selecting stimuli without replacement from a list, but using the same stimuli consistently on trials within a block

[Katie S]

Hi all

Here is my situation:

I want to present shapes paired with sounds, first shape, then sound,
in three different blocks.

In each block, there are 16 shape-sound trials: 12 common sounds and 4
oddball sounds.

In one block, the same shape always predicts the same sound, so there
are 12 common shapes, 4 oddball shapes.
In another block, there is an "error" 25% of the time.  So there are 6
oddball shapes (3 before the the oddball sounds, 3 before the common
sound) and 10 common shapes (1 before the oddball shape, 9 before the
common shapes)
In a third block, it is random which shape predicts which sound, so
there are 6 of one shape before common sounds and 2 before oddball
sounds, and the same is true of the other.

I have some constraints I'd like to satisfy.  I'd like the oddball
sounds to be dispersed so that one occurs in each quarter of the 16
trials.  I probably have some others but I don't think that's
important for my current question.

I can write code just fine to generate two arrays that create a
constraint-satisfying pseudorandom order for my shapes and noises,
calling one arrShape and populating it with 1's and 2's, and the other
arrNoise and populating it with 1's and 2's.  I more or less already
have.

What I can't figure out: having specified that order, how do I assign
a shape to be 1, 2 and a noise to be 1,2, and where would I put the
order I generated to control the display of my shapes and noises?

If what I needed to do was select a random shape with a particular
characteristic on each trial, I would know how to do that with nested
lists.  But that's not what I need.  I need to select a shape randomly
from a list somewhere, designate it shape 1 (the same for sound 1,
shape 2, sound 2) and have that identity be consistent on each trial
through the block.  I also have some constraints about which two
shapes get paired together, so I need to be able to place some limits
on the selection of the second shape.  I need to generate the order
for the presentation of shape 1, sound 1, etc. (I already know how to
generate a constraint-satisfying pseudorandom order) , and use that
order to govern their presentation through the 16 trials. Then, those
shapes/sounds having been selected, I need them not to be used again
in subsequent blocks.

I am perfectly willing to code -- I just need some help with overall
approach, how to integrate code with the various E-Prime objects,
etc.  I would understand how to do this if it were a programming task
in a regular language -- what I don't understand is how to integrate
it in with the prefab E-Prime objects.

I would appreciate any help.

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