1.3 To link lesions of the parietal and occipital lobes to motion and perception disorder Flashcards
Two key elements in the way the brain organises the visual fields
Kolb&Wishaw H13
- The left half of each retina sends projections to the right sight of the brain, right half sends its projections to the left side of the brain. The representation of each side of the visual world seen by each eye is sent to the same place in area V1, and damage to V1 affects vision in both eyes.
- Different parts of the visual field are represented in different parts of area V1. Thus, injury to a specific region of V1 produces a loss of vision in a specific part of the visual world.
PLAATJE met verschillende soorten blindness.
monocular blindness
Kolb&Wishaw H13
Due to destruction of the retina or optic nerve of one eye –> which is the loss of sight in that eye.
Bitemporal hemianopia
Kolb&Wishaw H13
Lesion of the medial region of the optic chiasm severs the crossing fibers –> the loss of vision of both temporal fields.
Buitekanten van visueel veld, dus rechts-rechts en links-links
This dificit can occur when a tumour develops in the pituitary gland. As the tumour grows, it can put pressure on the medial part of the chiasm and produce the loss or disurbance of lateral vision.
Nasal hemianopia
Kolb&Wishaw H13
A lesion of the lateral chiasm –> results in a loss of vision of one nasal field
Homonymous hemianopia
Kolb&Wishaw H13
Complete cuts of the optic tract, lateral geniculate body or area V1 –> which is the blindness of one entire visual field.
Dus bv 2 keer aan linkerkant waardoor je heel visueel veld mist
In field 5 the disturbance affects info coming from both eyes, because of this we know that the visual field defect is present in both eyes.
Quadrantopia
Kolb&Wishaw H13
Lesions in the eye or optic tract –> produce visual disturbance in one eye.
Lesions to the optic nerve or brain affect both eyes. If lesion is partial only a part (quadrant) of the visual field is destroyed.
Macular sparing
Kolb&Wishaw H13
Helps to differentiate lesions of the optic tract or thalamus from cortical lesions because macular sparing occurs only after unilateral lesions to the visual cortex.
Macular sparing does not always occur, however, many people with visual-cortex lesions have a complete loss of cision in one-quarter or one-half of the fovea.
macular= gele vlek
Scotomas
Kolb&Wishaw H13
Are small blind spots in the visual field, produced by small occipital lobe lesions.
People are often totally unaware of scotomas because of constant tiny involuntary eye movements and “spontaneous filling in” by the visual system.
Visual agnosia
Kolb&Wishaw H13
Difficult to describe due to the variety of pat’s and the lack of agreement on the taxonomy.
We seperate visual agnosias into object agnosias and other agnosias.
Visual object agnosia
Kolb&Wishaw H13
Distinguishes 2 broad forms:
1. Apperceptive agnosia
2. Associative agnosia
Visual object agnosia
Apperceptive agnosia
Kolb&Wishaw H13
Failure of object recognition in which basic visual functions (colour and motion) are perserved.
Fundamental deficit: inability to develop a percept of the structure of an object or objects.
Simultagnosia: pat’s can perceive the basic shape of an object, but they can’t perceive more than one object at a time. So, if 2 objects are presented together, only one is perceived.
Apperceptive agnosia doesn’t result from a restricted lesion but usually follows gross bilateral damage to the lateral parts of the occipital lobes. including regions sending outputs to the ventral stream.
Visual object agnosia
Associative agnosia
Kolb&Wishaw H13
Inability to recognize an object despite its apparent perception. Thus, the associative agnosic can copy a drawing rather accurately, indicating a coherent perception, but cannot identify it.
Associative agnosia is more likely with damage to regions in the ventral stream that are farther up the processing hierarchy, such as the anterior temporal lobe.
Other visual agnosias
Kolb&Wishaw H13
- Prosopagnosia
- Alexia
- Visuospatial agnosia
Porspagnosia
Kolb&Wishaw H13
Pat’s cannot recognize any previously known faces, including their own as seen in a mirror or photograph. They can however recognize people by face information, birthmark, moustache, characteristic hairdo.
(They may not accept that they don’t recognize themselves in the mirror, probably because they know who must be in the mirror and thus they see themselves.)
Most facial agnostics can tell humans from nonhuman faces and can recognize facial expression.
Due to bilateral damage centred in the region below the calcarine fissure at the temporal junction.
These findings indicate that facial recognition is probably a bilateral process, but assymetrical.
Alexia
Kolb&Wishaw H13
Inability to read. Often a symptom complementary to facial-recognition deficits.
Most likely to result from damage to the left fusiform and lingual areas.
It can be conceived as a form of object agnosia, in which there is a perceptual inability to construct wholes from parts, or as a form of associative agnosia in which word memory is either damaged or inaccessible.
Visuospatial agnosia
Kolb&Wishaw H13
Topographic disorientation, in this condition the pat had the inability to find one’s way around familiar environments uch as one’s neighbourhood.
The critical area for this disorder lies in the right medial occipitotemporal region, including the fusiform and lingual gyri.