Task 6 experimental designs & analysis Flashcards
Forms of stimulus presentation
- block design
- event-related design
- mixed design
Blocked design:
- recorded neural activity is integrated over “block” of time during which pp is presented a stimulus /performs certain cognitive task
- recorded pattern is compared to other blocks recorded while doing same/different/no stimulus
Event-related design
- across experimenta; trials, BOLD response is linked to specific events (e.g., stimulus presentation)
–> can be used at great range of experiments
Advantages Blocked design
- more power: ability to detect small but significant effects
- relatively easy to analyze
- required for studying state-based processes
- support subject compliance in cases where condition switching is disruptive
Disadvantages Blocked design
- not all processes can be blocked: no way of knowing in advance how events should be grouped / task requires stimulus to be infrequent and unexpected
- minimally compatible with typical behavioural and electrophysiological methods
- may promote unintended subject strategies, anticipation and habituation
- requires pre-specification of limited set of experimental comparisons
Advantages of event-related designs
- allows for random intermixing of trial types
- can provide estimates of HR time-course
- allows for separation of HR from artifact events
- can be categorized post-hoc to conduct multiple experimental contrasts
- possible to study unusual events (e.g., IDD)
- more closely related to typical design structure of most cognitive psychology experiments
Disadvantages of event-related designs
- reduced statistical power
- more difficult to analyze
- can’t be used to study state-based processes
rapid stimulus presentation/ rfMRI
- method to overcome problem of event-related designs being time-consuming: ISIs is shorter than duration of HRF generated from previous stimulus
Problem: reduced ability to estimate the problem of linearity: response to stimuli presented in a sequence is the sum of the response to the stimuli presented separately –> overlapping HRFs
Solution: varying ISIs
Behaviourally driven fMRI
- scanning individual in an MRI scanner and observe variation of BOLD response related to spontaneous activity or resting state
Advantage: variable ISIS
Disadvantages:
- dependent on each subject’s performance and inter-subject variability
- number of events per condition (=> statistical power) is largely unknown beforehand
- limitations related to linearity properties of overlapping
List of methods and comparison strategies
- cognitive subtraction
- cognitive conjunction
- factorial designs
- parametric design
Cognitive subtraction
activity in control task is subtracted from activity in experimental task
- interpreted relative to baseline
- useful when combined with blocked design –> allows simple modeling of BOLD response with robust and reproducible results
Assumptions:
- pure insertion: adding extra component doesn’t change operation of earlier components
Parametric designs
- variable of interest is treated as continuous dimension rather than categorical distinction –> measuring association between brain activity and changes in variable of interest
- no baseline condition necessary
- allows separation of areas from other brain areas responsible for basic cognitive processes
Factorial design
- allows to test for interaction between components: subjects performing task in which cognitive components are intermingled first and then separated in paradigm
- based on neuropsychological evidence for precise definition of task component and complementary behavioural data
Assumption: linearity betwen BOLD responses resulting from conditions
Cognitive conjunction
variation of factorial design:
- 2+ conditions of fMRI paradigm share the same cognitive component of interest
- requires the identification of a set of tasks with a particular component in common –> allows to look for regions of activation shared across several different subtractions rather than relying on single subtraction
functional integration
regions responds to a limited range of stimuli/conditions -> distinguishes the area from responsiveness of neighbouring regions
- way in which regions communicate with each other
- models how activity in different regions is interdependent
difference to localization:
- not necessary to assume that regions are solely resonsible for performance on a given task or that other regions may not also resopnd to same stimulus/condition
