Millisecond Forums

> Everything is running and saving beautifully, but I'm not having an equal number of video-audio stim pairings. [...]

There is no reason you should get equal pairings. Nowhere in your script do you define any such pairings.

All your video items (pleasant, unpleasant, neutral) are in a single element and are sampled randomly without replacement:

<video videoclip>
/ items = VideoClipList
/ select = clip.counter
/ size = (50%, 50%)
/ position = (50%, 50%)
</video>

<counter clip.counter>
/ select = noreplacenorepeat (1-27)
/ resetinterval = 0
</counter>

<item VideoClipList>
/ 1 = "basejump_pleasant.mp4"
/ 2 = "beach_pleasant.mp4"
/ 3 = "biking_pleasant.mp4"
/ 4 = "canyon_pleasant.mp4"
/ 5 = "field_pleasant.mp4"
/ 6 = "penguins_pleasant.mp4"
/ 7 = "puppy_pleasant.mp4"
/ 8 = "waterfall_pleasant.mp4"
/ 9 = "flysuit_pleasant.mp4"
/ 10 = "car_neutral.mp4"
/ 11 = "city_neutral.mp4"
/ 12 = "clothes_neutral.mp4"
/ 13 = "digging_neutral.mp4"
/ 14 = "home_neutral.mp4"
/ 15 = "photocopier_neutral.mp4"
/ 16 = "typing_neutral.mp4"
/ 17 = "windfarm_neutral.mp4"
/ 18 = "planes_neutral.mp4"
/ 19 = "Hiroshima_unpleasant.mp4"
/ 20 = "holocaust_unpleasant.mp4"
/ 21 = "pigs_unpleasant.mp4"
/ 22 = "pollutedriver_unpleasant.mp4"
/ 23 = "snakes_unpleasant.mp4"
/ 24 = "surgery_unpleasant.mp4"
/ 25 = "tumor_unpleasant.mp4"
/ 26 = "watermelon_unpleasant.mp4"
/ 27 = "dogpoop_unpleasant.mp4"
</item>


All your trial elements display that single video element:

<trial repeated.videos>
/ stimulustimes = [0 = videoclip; 10000= audioinstruction.repeated1; 30000 = audioinstruction.repeated2]
/ validresponse = (anyresponse)
/ timeout = 40000
/ posttrialpause = 1000
</trial>

<trial nonrepeated.videos>
/ stimulustimes = [0 = videoclip; 10000 = audioinstruction.nonrepeated1; 30000 = audioinstruction.nonrepeated2]
/ validresponse = (anyresponse)
/ timeout = 40000
/ posttrialpause = 1000
</trial>

<trial viewing.videos>
/ stimulustimes = [0 = videoclip, audioinstruction.viewing]
/ validresponse = (anyresponse)
/ timeout = 40000
/ posttrialpause = 1000
</trial>

Over the course of the experiment, each of the above trials will be run 9 times. However, there is no reason whatsoever why e.g. <trial viewing.videos> should sample exactly 3 unpleasant videos, 3 pleasant videos and 3 neutral videos across those 9 runs.

If you have a shuffled deck of 4 black cards and 4 red cards and then proceed to draw 4 cards with your left hand and 4 cards with your right, there is no reason why you should end up with exactly 2 black cards and 2 red cards in your left hand (same for your right hand). That's precisely the issue here.

To fix the above, you need to add an additional layer of selection. I.e., make sure that each of the <trial>s mentioned above gets exactly 3 pleasant, 3 neutral and 3 unpleasant videos across its 9 runs. This can be accomplished using a bunch of <list> elements and some bits of conditional logic /ontrialbegin. See the attached file for details (look for "*** NEW STUFF ***").