[FieldTrip] equal number of trials across conditions

Stolk, A. a.stolk at fcdonders.ru.nl
Mon May 21 09:18:59 CEST 2012

Hi Vitoria,

With 'randperm' you can randomly select a number of trials from one set. If you think order is important, for example indicated by the the trialnumber, have a look at ft_stratify and method 'histogram'. 

I would perform these randomization steps after regular cleaning. Perhaps someone else has more fine-grained idea for your desired approach.


----- Oorspronkelijk bericht -----
> Van: "Vitória Magalhães Piai" <vitoria.piai at gmail.com>
> Aan: fieldtrip at donders.ru.nl
> Verzonden: Zondag 20 mei 2012 11:53:58
> Onderwerp: [FieldTrip] equal number of trials across conditions
> Hi everyone,
> I'm working on a dataset (ERPs, but this is not that relevant for the
> question, I believe) for which one condition elicited more errors than
> the other.
> I'd like to have both conditions with the same number of trials in the
> analyses.
> Ideally, I'd throw away the noisiest trials from one condition,
> instead
> of just start throwing away trials at random.
> I was thinking of using z-scores for that but I was wondering if any
> of
> you has already done this before and how. What would be the best way
> to go?
> Take the mean amplitude across all trials (collapsed over condition or
> not?) and calculate the z-score for each trial individually? Then take
> out the one with the largest scores? How does this approach sound?
> Does FT keep information about the variance for each trial somewhere
> in
> the output of an artefact rejection function? Or would I have to
> compute
> that myself?
> I'd appreciate any suggestions or feedback.
> Cheers, Vitória
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