TASK 8 - LESION Flashcards
lesion studies
= study brain lesion (caused by an injury or disease) induced behavioural impairments
- brain activity as dependent variable
- -> want to establish causal relationship between brain damage and impaired task performance
process
- injury/disease
- brain lesion (= brain area is impaired or non-existent)
- neuropsychological testing (e.g. reaction time)
- specific impairment in behaviour or cognition observed
- insights into original function of brain area revealed
dissociation
= performance on one task is impaired while performance on second isn’t
- functions/processes are then dissociable/separable
- -> cognitive neuropsychology: difficulty in one domain relative to an absence of difficulty in another domain can be used to infer independence of these domains (= separate neural resources)
- might reflect two different populations of interspersed neurones
- cannot conclude that it’s the only function of these neurones
- always need a range of relevant tasks (not just 2) to properly interpret spared + impaired performance
dissociation
- single
= patient with lesion X shows severe impairment in task A but not in task B; patient with lesion Y does not show any impairment (neither A nor B)
- -> non-reciprocal dissociation
- or patient with lesion Y always impaired in both task
a) classical single dissociation: patient performs entirely normal on one task
b) strong single dissociation: impaired on both tasks, but significantly more impaired on one of them
single dissociation
- interpretation
A. hierarchal relationship: 2 functions are separate to some degree, but one of them is necessary for the other (e.g. blindness & inability to read visual material)
B. task A + B may use different cognitive processes with different neural resources (can’t conclude this)
C. task A + B may use same resources but one requires more of it than the other –> task-resource artefact (minimised by double dissociation)
D. single dissociation occurs because patient performs one of the tasks suboptimal –> task-demand artefact (control for IQ, instructions)
single dissociation
- localisation
- lesion in region X produces impairment on task A, not B
- lesion in region Y produces no impairment on either task
- -> lesion X is not causing general deficit, but specific
- because 2nd lesion in other location doesn’t produce the impairment
- -> lesion in question doesn’t produce impairment in all tasks
- because relatively good performance seen in 2nd task
- leaves open the possibility that lesion has the effect because it is simply more important in some general sense (not because disrupted area is involved in the particular function)
dissociation
- double
= lesion X is impairing task A but not B, while lesion Y impairs B and not A
- -> reciprocal dissociation
- 2 single dissociations that have a complementary profile of abilities
- each lesion-impairment serves as control for the other
- different claims on how specific a particular lesion links to a specific function
double dissociation
- interpretation
- evidence that 2 functions are relatively separate/independent
- in each lesion we learn that it is involved in a particular function, but not another
- -> e.g. Broca’s aphasia
doble dissociation
- localisation
- lesion in region X produces impairment on task A, not B
- lesion in region Y produces impairment on task B, not A
- firmer grounds for localisation of function
association
= consistent co-occurrence of 2 or more impairments
- suggest one underlying process, but may be due to proximity
association
- localisation
- single region is necessary for different functions
- but functions may be separable but mediating brain areas in close proximity
- when impairment in both functions usually but not always co-occurs (= sometimes dissociable)
single-case studies
=
single-case studies
- assumptions
1) fractionation assumption: damage to brain can produce selective cognitive lesions
- more likely if neurones performing a specific task are clustered rather than distributed
- partly met
2) transparency assumption: lesions affect one or more components within the pre-existing cognitive system but don’t result in the creation of a new cognitive system; intact regions continue to function in same matter as before
- if old function reinstated without creating a whole new way of performing the task
- more likely if brain lesioned in adulthood
3) universality assumption: all cognitive systems are basically identical; individual is representative of the population to make generalisations to normal cognition
- individual differences cannot be due to qualitative differences
- comparability between premorbid + postmorbid cognitive systems, not where they are located
- more likely if brain lesioned in adulthood + when studied soon after the injury (or if cognitive profile remains stable over time)
single-case studies
- reasons to use
• In non-damaged peeps it’s feasible to average group results bc. the only difference btw participants is noise
• In lesioned peeps, the differences in performance may be attributable to differences in lesions rather than btw patient noise
o Averaging across participants not possible
• Determining where in the cognitive system (not regionally) the lesion is can only be determined by empirically observing each case in turn
• Even if we were to find a group of identical patients, the study becomes a series of single case studies
• Provide valid data with which we can test, adapt & develop a cognitive theory
o Can generalise to a model of normal cognition, but not to another case
group studies
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