Creating blocks fulfilling multiple conditions simultaneously

[Muhammad Saad Yousuf]

Hi,

I am new to e-prime and am in the process of developing a project using it. 
As expected, I have run into a few problems which will be told later after 
I explain the experiment.

In essence, the experiment is quite simple and much easier than quite a few 
that I have read in previous posts. There are four different conditions: 
Same object same size (SOSS), same object different size (SODS), different 
object different size (DODS), and different object same size (DOSS). Also, 
across these conditions, there are four different objects: A, B, C, and D. 
For each object category there are 6 exemplars. The paradigm is a simple 
one-back task indicating if the two objects in the trial are same or not 
(Fixation --> Object 1 --> Mask --> object 2 --> mask --> response). Each 
block should contain 24 trials that have equal number of objects varying 
across the conditions. That is to say that each trial must have all four 
conditions but use equal amounts of objects within these conditions to 
fulfill that requirement. The sequence of presentation must all be 
randomized and counterbalanced.

For example, block 1 may have the following sequence depicting different 
conditions:

A (SOSS)
C (SODS)
D (SOSS)
B (DOSS)
D (DODS)
C (DOSS)
B (SODS)
A (DODS)

There would be three blocks like this one in a given set with randomized 
stimuli without repeats (total of 24 trials) and four different sets for a 
complete total of 96 trials. As you can see, each object within its 
respective condition only occurs once across the blocks. In total there are 
2 of each conditions and 2 of each objects but the combination of each 
occurs only once. 

When I try to program this in e-prime, I could randomize the selection of 
each object with their respective conditions and limit it to choosing only 
2 samples. However, I cannot ensure that across the 3 blocks the same 
object from the same condition does not show up. I know there must be 
someway to accomplish this in e-prime...only if knew :(

I hope the above makes sense....

Thanks for all your help.

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