2. Illusions and lesions

Question 1

What does it mean that conscious perception is construction of the senses?

Answer 1

It is not exact replica of outside world! 1/3 of the time we are blind as incoming information is restricted to point of fixation

Question 2

What are examples of conscious perception being construction of the senses?

Answer 2

1) Array of pink dots disappearing (brain gets bored with unchanging stimuli).
2) Necker cube (only one interpretation at the time).
3) The “dress” argument (same light wavelength, but different assumptions).
4) Chess board
5) Ebbinghaus illusion

Question 3

anterior

Answer 3

in front, toward the face

Question 4

posterior

Answer 4

behind, toward the back

Question 5

superior

Answer 5

above, toward the head

Question 6

inferior

Answer 6

below, toward the feet

Question 7

medial

Answer 7

toward the middle

Question 8

lateral

Answer 8

toward the edge

Question 9

dorsal

Answer 9

toward the top of the brain or the back of the spinal cord

Question 10

ventral

Answer 10

toward the bottom of the brain or the front of the spinal cord

Question 11

saggital

Answer 11

divides into right and left part

Question 12

coronal

Answer 12

divides into front (anterior) and back (posterior)

Question 13

axial

Answer 13

divides into dorsal and ventral plane

Question 14

traumatic brain injury

Answer 14

intracranial injury - injury to brain caused by external force (accidents)

Question 15

stroke

Answer 15

when blood vessels are clogged, blood cannot pass, regions don’t get the oxygen and die

Question 16

ischemic stroke

Answer 16

blockage of blood vessel, lack of blood flow to affected area

Question 17

hemorrhagic stroke

Answer 17

rupture of blood vessel, leakage of blood

Question 18

tumour

Answer 18

abnormal cells

Question 19

blinsight - symptoms

Answer 19

cortical blindness - patients claim to NOT see anything in affected field
however, if they are forced to choose what they saw, their responses are above chance
also some brain lesions may lead to disorders of attention/awareness

Question 20

blindsight - areas affected

Answer 20

occipital lobe, at least V1 affected, effects of damage map contralaterally to the affected visual field, both gray and white matter affected

Question 21

What can blinsight patients under forced-choice guessing do?

Answer 21

discriminate shapes, colour and orientation
reach for object
accurately position hand for grasping
motion perception

Question 22

Why blindisight patients can perform force-choice task?

Answer 22

Most of visual information (90%) travels to V1 (which is affected in blindsight).
However, the 10% goes to dorsal stream and superior colliculus. Those regions may be responsible for being able to perform forced-choice task.

Question 23

Why should we sceptical about studies with blindsight patients?

Answer 23

Blinsight in monkeys -> monkeys have great sound perception (potential confound)

Human patients -> you need to trust patients that they truly don’t see anything (however, in practice, many of those patients are participating in many experiments -> pressure to respond according to their previous performance)

Question 24

hemispatal neglect - area affected

Answer 24

(right) parietal damage

Question 25

hemispatial neglect - symptoms

Answer 25

after damage to one brain hemisphere, deficit in attention to and awareness of one side of space is observed
attention seems to be affected - pre-occupied with only one side of the visual field

Question 26

hemispatial neglect - typical findings

Answer 26

1) drawing half of objects (both in case of copying and spontaneous drawing)
2) disecting the line moved to the side
3) eye-movements ‘‘heatmaps’’ reveal bias towards one hemifield
4) curious finding! upon seeing two houses (one of them on fire - usually the one on the left), patients claim that houses look the same, but they would prefer to live in the house on the right

Question 27

How does hemispatial neglect support Global Workspace Theory?

Answer 27

attention is nevessary for consciousness

Question 28

Visual form agnosia

Answer 28

In case of DF it arised due to CO poisoning and damage to LOC (lateral occipital cortex).

Question 29

What is specific to LOC?

Answer 29

It likes objects (higher activity when seeing real objects vs scrambled ones)

Question 30

visual form agnosia - DF case

Answer 30

1) cannot copy objects, but can draw them from memory (DF-SPECIFIC finding)
2) she is unable to identify shape of objects
3) she knows what the objects are (+is able to recognize them by color)

Question 31

What are main findings from slot task for DF?

Answer 31

She struggles with matching (saying how is the thing oriented and matching it).
However, she is good at posting! So even though she is unaware of information, she can use it

Question 32

What can DF slot task performance inform us about unconscious behaviour?

Answer 32

There seems to be dissociation between perception and action. It may be linked to the fact that ventral stream (affected in DF case) related to problems in perception (matching) but not so much by action

Question 33

dorsal attention system

Answer 33

top-down attention (FEF - frontal eye fields + IPS - intraparietal sulcus), voluntary attention

Question 34

ventral attention system

Answer 34

bottom-up attention (TPJ - temporo parietal junction + VFC - ventral frontal cortex); detection in enviornmentally salient stimuli

Question 35

What similarities are there between DF slot performance and healthy humans?

Answer 35

Perception suffers from illusions, but action is not influenced by illusions.

Healthy subjects participated in Ebbinghaus illusion in which the central disks were either:
perceptually different + physically identical;
or
perceptually identical + physically different

The grip sizes were NOT FOOLED by the illusion.

Question 36

What can we conclude on the basis of those findings?

Answer 36

Ventral stream -> related to consciousness
Dorsal stream -> related to action which is automatic (unconscious)
However, this idea is simplification! There is crosstalk between streams, so there is just relative difference between processing routes!

Question 37

What are other ventral stream deficits?

Answer 37

• color agnosia (V4 damage)
• prosopagnosia (face blindenss)
• motion blindness (MT/V5 damage)

Question 38

apperceptive agnosia

Answer 38

difficulty in assembling the pieces together into meaningful whole

Question 39

associative agnosia

Answer 39

object perception intact, but there is issue in assigning meaning or identity to it