Week 12 Clinical Neuropsychology

Question 1

What 2 things would happen if you had localised damage to V1?

Answer 1

Would give you scotomas / blind spots

1. Orientation would be impaired
2. Local motion pooling impaired
   - Inability to extract specific elements of stimuli and pass onto more complex processing in the visual processing system, V2, V3, V4, V5

Question 2

What would happen if you had total damage to V1?

Answer 2

Completely blind = total damage

Question 3

What is blindsight and how is some sight still retained?

Answer 3

A crude ability to see and resolve objects, with very poor spatial acuity with no conscious awareness to see objects

Blindsight occurs from the limited functioning of V1 and magnocellular shortcut processing which may still be retained, or have pockets of visual perception in a mostly damaged V1

Question 4

How is blindsight tested?

Answer 4

Flash stimuli left or to the right of a fixation point
Tell us when you think its on the left or the right, 80% above chance levels in forced choice paradigms

Question 5

How to tap V1 and V5 using TMS stimulation?

Answer 5

Stimulate the brain region + cognitive task!

1. Stimulation to V1 50 ms after stimuli was presented - motion processing was impaired, shows that it takes 50ms for stimulus to get from eyes to V1
2. Stimulation to v5: after 70 ms after stimuli motion processing was impaired, showing that it takes 70 ms for stimulus to get to V1 to V5
3. 90ms taken for reentrant processing from V5 back to V1

Question 6

How is visual agnosia caused and in what pathway?

Answer 6

1. It is caused by strokes or carbon monoxide poisoning)
2. Mostly likely in the occipital lobe and/or early in ventral pathway - inability to visually recognise an object but not impaired to other senses

Inability to pool V1 to form global configurations of stimuli

Question 7

The type of damage to the ventral pathway influence the type of visual agnosia caused - what are 3 different types?

Answer 7

1. Early damage in pathway = affects object perception
2. Late damage in pathway = object recognition
3. Specific damage = prosopagnosia (face blindness)

Question 8

What is the main limitation of traditional studies on prosopagnosia?

Answer 8

Problem with early prosopagnosia face blindness studies is that they were comparing facial recognition with stimuli that weren’t categorically similar, such s tables and chairs.

As most tables and chairs are usually completely different in size and shape and do not belong to the same specific category, it is not an effective comparison to make with faces, which have very similar features.

An improved study would be to compare faces with other similar looking stimuli of the same category, or do multiple trials over time.

Question 9

What types of stimuli show the inversion effect?

Answer 9

Highly familiar objects, most primarily faces, have the inversion effect = features in isolation, but spatial global information is impaired, indicates second order effects of stimuli

Question 10

What are the two stages of visual processing? Lissauer in 1890

Answer 10

1. Formation of the percept - visual pooling of information
2. Retrieving stored memories of the percept (semantic processing)

Question 11

What are the two different types of visual agnosia?

Answer 11

1. Apperceptive agnosia = effects ability to form percepts of objects due to damage early in the pathway
2. Associative agnosia = impaired recognition and retrieval of memory of percept due to damage later in the ventral pathway

Question 12

What will people with apperceptive and associative agnosia see and perceive?

Answer 12

They would see isolated features, but not be able to perceive a global configuration of an object

Associative agnosia - the man who thought a hat was his wife’s head, see the percept, unable to recognise it

Question 13

Why does apperceptive agnosia occur after early ventral damage?

Answer 13

This is because if damage occurs early in pathway, ability to integrate V1 cells to form a coherent percept will be impaired - Grouping of contours of objects and segmentation of other objects figure ground segmentation is impaired

Question 14

What type of visual agnosia did HJA have and what were their qualities?

Answer 14

Case study: H.J.A - damage to ventral pathway, apperceptive agnosia
Damage to occipital temporal region

1. Damage to Face, object, word and colour perception
2. Other tactile senses used to recognise objects as other senses were not impaired
3. She had naming and semantic understanding of objects
4. Shape discrimination and orientation was fine
5. Could do parallel visual task from Treisman distractor task (all local features, no global configuration)

Question 15

Why would it be incorrect to say that people with apperceptive agnosia has a tendency to oversegment/break down the visual scene into smaller pieces?

Answer 15

because they never could form an entire percept in the first place - they are only able to perceive local features of a stimulus

Question 16

What would V4 damage cause?

Answer 16

1. inability to do colour processing - achromatopsia, either form or hue processing, ie. a in the Farnswell Manswell test, damage to parvo blob) or using colour to extract form information (Ishihara, damage to parvo interblob)

Question 17

What are three conditions that result after dorsal damage?

Answer 17

Balents syndrome - 3 pathologies
1. Simultagnosia - fragmented representation of spatial motion
Focus attention on small part of visual scene and unable to process global scene

2. Optic ataxia - difficulty in pointing to a visual defined object
   Ocular apraxia - inability to shift gaze to a new target
   Dyslexia is common after posterior-parietal damage

Question 18

What did LM suffer from and where was the damage?

Answer 18

She had cortical blood-flow blockage which damaged the V5/MT in dorsal stream
- objects appeared to be restless and jumping around!

Question 19

Why was LM better at writing with her eyes closed than eyes open?

Answer 19

Avoiding cue conflict! She was probably better in the eyes-closed condition with writing because her impaired frozen like perception of motion wouldn’t interfere with her other senses needed for writing, ie. touch and spatial orientation.

She probably relied on proprioception to tell her where her hand was as she was writing, which could be less distracting and dizzying than her fragmented vision.

Question 20

Why can’t LM be motion blind?

Answer 20

There are multiple pathways involved in motion processing that start from complex cells in V1 to the dorsal pathways in higher processing stages such as V5, involved in motion pooling. To be completely motion blind would be to have an impaired V1 which would implicate other types of vision processing.

Question 21

What tasks could LM probably do?

Answer 21

When the motion signal is coherent, (global motion paradigms) she can extract motion effectively, but cannot do signal-to-noise processing which occurs in V5 and tactile (non-visual) motion.

She could do complex motion pooling in the dorsal pathway from form processing but couldn’t determine the direction of motion (V5).

Question 22

How to assist people with apperceptive agnosia?

How to assist people with associative agnosia?

Answer 22

1. Apperceptive agnosia - object percept

If you rotate an object, you could use the kinetic depth effect, to use motion signals to do form processing to discriminate an object.

2. Associate agnosia - object recognition

Get them to use other sensory modalities such as touch, taste, smell to distinguish the object, allow them to form other associations outside of the visual system to define objects.

Question 23

Why is it inaccurate to say that the dorsal pathway has no role on visual processing?

Answer 23

Motion cannot be separated from visual perception as motion processing is part of a stage within the visual processing system

Motion encompasses both motor activities performed by the self and also the extraction of surrounding motion from our environment

What is more accurate to say is that the dorsal pathway may be more mediated in motor representation since it’s closer to the motor cortex.

Question 24

Is there a 3rd pathway? / crosstalk

Answer 24

There is good evidence that we have a third pathway for form processing for social information or another parallel pathway within the ventral stream.

While LM shows demarcation between dorsal and ventral, normal people can distinguish motion signals of form and motion due to crosstalk between dorsal and ventral.