I'm reading an unusual implementation of the partial/catch trial design that's used to separate out two trial components which occur in a fixed sequence (a la Ollinger) -- my question is about whether this method is better/worse than the standard way.
Normally one would have two versions of a trial, the "whole trial", for example a cued anticipation period "A" for 6 seconds (where the subject is cued about whether an upcoming picture is going to be negative or neutral) always followed immediately by a picture event "B" (6 s.) and then a variable ITI (say, 4-7 s.). The "partial trial" would be the same as this sequence except that the second event (B) would be omitted (on about 30% of trials). The goal is to separately estimate responses to affective picture anticipation vs. responses to affective pictures.
I'm reading a study in which the authors include an additional type of partial trial, namely, just the second event (and the ITI of course). Does anyone have some suggestions as to why a second type of partial trial would be desired? The estimation of both component events should work out fine with just one type of partial trial, so I don't quite understand the need for a second type of partial trial (it isn't explained in the paper).
-- Stephan
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