Book: the imaged brain 2

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  • Created by: CanveySam
  • Created on: 07-05-15 13:20
What are the main problems with cognitive subtraction?
Regions of activity need to be compared to an appropriate baseline 1) Assumption of "pure insertion" i.e. adding a task/extra component does not affect the operation of earlier components, however this ignores interaction effects. 2) So a baseline task is
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Name 3 other methods in addition to cognitive subtraction
Cognitive conjunctions/factorial design, Parametric design, Functional integration
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What is the advantage of cognitive conjunction over cognitive subtraction?
Baseline task still needed, but risk of interaction effect is reduced
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How does cognitive conjunction design work?
CC requires set of tasks that have a particular component in common. Then look for regions of activation that are shared across several different subtractions, rather than relying on one single subtraction
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Give an example of cognitive conjunction/factorial design
Why can't we tickle ourselves (Blackmore et al 98). 2 factors: touch (felt/not) and self-mvt (moved/not)
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What is the parametric design?
Variable is continuous not categorical i.e. brain associations not differences
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what is the functional integration design?
how different regions communicate with each other e.g. task shows 'effective connectivity' cf specialisation
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which is the best design for one factor?
parametric or cognitive subtraction
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Pro and con of blocked design?
Pro: strong BOLD contrast, high signal to noise, simple design; Con: practice/fatigue effect
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Pro and con of event-related design?
Pro: No practive/fatigue effect; Con: weaker BOLD contrast, lower signal-to-noise, complex design
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what is meant by a 'session'?
A scanning session; all the data collected from the participant. Usually a structural scan and few functional scans
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What is meant by a 'run'?
A continuous period of scanning, consists of a specified number of volumes
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What is meant by a 'volume'? (image)
Set of slices taken in succession: a 3D spatial image with a temporal dimension. Expressed in TR
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What is meant by an 'epoch'?
a period when a certain condition is presented. Epochs can be grouped (blocked) or random (event-related)
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5 stages when analysing fMRI data
1) individual differences; averaging over many participants 2) correction for head movement 3) stereotactic normalisation 4) smoothing 5) statistical comparison
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What is stereotactic normalisation?
the mapping of individual differences in brain anatomy onto a standard template
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what is smoothing?
redistributing brain activity from neighbouring voxels on the assumption that cognition does not occur in single voxels. This enhances signal-to-noise ratio
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List the three issues implicated in interpretation
1) Inhibition v excitation 2) activation v deactivation 3) Necessity v sufficiency
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What is the issue of inhibition v excitation?
Activity can be inhibitory or excitatory i.e. an inhibited region could be mistaken as a region of activity
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What is the issue of activation v deactivation?
Merely refers to a difference between two conditions; doesn't suggest any direction
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what is the issue of necessity v sufficiency?
Are active regions critical to the task?
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Why should we be cautious with fMRI?
Can only show correlational not causal evidence of brain activity. Rare for single area to be implicated; when more than one task then hard to say which area is critical to task
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Card 2

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Name 3 other methods in addition to cognitive subtraction

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Cognitive conjunctions/factorial design, Parametric design, Functional integration

Card 3

Front

What is the advantage of cognitive conjunction over cognitive subtraction?

Back

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Card 4

Front

How does cognitive conjunction design work?

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Preview of the front of card 4

Card 5

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Give an example of cognitive conjunction/factorial design

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