disorders of visual perception Flashcards
Describe the key characteristics of a number of disorders of visual perception (neglect, blindsight & prosopagnosia)
-Neglect, specifically hemispatial neglect, is a disorder of attention and awareness where an individual fails to notice anything on one side of their visual field, typically the left. This condition often follows damage to the right hemisphere of the brain, such as after a stroke. It’s not that the person is blind to the ignored half; rather, they do not attend to it. If you draw a clock, they might only put numbers 12 through 6, ignoring the left side. It’s as if that part of the world ceases to exist for them, not due to a lack of vision but because of a deficit in attention and awareness.
Key Characteristics:
Ignoring objects, sounds, and even their own body parts on one side of space (usually the left).
Difficulty in engaging with the neglected side, even when reminded.
Often unaware of their deficit.
-Blindsight is a fascinating condition where individuals who are blind in a certain area of their visual field, due to damage to the primary visual cortex, can still respond to visual stimuli without consciously seeing them. For example, they might catch a ball coming from the blind spot or navigate around obstacles without conscious awareness of them. This suggests that some aspects of visual processing occur outside of conscious perception, likely involving alternative brain pathways that bypass the primary visual cortex.
Key Characteristics:
Ability to detect or respond to visual stimuli without conscious perception.
Occurs in people with damage to the primary visual cortex.
Demonstrates the complexity of visual processing pathways in the brain.
-Prosopagnosia is a disorder characterized by the inability to recognize faces, including one’s own reflection in severe cases. People with prosopagnosia can see faces and often describe them in detail but fail to recognize the face’s identity. This condition can be congenital (present from birth) or acquired due to brain injury, particularly to the fusiform gyrus, a region involved in face perception. Those with prosopagnosia might use alternative strategies to recognize individuals, such as relying on voice, clothing, or unique physical characteristics.
Key Characteristics:
Difficulty or inability to recognize familiar faces, sometimes even their own.
Normal vision and intellectual functioning, with specific deficits in face perception.
Relying on non-facial cues for personal identification.
How do these disorders relate to and help to understand normal visual perception?
The study of disorders such as neglect, blindsight, and prosopagnosia offers profound insights into the normal mechanisms of visual perception by highlighting the brain’s complexity and the specialized regions of its different fucntions. Through understanding these disorders, we can appreciate the processes underlying our ability to see, process to, and interpret the visual world.
Neglect and Spatial Awareness
Neglect demonstrates the brain’s role in spatial awareness and attention. In individuals with neglect, the ability to attend to one side of space is impaired, not because of a lack of vision but because of a deficit in awareness and attention processing. This condition underscores the distinction between seeing and consciously processing to what we see. It highlights the brain’s role in integrating visual information with spatial awareness and attention, for normal visual perception.
Blindsight and Visual Processing Pathways
Blindsight reveals that visual perception involves multiple processing pathways beyond the primary visual cortex, where individuals can respond to visual stimuli without conscious perception suggests the existence of alternate visual pathways that bypass the primary visual cortex
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Prosopagnosia and Face Recognition
Prosopagnosia, provides an insight into how the brain processes faces differently from other objects. The inability of individuals with prosopagnosia to recognize faces, despite being able to see and describe them, points to specialized neural mechanisms dedicated to face perception. This disorder has led to the identification of the fusiform face area (FFA) in the brain, a region specifically involved in recognising faces.
Critically consider explanations for these disorders
Neglect –> Critical Consideration: While the association between right parietal lobe damage and neglect is well-established, neglect presents a complexity that cannot be fully explained by damage to a single brain region. The occurrence of neglect following lesions in different brain areas suggests a distributed network responsible for spatial attention and awareness. This indicates that neglect results from the disruption of multiple regions rather than the failure of a single region.
Critical Consideration: The explanation for blindsight challenges the traditional view of a hierarchical visual system where the primary visual cortex is essential for visual perception. It highlights the role of alternate pathways, possibly through the brainstem or midbrain structures like the superior colliculus, which project to secondary visual areas.
Critical Consideration: While damage to the FFA is a common explanation for prosopagnosia, the disorder can also occur in individuals without any apparent brain damage, indicating a more complex aetiology. Furthermore, research suggests that other regions, including the occipital face area and the anterior temporal lobe, also play roles in face recognition. This suggested that different regions are appointed for face processing, and disruption in any part of these can lead to prosopagnosia.
