Perceptual Dysfunction

Question 1

Sensation

What is Perception?

Answer 1

• the detection of internal or external stimulation.
• Raw information about the environment is made available to the brain through the senses.

Question 2

Perception

What is Perception?

Answer 2

• the awareness and interpretation of sensory information by the brain (YOUR subjective experience)
• Perceptual deficits can occur without sensory impairment

Question 3

First part of the cortex to receive visual information

Answer 3

Visual information travels from the retina, through subcortical areas, to V1: Primary Visual Cortex

Question 4

V1 Damage

Answer 4

• 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

Question 5

The existence of blindsight can tell us about…

Answer 5

…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.

Question 6

Bilateral damage to secondary cortex V5

Answer 6

(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

Question 7

Higher Visual Cortices II - Visual Association Cortices

Answer 7

Receive input from visual cortex and from the cortices of one or more sensory systems for multisensory integration

Question 8

Higher Visual Cortices II - Dorsal Stream

Answer 8

Flows from V1 to dorsal prestriate cortex to posterior parietal association cortex

Question 9

Higher Visual Cortices II - Ventral Stream

Answer 9

Flows from V1 to ventral prestriate cortex to the inferotemporal

Question 10

What are the functions of the two streams (dorsal and ventral)? THEORIES

Answer 10

• Theory 1: “What vs Where”
• Theory 2: “Action vs Perception”

Question 11

Theory 1: “What vs Where”

What are the functions of the two streams (dorsal and ventral)? THEORIES

Answer 11

One stream processed “where” information, and one stream processed “what” information

Question 12

Theory 1: “What vs Where” - Monkeys with different lesions

What are the functions of the two streams (dorsal and ventral)? THEORIES

Answer 12

• 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)

Question 13

Theory 1: “What vs Where” - support in human patients

What are the functions of the two streams (dorsal and ventral)? THEORIES

Answer 13

• 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

Question 14

Theory 2: “Action vs Perception” - PATIENT DF

What are the functions of the two streams (dorsal and ventral)? THEORIES

Answer 14

• 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

Question 15

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

Answer 15

• …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)

Question 16

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

Answer 16

• 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)

Question 17

Ventral stream damage Agnosias

Answer 17

• 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

Question 18

Damage to the ventral visual pathway leads to visual agnosias, including:

Answer 18

• Apperceptive agnosia
• Associative agnosia

Question 19

Apperceptive agnosia

Damage to the ventral visual pathway leads to visual agnosias, including:

Answer 19

• …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

Question 20

Associative agnosia

Damage to the ventral visual pathway leads to visual agnosias, including:

Answer 20

• 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.

Question 21

Prosopagnosia

Answer 21

• 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)

Question 22

Prosopagnosia Treatment

Answer 22

• Training programmes are being investigated, with mixed results
• Patients may develop coping strategies (e.g., attending to other features, seating students in particular locations…)

Question 23

Face processing involves a
network of occipito-temporal
areas including:

Face Perception

Answer 23

• Fusiform face area (FFA)
• Occipital face area (OFA)
• Anterior temporal cortex (AT)

Question 24

Prosopagnosics often have
WHAT type of damage?

Answer 24

Bilateral