions to the posterior parietal cortex. The posterior parietal cortex is responsible for combining and expressing positional information and relating it to movement.
IG- Suffered lesion to the posterior parietal cortex bilaterally.
RV-Suffered bilateral damage to parietal lobe
Shows that they suffered damage to their Dorsal Stream.
Two main speech disorders- Broca's aphasia
The Broca's area of the brain is located in the left inferior frontal lobe and contains programmes of articulation. Damage to this area leads to symptoms such as...
1.) slow, laborious, non-fluent speech
2.)difficulty with function words (if and as), however content words remain ok (nouns and verbs)
Broca's aphasia typically characterised by 1.) Agrammatism- problems with gramma 2.) Anomia (word finding difficulties) 3.) Articulation difficulties (likstip for lipstick)
They frequently speak in short phrases that make sense but are produced with great effort. They often omit small words such as “is,” “and,” and “the.” For example, a person with Broca’s aphasia may say, “Walk dog,” meaning, “I will take the dog for a walk,” They understand others speeck well so get easily frustrated.
Wernicke's area is located in the posterior region of the brain and is involved in comprehending language.
Damage to this area may result in...
1.)Loss of ability to understand speech,
2.)but speech production is still fluent
3.)sounds meaningfull because intonation is still good.
People with Wernicke’s aphasia may speak in long sentences that have no meaning, add unnecessary words, and even create made-up words.As a result, it is often difficult to follow what the person is trying to say. People with Wernicke’s aphasia usually have great difficulty understanding speech, and they are often unaware of their mistakes.
Disorder of Face perception- Prosopagnosia
Prosopagnosia (Greek: "prosopon" = "face", "agnosia" = "inability to recognize/identify") is a disorder of face perception where the ability to recognize faces is impaired, while the ability to recognize other objects may be relatively intact. The term originally referred to a condition following acute brain damage, but recently a congenital form of the disorder has been proposed, which may be inherited by about 2.5% of the population. The specific brain area usually associated with prosopagnosia is the fusiform gyrus
There are three main forms of prosopanosia....
1.)Developmental prosopagnosia (DP) is a face-recognition deficit that is lifelong, manifesting in early childhood, and that cannot be attributed to acquired brain damage. However, a number of studies have found functional deficits in DP both on the basis of EEG measures and fMRI. It has been suggested that a genetic factor is responsible for the condition.
Three Main forms of Prosopagnosia
2.) Apperceptive prosopagnosia is a disorder of some of the earliest processes in the face perception system. People cannot make any sense of faces and are unable to make same-different judgments when they are presented with pictures of different faces. Unable to work out age/gender of person from face, recognise people on the basis of non-face clues i.e clothing
3.) Associative prosopagnosia is thought to be an impairment to the links between early face perception processes and the semantic information we hold about people in our memories. People with this form of the disorder may be able to say whether photos of people's faces are the same or different and derive the age and gender from a face. but may not be able to subsequently identify the person or provide any information about them such as their name, occupation, or when they were last encountered them.
LH- Prosopagnosia Case Study
LH was well-educated professional man who acquired prosopagnosia after a car accident. LH suffered severly with the disorder, he was unable to reliably recognise his wife, children and even himself in group photographs.
Farah, Levinson and Klein (1995) studied LH using the recognition memory paradigm. Normal subjects and LH were given a set of photos which were a mixture of face and non-face objects i.e spoons, chairs etc. Then the subjects were given a larger set of photos and asked if old or new, normal subjects performed equally well with face and non-face objects whereas LH showed a significant performance disparity performing worse with faces than with objects,
Korbinian Brodmann was a German neurologist who became famous for his definition of the cerebral cortex into 52 distinct regions from their cytoarchitectonic (histological) characteristics.Brodmann areas have been discussed, debated, refined, and renamed exhaustively for nearly a century and remain the most widely known and frequently cited cytoarchitectural organization of the human cortex.Many of the areas Brodmann defined based solely on their neuronal organization have since been correlated closely to diverse cortical functions. For example, Brodmann areas 1, 2 and 3 are the primary somatosensory cortex; area 4 is the primary motor cortex; area 17 is the primary visual cortex; and areas 41 and 42 correspond closely to primary auditory cortex. Higher order functions of the association cortical areas are also consistently localized to the same Brodmann areas by neurophysiological, functional imaging, and other methods However, functional imaging can only identify the approximate localization of brain activations in terms of Brodmann areas since their actual boundaries in any individual brain requires its histological examination.
Theories of Depression- Becks (1976) cognitive the
According to Beck's theory of the etiology of depression, depressed people acquire a negative schema of the world in childhood and adolescence; children and adolescents who suffer from depression acquire this negative schema earlier. Depressed people acquire such schemas through a loss of a parent, rejection by peers, bullying, criticism from teachers or parents, the depressive attitude of a parent and other negative events. When the person with such schemas encounters a situation that resembles the original conditions of the learned schema in some way, even remotely, the negative schemas of the person are activated. Beck's negative triad holds that depressed people have negative thoughts about themselves, their experiences in the world, and the future.For instance, a depressed person might think, "I didn't get the job because I'm terrible at interviews. Interviewers never like me, and no one will ever want to hire me." In the same situation, a person who is not depressed might think, "The interviewer wasn't paying much attention to me. Maybe she already had someone else in mind for the job. Next time I'll have better luck, and I'll get a job soon." Beck also identified the following cognitive distortions, which can contribute to depression: arbitrary inference, selective abstraction, overgeneralization, magnification and minimization.
Neurological theory of depression
Neuroimaging studies have found consistent abnormalities in at least four areas of the brain in people with depression: the prefrontal cortex, anterior cingulate, hippocampus, and amygdala.
Critical functions of the prefrontal cortex include attention, short-term memory, planning, and problem-solving. Damage to the hippocampus could be the result of chronic arousal of the body's stress response.
People with depression show chronically high levels of the hormone cortisol.
Abnormalities in the structure and functioning of the amygdala also are found in depression.
The amygdala helps direct attention to stimulae that are emotionally salient and have major significance for the individual.