Millisecond Forums

Hello to all!

I have written a script for an attentional bias (visual probe) task. The participant is simultaneously shown two pictures, one food related and one neutral control. Then a probe will appear (an arrow) and their task is to indicate whether the arrow is pointing upwards or downwards. 

There are 128 trials and 16 unique trial types, each presented eight times. The 16 trial types are based upon the following 2x2x2x2 parameters: probe left/right, probe up/down, food picture high calorie/low calorie and probe behind the food picture/neutral control. Trials are presented randomly. I have 16 pairs of stimuli that are presented eight times across the experiment.

The question: I would like to amend my script so that each of the pair of stimuli is presented in each of the 16 trail types one time. At the moment each trial type is presented eight times, and each stimuli pair is presented eight times...but if I look at my data file, the file type7 might have used only six of the eight stimuli pairs and used two of them twice.

Here are excerpts from my script so you can see what I have done...

************************high_cal left up********
<trial 1>
/ validresponse = ("t", "v")
/ correctresponse = ("t")
/ inputdevice = keyboard
/ stimulustimes= [1 = fixation; 501 = blank; 502= high_cal_left, high_neu_right;  1002 = blank ; 1003 = probe1left]
/ timeout = 2500
</trial>

<block 3>
/ preinstructions = (maintask)
/ trials = [1-128 = random | noreplace (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16)]
</block>

Is there any way of making each stimuli appear only once in each trial type!? Any help would be very much appreciated!!! I will even write out all 128 trial combinations manually if I have to! (I'm just not sure how to do that).

Thanks in advance for all your help,
Jayne