Perceptual Dysfunction Flashcards
Sensation
What is Perception?
- the detection of internal or external stimulation.
- Raw information about the environment is made available to the brain through the senses.
Perception
What is Perception?
- the awareness and interpretation of sensory information by the brain (YOUR subjective experience)
- Perceptual deficits can occur without sensory impairment
First part of the cortex to receive visual information
Visual information travels from the retina, through subcortical areas, to V1: Primary Visual Cortex
V1 Damage
- Patients with large lesions to the primary visual cortex occasionally retain some visual abilities: blindsight
- But most of the time, can report that they can’t see, even when their eyes are working
The existence of blindsight can tell us about…
…about more visual pathways in the brain, other than the primary V1:
- Higher Visual Cortices I:
- Secondary visual cortices (~24): Receive much of their input from V1
- Process visual information with regard to form, motion, shape, etc.
Bilateral damage to secondary cortex V5
(secondary visual) = selective loss of visual motion perception
- Can determine that things are there, but not able to describe them/process them unlike one usually would
- Akinetopsia
Higher Visual Cortices II - Visual Association Cortices
Receive input from visual cortex and from the cortices of one or more sensory systems for multisensory integration
Higher Visual Cortices II - Dorsal Stream
Flows from V1 to dorsal prestriate cortex to posterior parietal association cortex
Higher Visual Cortices II - Ventral Stream
Flows from V1 to ventral prestriate cortex to the inferotemporal
What are the functions of the two streams (dorsal and ventral)? THEORIES
- Theory 1: “What vs Where”
- Theory 2: “Action vs Perception”
Theory 1: “What vs Where”
What are the functions of the two streams (dorsal and ventral)? THEORIES
One stream processed “where” information, and one stream processed “what” information
Theory 1: “What vs Where” - Monkeys with different lesions
What are the functions of the two streams (dorsal and ventral)? THEORIES
- Monkeys with lesions to inferotemporal cortex: impaired at discriminating objects = VENTRAL STREAM (WHAT PATHWAY)
- Monkeys with lesions to the posterior parietal cortex fail to perform on location tasks = DORSAL (WHERE PATHWAY)
Theory 1: “What vs Where” - support in human patients
What are the functions of the two streams (dorsal and ventral)? THEORIES
- Patients with damage to inferotemporal cortex (part of the “what” pathway) often have no difficulty reaching for objects that they have difficulty describing
- Patients with damage to posterior parietal association cortex (part of the “where” pathway) often have difficulty reaching accurately for objects that they have no difficulty describing
Theory 2: “Action vs Perception” - PATIENT DF
What are the functions of the two streams (dorsal and ventral)? THEORIES
- CHALLENGE: is the card at the same orientation as the slot?. DF had a profound visual form agnosia, but spared visuomotor function. She doesn’t seem to know what the object is, but she knows how to act with it
- WHAT = ventral pathway
- CHALLENGE: grabbing different sized blocks - could not discriminate between them, but accurately changed the width and orientation of her grasp as she reached
Theory 2: “Action vs Perception” - Goodale and Milner argued that the key difference between dorsal and ventral streams is…
What are the functions of the two streams (dorsal and ventral)? THEORIES
- …not the kinds of information (i.e. “what/where”, they carry, but the use to which that information is put
- Dorsal stream: direct behavioural interaction with objects (action)
- Ventral stream: mediate conscious perception of objects (perception)
Theory 2: “Action vs Perception” - What does DF have? What would the opposite patient have?
What are the functions of the two streams (dorsal and ventral)? THEORIES
- DF has a perceptual deficit with spared action
- According to Theory 2, the “opposite patient” to DF would have damage where? Leading to what impairment?
- Damage to the dorsal (action) stream
- Optic ataxia: disorder of visually guided reaching (recall Balint syndrome)
Ventral stream damage Agnosias
- A-gnosia = absence of knowledge (from previous lectures)
- Loss of ability to recognize objects or shapes, etc. (with no evidence of significant memory loss)
- Perceptual, not sensory, deficits
- e.g., blindness due to retinal damage is a sensory visual problem while apperceptive agnosia is a perceptual visual problem
Damage to the ventral visual pathway leads to visual agnosias, including:
- Apperceptive agnosia
- Associative agnosia
Apperceptive agnosia
Damage to the ventral visual pathway leads to visual agnosias, including:
- …failure in object recognition linked to problems in perceptual processing
- EX: No impairment in matching different “normal” views of objects, only “unusual views”
- Ability to recognize degraded stimuli is impaired
Associative agnosia
Damage to the ventral visual pathway leads to visual agnosias, including:
- Normal visual perception but unable to use visual information to recognise things
- Intact performance on perceptual tests, but cannot access names or other information about objects presented visually
- Associative agnosics can copy objects accurately but they can’t tell you what those objects are
- When given names of objects, they can often give accurate verbal descriptions. Underlying representation of the object/category is intact.
Prosopagnosia
- Failure of face recognition with intact object recognition
- Can describe the characteristics of a face without recognition
- Affects previously familiar faces (retrograde) as well as newly experienced faces (anterograde)
- Can still recognize people by their voice, clothing, hair, etc.
- Selective visual deficit; usually occurs in the absence of any other visual impairment, cognitive deficit, or psychiatric illness
- Can be acquired after injury or developmental (present from birth)
Prosopagnosia Treatment
- Training programmes are being investigated, with mixed results
- Patients may develop coping strategies (e.g., attending to other features, seating students in particular locations…)
Face processing involves a
network of occipito-temporal
areas including:
Face Perception
- Fusiform face area (FFA)
- Occipital face area (OFA)
- Anterior temporal cortex (AT)
Prosopagnosics often have
WHAT type of damage?
Bilateral
