Controlling for Frequency of Trial Types Following Given Trial Types

[Olivier Hart-Vilain]

Hello, I am coding a flanker task and want to ensure that there is a fixed ratio of each of four trial types (incongruent left, incongruent right, congruent left, congruent right) following each other. Is there a feature in Eprime that would allow for this to be done? I am using variables in a trial list to dictate the flanking and target arrows.

Thanks for any help ahead of time!

[Michiel Spape]

Hi,

Well, if you’re into trial-by-trial effects, the way I went about this (Spapé & Hommel, 2008) is by just programming the sequence within the same trial procedure, so you have

S1: [stimulus1]

Response (maybe FB)

S2: [stimulus2]

Response (maybe FB)

Then next trial.

 

So you get to put into the same list

Stimulus1            Stimulus2

LLLLL                      LLLLL

LLLLL                      LLRLL

LLLLL                      RRLRR

LLLLL                      RRRRR

LLRLL                     LLLLL

LLRLL                     LLRLL

LLRLL                     RRLRR

LLRLL                     RRRRR

…and so on. Randomise across 16 possibilities.

 

Of course, this doesn’t quite balance the S2->S3 frequencies, but since S1->S2 IS balanced, you’ll find a much better balance across trial types overall. Alternatively, crunch the math with python/MATLAB and just load a list prior to each participant.

Best,

Michiel

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