1. Study Design and Efficiency Tom Jenkins Catherine Mulvenna

2. How the class will go… Choosing the right study design for your experimental question (Catherine) Choosing the right study design for your experimental question (Catherine) How the design affects your efficiency (Tom) How the design affects your efficiency (Tom)

3. What is involved in study design? How you present the data How you present the data Block Vs event-related design Block Vs event-related design How you present the experimental question How you present the experimental question Psychological validity Psychological validity fMRI is as worthwhile as the design of the experiment using it. fMRI is as worthwhile as the design of the experiment using it.

4. A BLOCK: a series of trials is presented during a discrete epoch of time. A BLOCK: a series of trials is presented during a discrete epoch of time. The most commonly used fMRI paradigm is blocked design BLOCKED DESIGN: different conditions are assigned to different blocks. The signal acquired in different blocks is contrasted. BLOCKED DESIGN: different conditions are assigned to different blocks. The signal acquired in different blocks is contrasted.

5. For good reviews see Binder & Rao 1994; D’Esposito et al., 1999 For good reviews see Binder & Rao 1994; D’Esposito et al., 1999 Assumptions of the Block Design: "Neural structures supporting cognitive and behavioural processes combine in a simple additive manner." Assumptions of the Block Design: "Neural structures supporting cognitive and behavioural processes combine in a simple additive manner." Also you may not be able to test certain things with such a design… Blocked design  e.g localise a specific brain region showing the response to one type of stimulus (e.g. faces vs houses)

6. Event Related Design Types of trials are interleaved and each trial is modelled separately as an ‘event’ e.g. AABABBAB Types of trials are interleaved and each trial is modelled separately as an ‘event’ e.g. AABABBAB

7. Sequencing of events Deterministic designs: the occurrence of events is pre-determined e.g. a blocked design or alternating design (all the probabilities are zero or one ) Stochasticdesigns: the occurrence of an event depends on a a specified probability e.g. random or permuted design Stochastic designs can be stationary or dynamic Blocked Alternating 12345678 10 20 30 40 50 60 70 80 Random Permuted

8. Advantages of efMRI Can randomise or counterbalance trial order to reduce contextual bias and minimise differences related to cognitive ‘set’ or strategy use. Can randomise or counterbalance trial order to reduce contextual bias and minimise differences related to cognitive ‘set’ or strategy use. Some experimental designs cannot be blocked e.g. oddball designs. Some experimental designs cannot be blocked e.g. oddball designs. Can use post-hoc classification of trials e.g. separately model trials with correct or incorrect responses, following post-scanning testing or depending on subjective perception. Can use post-hoc classification of trials e.g. separately model trials with correct or incorrect responses, following post-scanning testing or depending on subjective perception. Improves temporal resolution such that you can look at events on a shorter time scale. Improves temporal resolution such that you can look at events on a shorter time scale.

9. Disadvantage of efMRI Typically less efficient than blocked designs - Tom. Typically less efficient than blocked designs - Tom.

10. “the brain may be gray and nondescript on the outside, but on the inside it's a well- practiced liar.” Psychological validity

11. Psychological Validity in fMRI Studies Validity: Is the test measuring what it is supposed to measure? Validity: Is the test measuring what it is supposed to measure? Ask others what they think alternative explanations for your results are. Incorporate these into your study. Ask others what they think alternative explanations for your results are. Incorporate these into your study. E.g. of poor validity… E.g. of poor validity…

12. When deciding on the tasks… A study’s design is only as good as the tasks that have been chosen. A study’s design is only as good as the tasks that have been chosen. There should be as few explanations for your resulting data as possible. There should be as few explanations for your resulting data as possible. If a result is surprising, look back to your task. If a result is surprising, look back to your task. http://www.wilderdom.com/personality/L3- 2EssentialsGoodPsychologicalTest.html#Validity http://www.wilderdom.com/personality/L3- 2EssentialsGoodPsychologicalTest.html#Validity

13. Over to Tom…