ordering trials

Hey im trying to work out what method to use to order my image sequences

I have 2 images displayed on the screen at any one time and the user has respond or image time out after 240ms

the problem is i have 4 folders of images call them a,b,c and d folders
i have txt lists of all images in these directories ie picA.txt picB.txt picC.txt and picD.txt

the images themselves can never be the same image if drawn from the same imageset
the valid orders are of the two images displayed at any time are as below
A,A
B,B
C,C
D,D
A,C or C,A
A,B or B,A
A,D or D,A
C,B or B,C

what method to organise these groups would work best?
as i said above i have image lists for each of the 4 folders at the moment and i can display the images and make sure there only displayed once each and never repeated. im just not sure how to randomly pick between entire different groups of stimuli
thanks for any help
richard

A couple ways off the top of my head--create the trials in such a way that you explicitly call the stimuli from the different groups, and then randomize the order of those trials using WGR values. This will give you a fixed number of each group combination.

Or for a truly random alternative---for any given trial, you could create 12 identical versions where only the groups of stimuli differ. Then assign the same WGR value to each of those 12 trials so that the first one presented will be randomly determined. Then, no matter which of the 12 trials occurs first, have it skip over the remaining 11 to the next.

Any of that make sense?

it does make sense i guess but more specifically say i have 70 images in each of the 4 directories would i need 280 entries in my excel table? or is there a way to do a loop in directrt so you can say keep displaying random images from this text file until some limit is exceeded

No way to loop yet, but it's on the to-do list for the next version.