Questions and Answers
What is the main difference between the 'what' and 'where' systems in the cortex?
The 'what' system is responsible for processing object features, while the 'where' system is responsible for processing spatial information.
What is the term for the phenomenon where a person is able to respond to visual stimuli without being consciously aware of them?
Blindsight
What is the term for the damage to the primary visual cortex that results in blindness for a corresponding part of the visual field?
Cortical blindness
What is the term for the pathway that is responsible for guiding actions in response to visual stimuli?
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What is the term for the process of encoding relationships between objects in the environment?
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What is the name of the theory that proposes that there are separate neural systems supporting different visual functions?
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What is the term used to describe the symptom of impaired conscious awareness of stimuli in one visual field due to a stimulus in the other visual field?
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What is the pathway involved in guiding actions towards objects in the environment?
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What is the term used to describe the ability to respond to visual stimuli in the absence of conscious awareness of those stimuli?
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What is the name of the theory that proposes two separate visual systems, one for perception and one for action?
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What is the term used to describe the inability to consciously perceive objects in the visual field due to damage to the primary visual cortex?
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What is the name of the pathway involved in object recognition and identification?
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Which brain region is preserved in individuals with blindsight, enabling them to locate targets within their blind visual field?
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What is the primary function of the ventral stream in the visual processing pathway?
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In individuals with cortical blindness, what is the primary cause of their inability to consciously perceive visual stimuli?
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What is the primary characteristic of the dorsal stream in the visual processing pathway?
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What is the term for the type of coding used in the ventral stream, where representations are encoded in reference to objects independent of the observer's perspective?
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Which of the following statements about the dorsal stream is true?
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Study Notes
Primary Visual Pathways and Cortico-Cortical Visual Pathways
- Primary visual pathways: from the retina to the primary visual cortex
- Cortical visual pathways: from primary visual cortex to parietal cortex and temporal cortex
What and Where: Dorsal-Ventral Dichotomy
- Dissociation of "what" and "where" systems in the cortex (Ungerleider & Mishkin, 1982)
- Parietal lesions: dorsal system impairment of spatial information processing (e.g., identify location, landmark)
- Temporal lesions: ventral system impairment of feature processing (e.g., identify object, regardless of spatial position)
Blindsight
- Cortical blindness: damage to part of primary visual cortex, resulting in blindness for corresponding part of visual field
- Blindsight (Weiskrantz, 1986): patient unaware of presence of target in blind portion of visual field, but able to locate target within blind portion
- Patient D.B. (2004): neuropsychological patient with stroke damage to right hemisphere, impaired conscious awareness of stimuli in left visual field
- Patient D.B. able to avoid a rod obstacle in left visual field even when unable to consciously see it
What and How Dichotomy
- Alternative hypothesis (Milner & Goodale, 1995): ventral stream ("what" system) for vision for perception, and dorsal stream ("how" system) for vision for action
- Core characteristics of ventral and dorsal processing streams (Schenk & McIntosh, 2010):
- Ventral stream: vision for perception, produces conscious representations, allocentric (object-centred), long-lasting
- Dorsal stream: vision for action, underlines vision-for-action, reflex-like, often not conscious, egocentric (body-centred), short-lasting
Clinical Neuropsychological Evidence
- Visual agnosia: impairment of object recognition
- Optic ataxia: impairment of visually guided action
- Extinction: symptom in which patient unable to consciously see stimulus in one visual field due to presence of stimulus in other visual field
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