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Summary Task 6 - Design & Analysis of Neuroimaging Experiments $3.75
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Summary Task 6 - Design & Analysis of Neuroimaging Experiments

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Summary of Task 6 of Methods of Cognitive Neuroscience

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  • March 17, 2024
  • 9
  • 2023/2024
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TASK 6: DESIGN & ANALYSIS OF
NEUROIMAGING EXPERIMENTS
BLOCK DESIGN

 Stimuli that belong together in one condition could
be grouped together
 Alternation of two conditions – AB block
 A cycle correspond to two epochs of each condition
 Advantages: (1) more power than event-related designs,
more able to detect significant but small effects, (2)
required for studying state-based processes, (3) better
subject compliance when condition switching is disruptive, (4) easy to analyse
 Disadvantages:
 Impossible if we don’t know in advance how events should be grouped
 Sometimes categories are defined by each participants and cannot be blocked
together beforehand
 Sometimes task requires that they events unexpected & occur infrequently
 Can’t estimate time-course of hemodynamic response
 May promote unintended subject strategies, anticipation, habituation
 Require pre-specification of a limited set of experimental comparisons

EVENT-RELATED & BEHAVIOURALLY DRIVEN DESIGN

 Different stimuli / conditions could be interspersed
with each other
 Different intermingled conditions are subsequently
separated out for the purpose of analysis
 Advantages:
 Enable much wider range of experimental designs
 More closely related to typical design structure of most cognitive psychology
experiments
 Can detect transient variation in haemodynamic responses, which allows temporal
characterisation of BOLD signal changes  haemodynamic response function
(HRF)
 Brain regions correlated to the task can have different HRF
 Allows for analyses related to individual responses to trials
 Provides the means to analyse neural correlates of behavioural responses
 Less sensitive to head motion artifacts
 Can be used to assess practice effects
 Allows for randomisation of order of presented conditions

,  Can vary time between stimulus presentation reducing subject’s ability to predict
when & what will happen  maintains attention level across experiment

RAPID ERFMRI

 Variation in which the interstimulus interval (ISI) is shorter than the duration of the HRF
generated from previous stimuli  next stimulus begins, before the previous HRF is
back at its baseline
 Easier to understand neural correlates of many
psychophysical experiments
 Increased number of stimuli presented per time
unit  enhances statistical power
 FMRI responses – mixtures of several stimuli /
conditions
 Can be unmixed through deconvolution
 Advantages: (1) allow for random intermixing of trial types, (2) can provide estimates of
HR time-course, (3) allow for separation of HR from artifact events, (4) conditions can
be categorised post-hox, (5) possible to study unusual events, (5) designs directly
compatible with other methodologies
 Limitations: (1) reduced ability to estimate HRF properties of a single stimulus, (2)
problems related to linearity vs. non-linearity of BOLD interaction, (3) reduced
statistical power, (4) unsuitable when conditions have large switching cost, (5) more
difficult to analyse
 Linearity assumption – BOLD responses can be seen for each specific type of stimulus
& there is no interaction between them
 2nd limitation: stimuli are faster than BOLD signal can be shown  BOLD signals of
different stimuli overlap BUT during data analysis we can separate the BOLD
signals of each stimulus from the next one
 Slow fMRI – just the normal fMRI




MIXED DESIGNS

 Combination of block & event-related designs
 Can provide information relating to maintained vs. transient neural activity during
paradigm performance

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