Learning III Flashcards
What are the key details of the visual field?
- Full horizontal range is just over 180 degrees
- Horizontal range in one eye is 160 deg (60 deg nasal field; 100 deg temporal field)
- Vertical range 135 deg. (60 deg upper field; 75 deg lower field).
What visual field deficits can be produced by lesions in the visual pathway?
- Lesion of right optic nerve causes total vision loss in right eye.
- Lesion of optic chiasm causes bilateral hemianopia.
- Contralateral hemianopia (complete loss of vision in temporal halves)
- Meyer’s loop (lesion of optic radiation) upper contralateral quadratic anopia)
- Partial visual cortex lesions leads to partial visual field deficits in opposite sides.
What is blindsight? (Weiskrantz 1986)
Where a patient has some residual visual sensitivity without visual consciousness.
What is prosopagnosia and what causes it?
This is ‘face blindness’, whe. a person cannot recognise any faces. Can be acquired or hereditary. Lesion to fusiform gyrus in ventral stream (right hemisphere).
What is cerebral akinetopsia?
This is termed ‘motion blindness’, when the patient cannot perceive any visual motion following a lesion to extrastriate cortex (V5). Case study - L.M.
What is visual agnosia?
This is an impaired ability to visually recognise objects (apperceptive and associative) caused by damage to the ventral stream.
What is cerebral achromatopsia?
This is colour blindness caused by damage to the visual cortex in V4.
What is Balint’s Syndrome?
This is an inability to perceive the visual field as a whole, resulting in difficulty in fixating the eyes, and inability to move hand towards an object under visual guidance.
What are the two phases of brain injury development?
Phase 1: Primary injury: direct tissue damage, impaired brain blood flow, impaired metabolic activity which leads to edema and changes to cytoarchitectural changes.
Phase 2: secondary injury: loss of cell homeostasis, calcium and sodium ion release, neurotransmitter release, excitotoxicity and break-down of blood brain barrier - leading to cell death.
What are the stages of plasticity following visual brain injury?
This is a two-stage process;
1. spontaneous recovery: diaschisis reversal, kinematics changes and cortical reorganisation.
2. training-induced recovery: recruitment and retraining of residual brain areas and compensation
What is visual restoration therapy (VRT) and how has it been used to rehabilitate visual deficits post-injury?
VRT requires participants to detect a bright light on a monitor in one of 500 locations on border between blind and sighted fields. It can help improve detection accuracy and reduce the size of the blind field and increase size of visual field (Kasten, Wust, Behrens-Baumann & Sabel 1998)
How can dot motion discrimination be improved after stroke-induced damage to V1?
Huxlin et al., (2009) found that training adults with this stroke damage to V1 to discrimination direction of dot motion allowed them to recover the ability to detect contrast sensitivity and global dot motion.
What are the mechanisms of training-induced visual recovery following V1 damage?
- Training can induce plasticity in spared cortex next to lesion.
- Training strengthens neural pathways that bypass V1 and project to extrastriate cortex.
- Training recruits or inhibits visual areas in the intact hemisphere.
How can visual discrimination training recover visual functions in cortically blind fields?
Barbot et al., (2021) tested this performance on 2 chronically CB patients, and found both recovered performance on the tasks consistent with corresponding location in the intact hemifield.
Can training both inhibit or recruit visual areas in the intact brain hemisphere (IBH)?
Henriksson et al., (2007) found some evidence that visual areas in IBH have a role in residual and trained vision in blind field. Case study on 61 yr old woman with homonymous hemianopia (stroke-induced). Both fMRI and MEG are used to study visual spatial information signals.
