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Continuous Performance Task Implementation

Hi guys,

I’m trying to create a Continuous Performance Task, much like the IVA. In this task, numbers 1 or 2 appear either on the screen as an image or they are played as auditory stimuli. Participants should respond whenever they see or hear the number “1”. (it’s important that only one stimuli is presented at any given time)
I have a couple of problems implementing this task:

1- The stimuli should be image or audio. Since I can’t put both kinds of stimuli in one condition file, Is it possible to suppress playing one kind of stimuli in a loop while the other one is being presented? (my solution thus far is to present both of them as movie files!)

2- During some parts of the task, the target stimuli (number one) should be presented more often, but they still have to be presented randomly. Since there are roughly 500 trials, I don’t think that it’s very efficient to create a conditions file this long and loop through it sequentially. Is there some better way to indicate a percentage for presenting one of the conditions in the loop? (i.e. 80% of the stimuli have to be something specific, and the other 20% can be presented randomly)

Since I’d like to use the export HTML option and run the experiment online, I prefer to build the experiment using the builder. But if there are any solutions which would require coding please do not hesitate to share them, I can probably manage to convert the python code to JavaScript.