Perception and disorders

Question 1

What function does area v4 serve?

Answer 1

Colour perception

Question 2

What is the name of the disorder that involves a deficit in colour perception?

Answer 2

Achromatopsia.

Question 3

What do we know about the case of oliver sacks?

Answer 3

• He suffered a brain injury to v4
• Could see everything in finite detail but in black and white
• dreamed in b+w

Question 4

Who introduced findings that colour perception was specific to v4?

Answer 4

Zeki:
1973 - identified cells in v4 that seemed to be especially sensitive to colour
1983 - these cells demonstrate colour constancY

Question 5

What is colour constancy?

Answer 5

A perceptual phenomenon in which a colour seems familiar across many different lighting conditions.

Question 6

As well as Zekis work, what did other studies conclude about colour perception?

Answer 6

As well as v4, colour conditions in studies activated areas on the ventral surface of the occipital lobe
- v4 is the main boy but there are other areas containing cells which are linked to colour perception.

Question 7

What questions do we have about colour perception?

Answer 7

• How/where is colour processed? - this is an active debate

- Controversy over whether human brains (in particular v4) are completely homologous to monkeys.

Question 8

What do you think about the view that the v4 is completely responsible for colour perception?

Answer 8

This is too simplistic. Other areas have been found to contain colour sensitive cells

• eg Bartels and Zeki
• Beauchamp

Question 9

What function does area v5 serve?

Answer 9

Sensitive to movement and direction of movement.

Question 10

What did Martinez-Trujilo et al find specifically about v5?

Answer 10

From fMRI scans - there are cells in v5 which are selective to SPEED OF MOTION.

Question 11

What name is given to the disorder in which the person has a deficit in perception of motion?

Answer 11

Akinetopsia.

- viewing the world as ‘a series of snapshots’.

Question 12

What finding did MRI and PET scans reveal about activation in other areas of the brain in instances where there was damage to v5?

Answer 12

There was little/no activation in the intact areas v1 and v2 - this is different to healthy participants.

Question 13

Beckers and Zeki (1995) conducted which type of study to examine v5 damage?

Answer 13

TMS studies - temporary lesions.

Question 14

What deficit appears when damage is in v1?

Answer 14

Cortical blindness

Question 15

Which types of blindness are there?

Answer 15

• Complete v1 damage = blindness
• hemianopia - a lesion in one hemisphere
• scotoma - a smaller lesion
• blindsight

Question 16

What is blindsight?

Answer 16

A phenomenon where individuals that are cortically blind in a part of their visual field demonstrate unconscious visual processing of stimuli in that visual field.

Question 17

What is the case of patient D.B?

Answer 17

• He had hemianopia - a lesion in his right hemisphere (no vision in his left field).
• He acted/felt blind
• Weiskrantz (1986) - found that despite his deficit he could locate stimuli but had no conscious effort of doing so.

Question 18

What explanations can we provide for blindsight occuring?

Answer 18

• residual neural activity in v1?
• fast connection to v5?
• processing in the retinogeniculate pathway - is it direct to othere visual areas?

Question 19

What can be said about explanations for blindsight? (evaluate them)

Answer 19

• Residual v1 neural activity - NO. Blindsight is still evident in patients whose entire v1 has been removed (Tovee, 2008).
• fast connections to v5 - little support from studies of monkeys BUT evidence that the v5 may become active before or simultaneously with v1 (Ffythche et al, 1995)/

Question 20

What explanation do Danckert and Goodale (2000) provide for blindsight?

Answer 20

It may be due to the normal functioning of secondary pathways - these are outside of conscious perception.

Question 21

What other perceptive deficits are there?

Answer 21

• depth perception
• recognition of faces
• recognition of objects
• visually guided action

Question 22

What are the names of the 2 distinct pathways from the V1 onwards?

Answer 22

• Dorsal stream

- Ventral stream

Question 23

What are the characteristics of the dorsal stream?

Answer 23

• the WHERE pathway
• projects to the posterior parietal cortex (PPC)
• perceiving where an object is.

Question 24

What are the characteristics of the ventral stream?

Answer 24

• the WHAT pathway
• projects to the inferior temporal cortex (IT)
• perceiving what an object is