Perception and disorders Flashcards
What function does area v4 serve?
Colour perception
What is the name of the disorder that involves a deficit in colour perception?
Achromatopsia.
What do we know about the case of oliver sacks?
- He suffered a brain injury to v4
- Could see everything in finite detail but in black and white
- dreamed in b+w
Who introduced findings that colour perception was specific to v4?
Zeki:
1973 - identified cells in v4 that seemed to be especially sensitive to colour
1983 - these cells demonstrate colour constancY
What is colour constancy?
A perceptual phenomenon in which a colour seems familiar across many different lighting conditions.
As well as Zekis work, what did other studies conclude about colour perception?
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.
What questions do we have about colour perception?
- How/where is colour processed? - this is an active debate
- Controversy over whether human brains (in particular v4) are completely homologous to monkeys.
What do you think about the view that the v4 is completely responsible for colour perception?
This is too simplistic. Other areas have been found to contain colour sensitive cells
- eg Bartels and Zeki
- Beauchamp
What function does area v5 serve?
Sensitive to movement and direction of movement.
What did Martinez-Trujilo et al find specifically about v5?
From fMRI scans - there are cells in v5 which are selective to SPEED OF MOTION.
What name is given to the disorder in which the person has a deficit in perception of motion?
Akinetopsia.
- viewing the world as ‘a series of snapshots’.
What finding did MRI and PET scans reveal about activation in other areas of the brain in instances where there was damage to v5?
There was little/no activation in the intact areas v1 and v2 - this is different to healthy participants.
Beckers and Zeki (1995) conducted which type of study to examine v5 damage?
TMS studies - temporary lesions.
What deficit appears when damage is in v1?
Cortical blindness
Which types of blindness are there?
- Complete v1 damage = blindness
- hemianopia - a lesion in one hemisphere
- scotoma - a smaller lesion
- blindsight
What is blindsight?
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.
What is the case of patient D.B?
- 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.
What explanations can we provide for blindsight occuring?
- residual neural activity in v1?
- fast connection to v5?
- processing in the retinogeniculate pathway - is it direct to othere visual areas?
What can be said about explanations for blindsight? (evaluate them)
- 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)/
What explanation do Danckert and Goodale (2000) provide for blindsight?
It may be due to the normal functioning of secondary pathways - these are outside of conscious perception.
What other perceptive deficits are there?
- depth perception
- recognition of faces
- recognition of objects
- visually guided action
What are the names of the 2 distinct pathways from the V1 onwards?
- Dorsal stream
- Ventral stream
What are the characteristics of the dorsal stream?
- the WHERE pathway
- projects to the posterior parietal cortex (PPC)
- perceiving where an object is.
What are the characteristics of the ventral stream?
- the WHAT pathway
- projects to the inferior temporal cortex (IT)
- perceiving what an object is
