Experimental Designs in fMRI Flashcards
What is an independent variable in an experiment?
The variable manipulated in an experiment to generate changes in the measured response.
Define dependent variable.
The measured variable of interest in an experiment.
Differentiate between categorical and continuous variables.
Categorical variables have discrete values, while continuous variables have an infinite number of values.
What is the purpose of an experimental design in fMRI?
It organizes an experiment to effectively test research hypotheses, especially crucial in fMRI due to its high cost.
How is internal validity defined in a study?
Internal validity is achieved if a study produces one and only one explanation of the results.
Explain external validity in the context of a study.
External validity refers to the generalizability of results beyond the research context, from sample to population, from one study to another, and from a study to the real world.
What is the impact of extraneous variables on internal validity?
Extraneous variables interact with the independent variable and its manipulation, worsening internal validity.
Describe the trade-off between internal and external validity.
There is a trade-off between internal and external validity, increasing one will decrease the other, necessitating a balance.
What characterizes an experimental condition?
An experimental condition contains tasks or stimuli relevant to the research hypothesis.
What is the purpose of a control condition (baseline)?
A control condition provides a standard for comparison with experimental conditions, ensuring they are not too distant or similar.
What is the pure insertion assumption in subtraction designs?
It assumes that a specific cognitive process can be inserted into another set of cognitive processes without altering their nature.
How is a conjunction design used in fMRI studies?
It isolates the same process by multiple separate comparisons and tests for common activation in several independent contrasts.
What is the aim of parametric designs in fMRI?
Parametric designs vary a stimulus parameter of interest on a continuum, offering flexibility in testing relations between BOLD and the parameter.
What does a factorial design with categorical factors allow in different studies?
It allows the verification of the pure insertion assumption in different studies, modeling interaction between factors.
What is PPI, and what factors does it involve?
Psychophysiological Interactions (PPI) is a parametric factorial design involving a psychological context and a physiological source, requiring knowledge about neurobiological plausibility.
How do block designs capture brain responses?
Block designs examine responses to a series of similar stimuli, capturing sustained tonic responses.
Differentiate between epoch and event-related models in block designs.
Epoch models involve sustained periods of stimulation, while event-related models consist of impulses.
What are advantages of block designs in fMRI experiments?
Block designs are simple, minimize task switching, are robust to uncertainty in timing, and allow straightforward analysis.
What is a disadvantage of event-related designs compared to block designs?
Event-related designs are less efficient for detecting effects than block designs.
What is the problem of multicollinearity in fMRI data analysis?
Multicollinearity occurs when regressors in the design matrix correlate with each other, making the interpretation of GLM results challenging.
How are adaptation and refractory effects employed in fMRI studies?
They are used as indices of brain function, with repetition suppression revealing brain regions associated with adaptation.
What is reverse inference in fMRI?
Reverse inference involves inferring the occurrence of a process based on the activation of a certain brain region, which is logically invalid for various reasons.
What criticism is associated with brain-behavior correlations in fMRI studies?
Some argue that reported brain-behavior correlations are impossibly high, potentially misleading interpretations.
How is susceptibility artifact defined in fMRI?
Susceptibility artifacts result from differences in magnetic field strength near substance interfaces of different magnetic susceptibility.
How does the presentation of a brain image influence scientific reasoning, according to McCabe & Castel (2008)?
Participants are more likely to judge a statement as valid when a brain activation map is included in the article.
What is a notable advantage of fMRI?
FMRI is non-invasive and does not require ionizing radiation, making it safe for repeated use.
What is a limitation of fMRI in terms of time resolution?
fMRI has low time resolution, but it can be combined with EEG to address this limitation.
Why is fMRI considered an indirect measure of neural activity?
It measures changes in blood flow and oxygenation, which indirectly reflect neural activity.
What is a potential issue with the heavy dependence on choosing a good baseline condition in fMRI studies?
Too close to active conditions may result in false negatives, while too far may lead to false positives.
What term describes the correlation between regressors in the design matrix in fMRI analysis?
The problem of multicollinearity arises when regressors correlate with each other.
What does fMRI evidence need to be supported by to establish causality?
fMRI evidence needs further converging causal evidence, such as from neuropsychology or transcranial magnetic stimulation (TMS).
How does susceptibility artifact occur in fMRI?
Susceptibility artifacts result from differences in the magnetic field strength near interfaces of substances with different magnetic susceptibilities.
According to Lilienfield et al. (2015), why should certain terms be avoided in neuroimaging literature?
The use of certain terms may lead to wrong interpretations and assumptions, affecting both popular and scientific reception.
What is reverse inference in fMRI, and why is it considered logically invalid?
Reverse inference involves inferring a process based on the activation of a brain region, but it is logically invalid due to the lack of a one-to-one correspondence in the mind-brain relationship.
What is the purpose of multiple comparison correction in fMRI?
Multiple comparison correction is essential in neuroimaging data to account for the high number of statistical tests and reduce the risk of false positives.
What are the advantages of block designs in fMRI experiments?
Block designs are simple, minimize task switching, have maximum efficiency, and are robust to uncertainty in timing.
What is a limitation of event-related designs compared to block designs?
Event-related designs are typically less efficient for detecting effects than block designs.
Why is fMRI considered an indirect measure of neural activity?
fMRI measures changes in blood flow and oxygenation, which are indirect indicators of neural activity.
What is the main criticism associated with brain-behavior correlations in fMRI studies?
Some argue that reported brain-behavior correlations are impossibly high and may not accurately reflect underlying cognitive processes.
According to McCabe & Castel (2008), how does the presentation of a brain image influence scientific reasoning?
Participants are more likely to judge a statement as valid when a brain activation map is included in the article.
What is a notable advantage of fMRI?
fMRI is non-invasive and does not involve ionizing radiation, making it safe for repeated use.
What is a limitation of fMRI in terms of time resolution?
fMRI has low time resolution, but it can be complemented by combining it with EEG.
Why is the choice of a good baseline condition crucial in fMRI studies?
The choice of a good baseline condition is crucial as being too close to active conditions may lead to false negatives, while being too far may result in false positives.
What term describes the correlation between regressors in the design matrix in fMRI analysis?
The problem of multicollinearity arises when regressors in the design matrix correlate with each other.
What does fMRI evidence need to be supported by to establish causality?
fMRI evidence needs to be supported by further converging causal evidence, such as findings from neuropsychology or transcranial magnetic stimulation (TMS).
What are susceptibility artifacts in fMRI, and how do they occur?
Susceptibility artifacts result from differences in magnetic field strength near interfaces of substances with different magnetic susceptibilities, affecting brain regions proximal to these interfaces.
According to Lilienfield et al. (2015), why should certain terms be avoided in neuroimaging literature?
Certain terms may lead to incorrect interpretations and assumptions in both popular and scientific reception.
What is the logical issue associated with reverse inference in fMRI?
Reverse inference involves inferring a process based on the activation of a brain region, but it is logically invalid due to the lack of a one-to-one correspondence between mind and brain.
Why is multiple comparison correction important in fMRI data analysis?
Multiple comparison correction is crucial to account for the high number of statistical tests in neuroimaging data, reducing the risk of false positives.
What are the advantages of block designs in fMRI experiments?
Block designs are simple, minimize task switching, have maximum efficiency, and are robust to uncertainty in timing.
