Bob,

OK. I think I may have figured it out. The problem seems to be that my columns in any given 1D do not all have the same number of rows. This is a result of subject response-driven trial types. waver (or 1dcat) then only uses the number of rows specified in the shortest column. So, in my original example, only the first row was used, but in another subject, the first 4 rows were used.

I tired to fool waver by adding 0's at the end of the short columns so they all had the same length. Unfortunately, this produced a hemodynamic response at Time = 0, which is never the case in reality (guess that's what I get for trying to fool a Klingon program).

So, unless you have any other suggestions, it looks like I am stuck with making 4 separate files, instead of 1 file with 4 columns.

As always, thanks for your help.

Sean