Experimental design

Optimizing event design patterns

The distribution of inter-stimuli interval (ISI) durations is a crucial issue in order to optimize event protocols.

In this regard, we advice to consult Rick Henson‘s pages on the efficiency of experimental designs in fMRI.

Design efficiency in FMRI

Matthew Brett wrote a Matlab routine to generate exponential distributions of ISI.

We used his routine to write a function to generate – for N desired runs – an exponential distribution of IIS.

Two annotated .m files are provided :

ISIGeneration.m : The function that generates the ISI distribution.
MakeTiming.m : The code that uses ISIGeneration.m

MakeTiming.m will generate N runs with only the inter-stimuli intervals (correctly randomized). It does not include the stimulus durations. Moreover, the N runs will have the same length in time, expressed in number of MRI-slices.

The code is annotated and can be easily modified in order to set the number of runs, the minimum duration, the average ISI duration, the duration of an MRI-slice, …