Affective Blindsight Flashcards
What are the first steps of visual processing?
- Vision begins in the retina, starting as dots and becoming more complex as it travels back in the brain to the striate cortex
- It is then interpreted into meaningful pictures as signals travel forward to the associative
Areas
What does damage to different areas of the vision system cause?
Different types of blindness
How is the visual field represented retinotopically in the first cortical region?
inverted both along the top down and left right axes (swaps sides)
If a patient damages upper left side of visual area of brain, where would they see a blind spot in their vision?
Lower right side
What does bilateral damage to visual cortex cause?
Double hemianopia - complete blindness
Why would a person have no damage to optic nervous system, eyes or retina but experience blindness?
Lesions to the cortical region
What are the 4 signs of cortical blindness or hemianopia?
- No blink response to threat
- Opto-kinetic reflex may be absent
- No alpha rhythm on posterior region (no open/closing of eyes)
- Photic reflex often persists
What is Anton’s syndrome?
Denial of blindness (anosognosia)
Associated with cortical blindness
With cortical blindness, (posterior lesions)) what other area may be affected?
If the lesions are large, the 2 hippocampus might be affected
Possible amnesia also
In what 4 steps can recovery from cortical blindness occur?
- Presence/absence of light
- Primitive movement
- Contours
- Colours
Helen the monkey had lesions and cortical blindness but was still able to do what?
Navigate her way around obstacles
Patient DB had an operation in the right occipital area and presents left hemianopia which develops into an inferior left quadrantopia. What is3 things is DB able to do?
- Orient his gaze towards stimulus in his blind field
- Locate and point to stimulus
- Can tell if stimulus is horizontal or vertical
When tested patient DB who had cortical blindness and said he could not see anything could actually detect above chance what?
X or O
The presence of movement
Geometric shapes
Colours
Direction of movement
Spatial frequency
Flicker
When there is no striate cortex (cortical blindness) what is the alternative system proposed by Weiskrantz to explain why images can be detected?
The input to the superior colliculus is processing the information
10% of fibres project to the superior colliculus
What is the geniculo-striate pathway to sight?
Retina-LGN-V1-V2-temporal and parietal regions
What is the retina-tectal pathway to sight?
Retina-superior colliculus-pulvinar-temporal and parietal regions
What are 2 hypotheses for blindsight?
- The superior colliculus is responsible for sight
2. Geniculo-extrastriate pathways
What is the evidence for the hypothesis that the superior colliculus is responsible for blindsight? (3)
- Colliculus is 2nd sight system more used in monkeys than humans
- In monkeys destruction of superior colliculus makes blindsight disappear
- In humans a distractor in blind field slows saccades towards targets in sighted field
Patient TN had cortical blindness but what was found when tested with shapes and faces?
He could detect shapes at chance
Faces vs non faces at chance
Above chance when detecting emotions on faces
When testing affective blindsight by showing participants a range of emotional faces in an fMRI, what area of the brain was found to be active?
The amygdala even though no visual cortex to process and said they couldn’t see anything
What is affective blindsight?
Sight for emotional faces although can’t see (cortical blindness )
What is the path Ledoux suggests for rapid, subcortical pathway for stimuli representing threat? (Not necessary for consciousness)
High road- Emotional stimulus- sensory thalamus -sensory cortex-amygdala-emotional response
Low road- emotional stimulus-amygdala- emotional response
Low road not necessary for consciousness- bypass sensory cortex - process threat fast
Why would people with cortical blindness be still able to process emotional faces?
Low road of emotional stimuli
Emotional stimulus- sensory thalamus- amygdala emotional response
Helps process threat fast by bypassing the sensory cortex
If keeping with Weiskrantz’s model for blindsight, how can affective blindsight work?
Retina - superior colliculus - pulvinar - amygdala
What did Morris et al do to find proof of Ledoux’s retino-tectal pathway for affective blindsight? Methods results conclusions
Methods: combined conditioned angry faces pictures with a white noise and just the angry face picture in unconditioned while in fMRI
Presented super fast so undetectable
Results: conditioned faces (with noise) activated the right amygdala
For conditioned , non seen faces, activity found in superior colliculus and pulvinar which correlates with activity in the amygdala
Conclusions: even when presented too fast to detect, still response from amygdala
What was found about the speed of processing in affective blindsight with EEG testing with patient TN?
TN shown angry and neutral faces with EEG differences shown in oscillatory activity for fee and happiness
Brain responds very rapidly
What type of spatial frequency is responsible for sub cortical pathways to detect stimulus features in affective blindsight?
Low spatial frequency which conveys crude information
Amygdala doesn’t respond to what type of frequency?
High spatial frequency which conveys details
What was found in patient TN in a block design paradigm, fearful and neutral faces, either filtered or non filtered for high or low frequency?
Amygdala response was greatest for fear than neutral for unfiltered (broadband) and low spatial frequencies
Concluded that sub cortical pathway only uses crude low frequency information
What was the ‘gaze blindsight ‘ experiment conducted with TN? Methods results conclusions
Methods: presented TN with simulation faces starting directly at him or away from him
Results: he was able to just above chance tell if the face was looking at him.
Direct gaze also stimulates amygdala
Conclusions: relevant stimulus blindsight. In the absence of sight amygdala processes relevant stimulus
