rapid presentation event related design for fmri n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Rapid-Presentation Event-Related Design for fMRI PowerPoint Presentation
Download Presentation
Rapid-Presentation Event-Related Design for fMRI

Loading in 2 Seconds...

play fullscreen
1 / 17

Rapid-Presentation Event-Related Design for fMRI - PowerPoint PPT Presentation


  • 532 Views
  • Uploaded on

Rapid-Presentation Event-Related Design for fMRI. Douglas N. Greve. Outline. What is Event-Related Design? Fixed-Interval Event-Related Rapid-Presentation (Jittered) Event-Related Efficiency and Event Scheduling Mathematical Basis optseq – a tool for RPER design

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Rapid-Presentation Event-Related Design for fMRI' - brencis


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide2

Outline

  • What is Event-Related Design?
  • Fixed-Interval Event-Related
  • Rapid-Presentation (Jittered) Event-Related
  • Efficiency and Event Scheduling
  • Mathematical Basis
  • optseq – a tool for RPER design
  • (http://surfer.nmr.mgh.harvard.edu/optseq)

Rapid-Presenation Event-related Design for fMRI -- Douglas N. Greve

dispersion
Dispersion
  • Dispersion is the spreading out of the response over time, usually far beyond the end of the stimulus
  • How closely can one event follow another?

Rapid-Presenation Event-related Design for fMRI -- Douglas N. Greve

event related fmri
Event-Related fMRI
  • Estimate response from a single event type
  • cf Blocked Design (Habituation, Expectation, Set, Power)
  • Randomize Schedule (Order and Timing)
  • Post-Hoc Event Sorting
  • Multimodal Integration (EEG/MEG,Behavioral)
  • Fixed Interval and Rapid Presentation (Jittered/Stochastic)

Rapid-Presenation Event-related Design for fMRI -- Douglas N. Greve

event vs event type
Event vs Event Type
  • Three Event Types (yellow, red, green)
  • Number of Events (Repetitions) per Event Type
    • Yellow: 2
    • Red: 2
    • Green: 3
  • Two events belong to the same Event Type if, by hypothesis, they have the same response (violations are treated as noise).
  • Event Type = Condition = Trial Type = Explanatory Variable
  • Event = Stimulus = Trial

Rapid-Presenation Event-related Design for fMRI -- Douglas N. Greve

event schedule
Event Schedule
  • Description of which event is presented when

time code duration label

4.0 2 4 yellow

20.0 1 2 red

36.0 1 2 red

52.0 3 6 green

  • Time is the accumulated time since onset of scanning run
  • Code unique numeric id
  • Output of optseq

Rapid-Presenation Event-related Design for fMRI -- Douglas N. Greve

fixed interval event related

12-20s

Fixed-Interval Event-Related
  • Push trials apart enough to prevent overlap.
  • Interval fixed at minimum is most efficient.
  • Random Sequence (Counter-balanced)
  • Allows Post-Hoc Stimulus Definition
  • Mitigates Habituation, Expectation (?), and Set
  • Inflexible/Inefficient/Boring
  • Good if limited by number of stimuli (not scanning time)

Rapid-Presenation Event-related Design for fMRI -- Douglas N. Greve

rapid presentation event related
Rapid-Presentation Event-Related
  • Closely Spaced Trials (Overlap!)
  • Raw signal uninterpretable
  • Random Sequence and Schedule
  • Highly resistant to habituation, set, and expectation
  • Jitter = “Random” Inter-Stimulus Interval (ISI/SOA)

Rapid-Presenation Event-related Design for fMRI -- Douglas N. Greve

scheduling and efficiency

A: N=5

B: N=10

Scheduling and Efficiency

C: N=10

  • Efficiency is statistical power/SNR/CNR per acquisition
  • Efficiency increases with N (number of observations)
  • Efficiency decreases with overlap
  • Efficiency increases with differential overlap
  • Choose schedule with optimum efficiency before scanning

Rapid-Presenation Event-related Design for fMRI -- Douglas N. Greve

mathematical concepts
Mathematical Concepts

Forward Model

(X = design matrix)

Inverse Model

Residual Error

Rapid-Presenation Event-related Design for fMRI -- Douglas N. Greve

slide11

Contrast, Contrast Vector

(or Matrix), Contrast Effect Size, COPE (FSL)

t-Ratio

Efficiency

Variance Reduction Factor

Rapid-Presenation Event-related Design for fMRI -- Douglas N. Greve

where does jitter come from what s a null condition
Where does jitter come from?(What’s a Null Condition?)
  • “Null” condition – fixation cross or dot
  • By hypothesis, no response to null
  • Insert random amounts of null between task conditions
  • Differential ISI = Differential Overlap

A

+

B

A

+

A

B

A

+

+

B

+

B

A

Time

Rapid-Presenation Event-related Design for fMRI -- Douglas N. Greve

design parameters optseq
Design Parameters (optseq)
  • TR – time between volume acquisition (temporal resolution).
  • Ntp – number of time points (TRs, frames, volumes, …)
  • Nc – number of event types (conditions)
  • Npc – number of events/repetitions of each event type (can vary across event types)
  • Tpc – duration of each event type (can vary across event types)
  • Schedule – event onset time and identity
  • Event Response Model – FIR Post-Stimulus Delay Window (needed for optimization)

Rapid-Presenation Event-related Design for fMRI -- Douglas N. Greve

time constraints
Time Constraints

Total Scan Time = Ntp * TR

A

B

C

+

Null Time

Ta = Na*Tpa

Tb = Nb*Tpb

Tc = Nc*Tpc

Total Stimulation Time

  • Total Stimulation Time Cannot Exceed Total Scan Time
  • How much Null Time is needed? Rule of thumb: same as any other task condition (or the average of the task conditions).

Rapid-Presenation Event-related Design for fMRI -- Douglas N. Greve

event response model fir

PSDMin

PSD=0

PSDMax

dPSD

Event Response Model (FIR)
  • PSD: Post-Stimulus Delay (PSD = 0 = Stimulus Onset)
  • PSDMin: Response is zero for PSD < PSDMin
  • PSDMax: Response is zero for PSD > PSDMax
  • PSD Window should be long enough to capture response
  • Response can be anything in between (FIR model)
  • dPSD: sets basic temporal resolution for schedule
  • DOF Constraint: Nbeta = nPSD*Nc < Ntp

Rapid-Presenation Event-related Design for fMRI -- Douglas N. Greve

other optseq parameters options
Other optseq Parameters/Options
  • Getting help: optseq2 --help
  • Search termination criteria: nsearch/tsearch
  • Output files (and format)
  • Optimizing over number of repetitions
  • Nuisance variables (polynomial drift terms)
  • Cost Functions
  • First-Order Counter-Balancing Pre-optimization
  • http://surfer.nmr.mgh.harvard.edu/optseq
  • To come: contrasts and non-FIR

Rapid-Presenation Event-related Design for fMRI -- Douglas N. Greve

rapid presentation properties
Rapid-Presentation Properties
  • Efficient (not as efficient as blocked)
  • Can distinguish responses despite overlap
  • Highly resistant to habituation, set, and expectation
  • Flexible timing (Behavioral, EEG, MEG)
  • Linear overlap assumption
  • Analysis: Selective Averaging/Deconvolution (GLM)
  • Schedule Optimization Tool (optseq)

Rapid-Presenation Event-related Design for fMRI -- Douglas N. Greve