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Consciousness can be viewed as our...
subjective awareness of mental events
Functions of consciousness?
- Monitoring mental events
- Control - it allows us to formulate and reach goals
- Current view in evolution of neuroscience - consciousness evolved to direct or control behaviour in adaptive ways
What is conscious access?
process of becoming aware of stimuli
We typically experience many different states of consciousness. List some examples.
- Spontaneous: daydreaming, drowsiness, dreaming
- Physiologically induced: hallucinations, food or oxygen starvation
- Psychologically induced: hypnosis (seems to be a special state of awareness), meditation
fMRI, frontal lesion studies, and late sustained EEG studies all support need for large, connected integrated brain networks to become aware of an event. What brings about the same activity in the brain? What does this tell us about conscious access?
- Same brain network and neural markers have been implicated in executive functions
- Conscious processing thought to be an executive function where we become aware of event in the mind (in working memory)
What is an interesting finding/observation that could point to a generalised cortical network for tasks that place more cognitive demand or includes novel information.
- Hugdahl et al, 2015
- Very common in fMRI - the close overlap in fronto-parietal activations in healthy individuals to tasks that denote very different cognitive processes. We now suggest that this is because the brain utilizes the EMN network (extrinsic mode network) as a generalized response to tasks that exceeds a cognitive demand threshold and/or requires the processing of novel information.
- eg. Verbal working memory (Duncan) and Spatial working memory (Bergen studies); remembering words/non-words (Duncan) and Wisconsis Card Sorting task (Bergen studies)
- A generalised task-related cortical network that is up-regulated whenever task needs allocation of generalised non-specific cognitive resources, independent of specific of task performed.
- Regardless of framework we are using, clear that brain networks for flexible thinking overlap significantly and that there is indeed this widespread frontoparietal network that seems to be activated in these situations.
The central idea behind GW model is that conscious cognitive content is globally available for diverse cognitive processes. This notion of global availability seems to explain what?
explains the association of consciousness with integrative cognitive processes like attention, decision making and action selection
Global availability is necessarily limited to a __ __ of content, GW theory may naturally account for the __ nature of conscious experience. (__, 2007)
- single stream
- Seth, 2007
Dehaene distinguished between different states of activation/depth of processing. A sort of taxonomy. Depends on:
- Bottom-up stimulus strength
- Top-down attention
In Dehaene's taxonomy of different activation states, what is the first state which occupies the top 2 quadrants in the table? Where bottom-up stimulus strength is weak.
What is the 2 states in Dehaene's model where the bottom-up stimulus strength is strong?
In summary, from this lecture, how can we think about conscious access?
- Can be modelled as an aspect of executive functions that
- allow stimuli to enter space of central executive (workspace, the conscious)
- and can then be treated in a flexible manner and integrate the stimuli with evaluative systems, memory and planning.
The terms executive function and cognitive control refer to processes associated with the control of __ and __.
- thought and action
- (eg. metacognition, planning, selective attention (eg. Go/Nogo task), manipulate info in WM, task switching, response inhibition)
What is conscious access affected by?
- mainly affected by frontal lesions (but not exclusively)
- executive functions share common frontoparietal activity pattern
- There is a common nonlinear recruitment of frontoparietal network when stimulus needs to be processed consciously
What does it mean that consciousness is recruited in a non-linear fashion?
- It is not a gradual change from unconscious to conscious. It is either on or off.
- So, the activation of the frontotemporal lobes differ greatly between conscious and preconscious state.
- When the strong bottom-up stimulus is attended to, suddenly, we observe widespread activation in the frontoparietal regions.
- Dehaene showed in visual masking paradigm that consciously seen stimuli activate wide frontoparietal network, compared to unseen stimuli (both in fMRI and EEG).
- ALSO: look at De Cul in the cards to follow. We can see in the masking paradigm it needs to hit a threshold after which it can ignite.
What is another neuroimaging evidence that suggests widespread frontoparietal connections might be a sign of consciousness?
- fMRi of vegetative state patients
- stimulus evoked activity only seen in sensory cortices
What is a good neuroimaging/neural measurement that correlates with conscious perception?
- Long latency ERP components (event related potential) is good correlate of conscious perception
- De Cul etl al (2007)
- Flashed stimulus followed by backward mask (stimulus to reduce visibility of first stimulus) - people fail to perceive flash unless the interval exceeds 50ms.
- Models of conscious access postulate that this threshold is associated with the time needed to establish sustained activity in recurrent cortical loops - although time and regions are heavily debated
- If the activity manages to sustain beyond a certain threshold, an ignition will take place and it will become conscious. That is why it is non-linear recruitment of consciousness.
What is also interesting about this EEG measure from De Cul's study? (from Youtube video)
- We can see 2 types of activity from this.
- In fusiform gyrus, which is on visual pathway, we can see 2 ERP components. One for visual information (in linear fashion), and then the second for conscious perception. We see activation for 33ms flash, even though we don't consciously perceive it.
- In the PFC, however, there is only one spike (at same latency as second spike in fusiform gyrus), and it is non-linear - this reflects the conscious perception of the visual stimuli.
- Sharp differences in early and late activation which reflects subjectivity of consciousness (associated with P300 wave at scalp level)
Describe an interesting study which seems to dissociate executive attention and conscious feeling of mental effort.
- Naccache et al (2005)
- Dissociation between effort and feeling of effort
- Patient with frontal lesions
- Stroop task slower in difficult, incongruent trials (the obvious Stoop effect)
- HOWEVER, when asked which tasks were the hardest, she couldn't judge her mental efforts. To her, both the congruent easy tasks and the incongruent tasks seemed equally easy.
- Feeling of mental effort selectively deficient but other aspects of introspection preserved (error-detection in this case).
Just for interest, who wrote a paper about conflicts and different methods of measuring consciousness?
Seth et al
Just for interest, what are 2 other theories of consciousness apart from the integration theories we've been looking at?
- Wordly discrimination theory: a person shows they are consciously aware of a feature in the world when they can discriminate it with choice behaviour
- Higher-order thought theory: mental state is conscious when a person is actually aware of being in that state