Manipulating validity and SOA in cueing task - not working

Shahd
Guest

Manipulating validity and SOA in cueing task - not working Oct 16, 2019 23:15:35 GMT

Quote

Post by Shahd on Oct 16, 2019 23:15:35 GMT

Hi all,

I've made some modifications to the exo/endo task, but I've kept the structure of validity similar. In my task, there are 200 trials. I'd like 60% of them to be valid, whilst the remainder are invalid. In keeping with the example, I've written:

## choose valid/invalid

set $valid random from 1 1 1 0 0 ## this means 40% invalid; valid=1,invalid=0

    if $valid == 1 # if valid, cue and target are the same

        set $cue random 1 4

        set $target $cue

    fi

if $valid == 0 # if not valid, cue and target must be different

    set $cue random 1 4

    set $target random 1 4

        while $cue == $target #if cue and target still the same then randomise target until they're not

            set $target random 1 4

        while-end

fi

However, when I run the task, I do not get 40 invalid trials. At times I get 38. At times I get 36. It's unclear to me the reason this may be happening. Any help would be appreciated.

Moreover, I'd like to have a random SOA of either 500 or 1000. But, I'd like an equal number of each SOA presented within each validity condition (i.e., 30 valid trials will be SOA 500 and 30 will be SOA 1000). Can such a rule be implemented? I had the below to start off:

set $SOA random from 1 0 #variable SOA to make target appearance random from 1 = 500 to 0 = 1000

if $SOA == 1

readkey 1 500 # wait and ensure no key has been pressed

fi

if $SOA == 0

readkey 1 1000 # wait and ensure no key has been pressed for 1000ms before presenting target

fi

But, again, that doesn't ensure equal presentation of each SOA overall, let alone within each condition of validity.

PsyToolkit
Administrator

Posts: 547

Manipulating validity and SOA in cueing task - not working Oct 17, 2019 10:07:48 GMT

Quote

Post by PsyToolkit on Oct 17, 2019 10:07:48 GMT

There are 2 questions here, which I will answer separately....

1) How do I get exactly the same numbers of trials as requested. Now in your case, there is a random selection, so you will get something close.

If you want instead EXACTLY the numbers do it as follows:

- Make one "task" for valid trials (for example valid_task)

- Make one "task" for invalid trials (for example invalid_task)

Then in your "block" create a task list as follows with trial numbers behind the tasks matching your likelihood. For example

tasklist

valid_task 60

invalid task 40

end

2) Again, you want EXACTLY the numbers you want. That means you do not have pure randomness, and that can be done, similarly to the solution to question 1.

Of course, if you are really so detailed about the exact numbers, you need to ask yourself some other questions as well: For example, what happens when people make a mistake.

It maybe that a participant just looked out of the window for two seconds and missed a trial. Is that not a problem for you? If not, then why do you want to enforce exact trial numbers

instead of a real randomness. Of course, I know, some people want to do it that way, it is technically possible, but not really making any difference, I think.

If you want to have more control, you can also do the following, as a completely different solution:

- Make one task, and let valid/invalid as well as SOAs set by the table

- Make a large table, do the randomization "offline" and include that table.

- Run the table with the "fixed" option as follows:

tasklist

my_task fixed 100

end

Shahd Guest	Manipulating validity and SOA in cueing task - not working Oct 22, 2019 4:01:48 GMT Quote Select Post Deselect Post Link to Post Back to Top Post by Shahd on Oct 22, 2019 4:01:48 GMT Thanks; the first suggestion worked and was easy to implement. Cheers, Shahd

Manipulating validity and SOA in cueing task - not working

Post by Shahd on Oct 16, 2019 23:15:35 GMT

Post by PsyToolkit on Oct 17, 2019 10:07:48 GMT

Post by Shahd on Oct 22, 2019 4:01:48 GMT