different presentation times

[David McFarlane]

Jotapan,

>I only wan each word to appear once with the presentation time A or 
>B (and have this be chosen randomly although an equal number of 
>times during the experiment).

Aha.  Let me see if I have this now.  Let's say you have 10 different 
words.  You want a random selection of five of these to appear for 
2000ms, and the other five to appear for 5000ms.  Does that sound right?

For this you will need nested lists.  One way, let's use TrialList 
for the words, and DurationList for the durations.  Put each word in 
a row of TrialList, and put "DurationList" in the Nested 
column.  DurationList will have two rows, and a column for 
Duration.  Use 2000 for the Duration in one row, 5000 for the other 
row, and set Weight in both rows to 5 (i.e., half of 10, per our 
example above) .  Set all lists to Random selection (although, for 
practice, you shoud first run everything as Sequential to see how it 
works).  As an extra exercise, try setting the Weights in 
DurationList instead to 1 and see what happens.  Try other 
values.  Explore and learn.

BTW, you could just as easily reverse the roles of the word and 
duration lists.  I.e., let TrialList have two rows, and a column for 
duration, one row for each duration with a Weight of 5, and put 
WordList in the Nested column.  Then put your words in WordList, 
randomize everything, etc.  It's largely a matter of taste, or 
whatever you feel most transparently represents your problem domain.

-- David McFarlane, Professional Faultfinder


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