Neurobiology of learning, memory and cognition: Blindsight & attention Flashcards
Distributed neural networks
-
Cognitive and emotional functions of association cortex
-
Divisions of the cerebral cortex
Functions of the association cortices
Sensory, motor and association cortex.
Each sensory modality has its own unimodal association cortex.
3 main polymodal association regions:
- prefrontal association cortex (higher motor functions, planning of action, attention)
- limbic association cortex (emotional & mnemonic functions)
- parieto-temporal-occipital cortex (higher polymodal sensory functions including language)
PET scanning
Measures cerebral blood flow
Patient is given a radioactive atom with a v short half life intravenously (e.g 15O2 in water)
Collisions of a positron with an electron cause emission of 2 annihilation photons at 180degrees to one another.
Detectors placed around the head detect location
Greater the blood flow- greater the number of annihilation photons.
‘What’ pathway of visual processing
Directed ventrally from occipital cortex into temporal lobe
Object recognition, colour, shape
Area V4
‘Where’ pathway of visual processing
Directed dorsally from occipital cortex to into parietal lobe.
Crucial for spacial perception, visuomotor performance
Area V5
Blindsight
Damage to primary visual cortical regions produces blind spots or scotomas.
Sometimes, patients e.g DB are able to orient ‘unseen’ stimuli if forced to guess.
Weiskrantz & Warrington showed that DB:
- if forced to guess where a brief stimulus had occured, was much better than chance, but would deny that he could detect the event.
- had an unconcious ability (though limited capacity) to detect different shapes & wavelengths/
Therefore evidence for restricted cortical processing in blindsight. Possibility = the LGN, or the superior colliculus & pulvinar, project to subsequent regions of visual cortex, bypassing V1.
PET studies in blindsight patients show increased blood flow in V5 during visual motion stimulation in the patients scotoma.
Proposed mechanism of visual conciousness
Depemds on interactions between V1 and V5? Lesions in either prevent conscious awareness of motion perception.
Back projections from extra-striate regions to the striate cortex may play a key role?
Attention
Selective attention for features: Attending to particular attributes of stimuli (speed, colour, shape) lowers detection thresholds for those stimuli.
Spatial attention: Attending to a particular location in space improves detection of events in that location, and level of visual analysis performed on those events
Attention also enhances reaction times.
Overt visual attention
Selectively attending to an item or location over others by moving the eyes to point in that direction. Can be detected in the form of eye movements
Covert visual attention
Attending to part of the visual field without shifting eyes to focus on that area
Detection thresholds
A stimulus (e.g speed, colour, shape) that is less intense than the sensory threshold will not elicit any sensation.
Endogenous attention
When actively choose to attend to something
‘Top down’
Uses previous experience & knowledge of the world to direct attention to relevant stimuli.
Exogenous attention
When stimuli in the environment ‘grab’ our attention because bright, moving etc.
‘Bottom up’
Neglect
Caused by damage to the inferior parietal cortex within the posterior parietal lobes.
Patient appears to ignore stimuli in one side of space.
- often polymodal
- not a simple sensory problem- patients do not suffer specific sensory problems, and are generally unaware of the problem.
- often recovers over time- leaving extinction, where only the ipsilateral stimulus is detected. Probably due to attentional competition
- Can occur for mental spatial representations e.g Bisiach et al, Piazza del Duomo.
- more often seen following right hemisphere damage
- can be viewer or stimulus- centred.
