• Created by: 10dhall
  • Created on: 18-05-19 19:14
Key reading - Sip et al 2008 - ethical implications
Many studies have concluded that fMRI has been successfully used to detect lies. at least 2 companies have been made to sell lie detection fmri to people. Raises major ethical implications as people are being mis sold expensive equipment
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how are fmri outputs imaged
as a time series, with 3 levels of spatial zoom/repres
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what 4 scans are taken in fmri studies
survey:image to plan scan. reference:image to calibrate scanner. t1:anatomical image to study brain in high detail. t2: functional scan using BOLD to map activity(worse res than t1, no structure, 1 image every few seconds)
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what is volume in fmri
3d scan of the brain
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what is slices?
2d scan of the brain- many in a voxel
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what is a voxel?
3d pixel- 3mm- many of these make a slice
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what is the bOLD amplitude response to stimulus?
stimulus pres- haemodynamic lag- primary response peak - post stimuli shoot (under baseline)
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issue regarding temporal?
bold responses last roughly 10 seconds,stimuli can last less that 1s. it takes 15-20s to return to baseline. repeating stimuli can lead to conditions merging data - real time fmri is impossible
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how do we conduct a glm?
create graph of stim timings. compare bold signals, modelled separate, using a line for each condition. have a graph per voxel. then use linear regression
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measures of noise and how they're countered?
head movements, eyes opening, other brain processes. The GLM measure fits an estimate of activity whilst cancelling noise
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T statistic?
regression coefficient/noise - how well the model fits/ what it can't explain - if T is high= good fit and likely to be activated by task
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How is activity found in bold?
Measures contrasts and differences between 2 different conditions of activation maps e.g activity compared to rest or 2 similar activities - actives should be very similar apart from 1 thing that separates conditions - that process is meaning of acts
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what can be compared in FMRI?
stimulus properties, task performance, cognitive states, ilness
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what does its temporal not allow us to do?
cannot measure hierarchy of processes or the origin/causation. we use eeg to see the temporal because its temporal is good or TMS
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Combining groups BOLD data?
Sometimes Bold activation maps are combined for groups.- this gives a total but is not good because everyones brains work differently and some peoples brains are shaped differently.
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Pros of FMRI
Reveals areas activated by task, their size and location
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cons of FMRI
results depend on model and effectiveness of contrast. assumptions: amplitude is same across trials (changes). shape+delay of HRF same (elderly+ill+others= diff), if signal doesn't match HRF it isn't measures
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how does fmri analyse complex q's e.g, amount of activation
when neural/voxel responses are more distr or patterned. GLM cannot direct each area - decode the voxel to see more spatial resolution
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Define GLM outline
finds clusters of activation- needs multivoxel clusters- smooths over space
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What is MVPA? multi voxel pattern analysis?
voxel strength recorded for conditions. placed in pattern and algorithm. train algo on subsection to predict each condition. distinguish cond using algo to show which voxel in which cond. validate over many conditions-increases spatial
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Xu - 2017 - bilingual
classify language processes localisation in bilinguals- idea that language segregation is essential to speak and not cross-talk. found independent and shared voxels for each language - showing separation and validating firm
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why does FMRI require stillness
voxel size is 3mm - if the head moves more than this it will move the voxels out of place and create confusing analysis- restricts tasks and populations able to study - however this can still be fixed with algorithm
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how are fmri outputs imaged


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what 4 scans are taken in fmri studies


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what is volume in fmri


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what is slices?


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