TASK 6 - DESIGN & ANALYSIS Flashcards
experimental design
= consists of manipulation the subject’s experience and behaviour that is likely to produce a BOLD response
- data acquisition, results, interpretation all depend on thorough experimental design
- what to manipulate: stimulus kind + properties, stimulus timing, subject instructions
- goal is to test specific hypotheses
cognitive subtraction
= compare brain activity in task that uses a particular cognitive component (A+B) to brain activity in baseline task that doesn’t (A) –> infer which region is specialised for this particular component (B)
- assumes pure insertion: addition of B does not change the character of A
- (A+B)-A=B –> stimulus condition-control condition = change in conditions
- statistical analysis of each voxel
cognitive subtraction
- application
- useful especially in combination with blocked designs, allowing for simple modelling of BOLD response, resulting in robust + reproducible results
cognitive subtraction
- limitations
- pure insertion: if violated, we would have an interaction effect that makes imaging data ambiguous at best
- choice of baseline task: strong impact on data that is obtained
- -> requires good cognitive theory about the elements that comprise the task
- ideally: baseline should be as similar to the experimental task as possible
cognitive conjunction
= do multiple subtractions; use more than one control condition
- identify a set of tasks that has a particular component in common (look for regions of activation that are shared across different subtractions (rather than relying on a single)
- two different tasks that have one thing in common (what area is activated by both tasks, shows us our goal (face processing of apes vs. humans))
1) (A+B+AB)-A=B+AB
2) (C+B+CB)-A=B+CB - -> different than subtraction (one thing different, rest the same)
- remedy for pure insertion (cognitive subtraction)
factorial design
- can study main + interaction effects
- main effects: e.g. effect of attentional load, irrelevant of motion –> (A+B)+(C+D)
- interaction effects: e.g. is the difference between motion (vs. no motion) different under low attentional load (vs. high load)? –> (A-B)-(C-D)
cognitive conjunction + factorial design
- assumptions
- doesn’t assume pure insertion: terms will be different for each pair of subtraction
- -> technique is useful for studying cognitive interactions
- linear relationship between BOLD response resulting from the conditions, otherwise some finding may be contaminated by non-predicted interactions
parametric design
= one feature of the stimulus (parameter) stimulus is varied in a continuous way
- measure association between brain activity + changes in the variable of interest
- allows to isolate rhythms of brain, level of activity
- low level of stimulus can be control condition of higher levels –> similar conditions
parametric design
- problems
- increasing a parameter over a certain limit can involve recruiting other cognitive processes that are not necessarily present at lower levels of performance of the neural system
functional specialisation
= implies that a region responds to a limited range of stimuli, distinguishing it from neighbouring regions
- most studies focus on functional specialisation
- -> not necessary to assume that the region is solely responsible for performance on a given task
- -> not necessary to assume that other regions may not also respond to same stimuli
functional integration
= the way in which different brain regions communicate with each other
- model how activity in different regions is interdependent
- used to infer effective/functional connectivity between regions when performing a task
- correlate different regions of brain activity with each other
resting state paradigm
= behaviourally driven fMRI = no task, just chill
- fluctuations in brain activity are little more than noise
- BUT, in brain regions that are functionally connected, the noise levels tend to correlate together
- -> allows to identify sets of networks
stimulus timing
= determine presentation/timing of stimuli to get optimal design
stimulus timing
- block design
= repetition of relatively long blocks with stimuli that are homogenous within one block
- stimuli that belong together in one condition are grouped together
- blocks have duration that usually exceeds the length of the hemodynamic response (15-30s)
- blocks invoke cognitive state; consist of multiple trials sampled from same condition in rapid succession
- BOLD response to condition A = collective average of trial responses
- -> cannot distinguish between differences within the block, because we aim to see the effect of whole block/condition
block design
- Trojano study
- study whether mental imagery and perception make use of same brain areas
a) mental clock test: requires mental imagery of two clocks and mental comparison (only auditory presentation of clocks)
b) perception task: does not require mental imagery and comparison because clocks are visually presented
c) syllable counting task: control task with same attentional load as mental clock test but not requiring mental imagery
