Hello Dave, 
Thank you for your previous post about how to change the number of trials. 
Now that I successfully have the amount of trials (yay!), I am finding that some of the picture pairs are presented 6 times, and some are presented 2 times, whereas each picture pair should be presented 4 times. I understand this is probably to do with how I have edited the item_numbers list:
Orignially, it had:
Alcohol_target_itemnumbers
/ items = (
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

Filler_target_itemnumbers
/ items = (
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

Basically, meaning there will be 40 critical, and 40 control trials, resulting in 80 total. 

When I edited it for my own task, I need 160 trials instead of 80, so I simply edited the lists as follows:
Alcohol_target_itemnumbers
/ items = (
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
Filler_target_itemnumbers
/ items = (
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)

Essentially, this should result in each picture pair being presented 4 times. But for some reason, when I (painfully) counted each picture pair, some were presented only once, some were presented twice, some three times, some 4 times, some 5 times... up to 7 times for some. I am not sure why this is the case, when all i have done is doubled what was initially there. 

ALSO!
Since changing the 
/ trials = [1-80] to
/ trials = [1-160],
The probe is now only on the left?? Through the whole task! 

Man, I am feeling really useless at the moment, and any suggestions you have are most welcome!

Thanks in advance, 
stefania 

I have tried to delete this post (don't know how) as i have found the error of my ways! It is now fixed. Apologies!

I'm glad you were able to find the error and I can delete this thread if you want to, just let me know. One remark for any future similar queries, though, if I may: While including some code excerpts highlighting some of the things you changed is very useful, I will usually also need the actual full script as well as all external files (images, etc.) the script needs to run to diagnose a given problem and/or find and fix any mistakes. Please put these things in a ZIP file and then you can attach that to your post by clicking +Insert -> Add File...



Thanks!