task 1 Flashcards
How to measure consciousness?
1) reporting
2) active maintenance of mental representations
3) strategical processing ( e.g. imagining to play tennis, specific brain areas are involved)
4) spontaneous intentional behavior
Third person data
-brain processes, behavior, environmental interaction etc.
First person data
- conscious experience
- central data for science of consciousness
- can’t be expressed wholly in terms of third-person data
Chalmers: how can we try to find neural correlates of consciousness?
-we need to use the principle of interpretation to determine whether someone is conscious of something
Chalmers: pre-existing bridging principles
- criteria that must be fulfilled to say that someone is conscious and what they are conscious of
- e.g. principle of verbal report and principle of availability for global control
Chalmers: principle of verbal report
-when something is reported it is conscious
Chalmers: principle of availability for global control
- if information is available for response in many motor modalities -> it is conscious
(e. g. talk about it, point in direction, press bar)
Using bridging principles to produce rational reconstruction
- we do not measure consciousness directly
- we detect the functional property (verbal report)
- > then we correlate it with a specific neural process
Chalmers draws 6 conclusions:
1) NCC is a mechanism that subserves global availability in the brain ( not just a symptom)
2) 2 functions of the neural process associated with consciousness: explains global availability and isolates the process that underlie consciousness itself
3) there will be many NCCs as there are many mechanisms of global availability
4) there is a possibility of a consciousness module: a localizable, internally integrated area through which all global activity runs
5) it is likely that the neural process involved in explaining access consciousness will simultaneously be involved in basis of phenomenal consciousness
6) we cannot definitely establish a given NCC as an independent test for consciousness bc. we do not know if the functional property we started with is the right criterion
Vegetative disorder:
- awake from coma but no signs of awareness
- diagnosis depends on: no reproducible evidence of purposeful behavior in response to external stimulation
- > there may exist preserved brain function which could be used to detect consciousness awareness
Case study: 23 year old, brain injury, woke from coma, sleep-wake cycles, but unresponsive
fMRI study 1:
- measure neural responses to spoken sentences and compare with response to acoustically matched noise sequences
- speech-specific activity observed bilaterally in middle and superior temporal gyro
- sentences containing ambiguous words -> additional significant response reflecting speech comprehension
- > NOT evidence for conscious awareness
Case study: 23 year old, brain injury, woke from coma, sleep-wake cycles, but unresponsive
fMRI study 2:
- gave spoken instructions to perform mental imagery (play tennis & walk through own house)
- significant activity in related brain areas (NCC), same as in healthy volunteers
-> one could argue that this represents a clear act of intention -> it could confirm conscious awareness of herself and surroundings
Criticism case study 23 year old
- shouldn’t generalize from a single patient (with relatively few cerebral lesions) to most other vegetative state patients (with massive structural brain lesions)
- why wouldn’t she be able to engage in intentional motor acts, given there is no functional/structural lesion? -> does not make sense that she is conscious
- can we determine whether a person is conscious only on a basis of a question-brain activation method?
The light is on but is anybody home?
-study: presenting vegetative patients with a familiar voice saying their name
- activation of primary auditory cortex and higher order association areas in temporal lobe
- BUT: does not tell us whether patients were actually aware of hearing their names, nor does it tell us that this processing was consciously willed
- brain is trained all life long, very sensitive to our own name -> could be an automatic unconscious response
study: willful modulation of brain activity and yes/no task
Task 1: imagery task (playing tennis and walking around house)
Task 2: communication (one type of imagery serves as an affirmative, the other as a negative answer
- 4 vegetatives could willfully modulate their brain activity
- 2 of the 4 revealed some sign of awareness at additional bedside testing
- 1 patients could do yes/no task
- brain activity lighted up that normally can’t be linked to yes/no
- thinking ‘yes’ would normally not make motor areas lighten up
- > it was not random
