Hemodynamic neuroimaging Flashcards

Question

What is the Rapid counterbalanced event-related design?

Answer 1

• ISI = 0 or not longer than the trial duration • Conditions alternate in pseudo-random order: each condition follows each condition an equal number of times (counterbalancing) • Peak in a difference of signal between conditions when particular condition occurs frequently in short period of time • Reasonable sensitivity and power • > Alternating design and slow design • < Block design • Estimation possible when one of the conditions = rest • < Slow design • Trial order similar to that of most behavioral experiments

Answer 2

No dichotomy between block and event-related • Distinction = fuzzy • Intermediate approaches • E.g. block length of 4-6 s; manipulation of probability of conditions • Many different designs and extensions developed and used • Condition-rich event-related design: multi-voxel pattern analysis • fMRI adaptation – also known as repetition supppresion

Answer 3

• To activate particular mental processes of interest • Task depends on question • Comparing conditions different in both stimuli and task violates subtraction method assumptions • When interested in stimulus effects • No need for a behavioral response, in contrast to behavioural study • Possible tasks without a stimulus-related response: • Passive viewing • Orthogonal task • Very hard to avoid criticism about confounding task effects

Answer 4

• Few problems for fNIRS • Most problems for fMRI: • Visual stimuli: Goggles, projection on a screen, or screen seen through a mirror • Eye movement control: useful but difficult • Auditory stimuli: noise of scanner (can be 120 dB!), interleaved data acquisition • Verbal responses: interference from scanner noise, confounding head movements during speaking • MRI-compatible equipment = nonmagnetic and certified for use in a strong magnetic field

Answer 5

• Programming • Need to synchronize MRI data acquisition with experiment by reading in trigger signal from scanner • Presenting stimuli is more complicated (e.g., specific hardware) • Reading behavioural response: no keyboard, other hardware is needed • Ethical approval takes longer than for behavioral experiment • Good preparation is critical because scanning is costly • Keep detailed logbook of *everything* that happens

Answer 6

• Safety issues • Practice session in dummy/mock scanner for special populations like children • Handedness • Gender • Number • Depends upon expected effect size and signal to noise ratio • Prior estimate of power is strongly advised, but not easy to determine • Variation in literature between only 3-5 participants (when effect is large, can be demonstrated in single subjects, and data collection per subject is intensive) up to hundreds of participants.

Answer 7

• Pre-processing not or very limited for behavioural data, but very important for imaging data • Pre-processing is not part of statistics (but can strongly influence stats)

Answer 8

• Knowledge/background of the researcher • Flexibility researcher wants • Potential preference for operating system • Expertise in lab of researcher

Answer 9

Quality control • Continuous point of attention • Automatization is efficient, but creates large distance between experimenter and data without good quality control • When starting: cut analysis in small pieces and run step by step • Large problems often already detected during scanning itself • After scanning, image files copied to work station but check them • File names • File sizes (all runs of equal length should be equal size) • Inspect some time points

Answer 10

• Some displacements cannot be corrected offline • E.g. abrupt motion during TR àlarge shift of all other slices acquired after • Motion decreases image quality due to instabilities in fMRI signal • Alters magnetic field and its inhomogeneities and history of excitation of nuclei • Takes much longer than actual movement to stabilize again • Amount or type of motion can be related to experimental conditions • E.g.: complex movement for a condition --> small head movement • Hard to dissociate neural activity from motion artefacts/ confounds

Answer 11

External quality control through transparency and reproducibility • Questionable research practices and relatively low rate of reproducibility • In fields where statistics play a big role • When effect sizes are small • When many different research groups • Positive: Many neuroimaging key findings have been documented over and over again (e.g., presence of face-selective regions) • Negative: Chance of success to replicate a randomly chosen neuroimaging paper will be lower than it should be • Number from psychology: effect size in replication typically half of effect size in original report

Answer 12

• Large degree of flexibility and possibility for exploration in analysis • Each choice impacts results • All choices together can have huge influence on final results • Worst case, and not acceptable: some of the choices influenced by knowing about the results obtained with these choices --> circular analyses • Insufficient statistical power • Due to insufficient number of participants given the typical effect size • Increases possibility of false negatives • Increases potential impact of questionable research practices, and thus possibility of false positives • e.g. decision to take out 1 participant because of “bad data” (based on a priori criterion or on circular reasoning) will have more impact with a lower number of participants • Decreases trustworthiness of effect size estimates in studies • Need for a priori power analysis (even though it is difficult, e.g. because effect size is also determined by data quality)

Answer 13

• Methods sections as complete and transparent as possible • In its asymptote very similar to a preregistered study • Analysis tools and data made available (e.g., Open Science Framework) • More replication efforts necessary • More focus upon meta-analytic approaches and innovative tools to do so • More data sharing