Dear SPMers,

 I am attempting to specify a model using parametric modulation in
SPM99.  Unfortunately, I’ve been running into several roadblocks.  First,
let me describe the design, and then I’ll describe the problems.
 For each subject there are 5 runs, each run having 114 scans and a
TR=2.5.  The conditions are replicated in each run, but the timing
parameters vary by run as a function of the parametric modulation.  There
are three conditions: rest, lexical decision, and property generation.  In
all runs the onset vectors are as follows:
     Rest = 1, 97
     Lexical decision = 15, 43, 71
     Property Generation = 29, 57, 85
The parametric modulation pertains to the property generation condition.
There are three types of words about which subjects should generate
properties: low word associate words, medium word associate words, and high
word associate words.  The order in which the three word associate levels
are presented is counterbalanced across runs.  For example, on some runs
the low word associate condition appears at scan 29, on others it might
appear at scan 85, and so on for each word associate level.

This now brings me to my problems.
1)  When I enter Rest as the first condition, lexical decision as the
second condition, and property generation as the third condition, SPM
crashes on me as soon as it asks “which trials” the parametric modulation
variable should pertain to.  The input of events looks something like the
following:
  - Vector of onsets for Rest = 1 97
  - Variable durations = no
  - Vector of onsets for LexicalDecision = 15 43 71
  - Variable durations = no
  - Vector of onsets for PropertyGeneration = 29 57 85
  - Variable durations = no
  - Parametric modulations = other
  - Name of parameter =  WA_level
  - Expansion =  linear
  - Which Trials =  3
At this point all of SPM freezes.  When I look in the Matlab window I see
the following error messages:

     SPM99: spm_fmri_design (v2.27)             11:46:41 - 23/09/2003
     ----------------------------------------------------------------
     ??? Index exceeds matrix dimensions.

     Error in ==> C:\matlab_sv12\spm99\spm_get_ons.m
     On line 399  ==>                 ns    = length(on{i});

     Error in ==> C:\matlab_sv12\spm99\spm_fMRI_design.m
     On line 215  ==>   [SF,Cname,Pv,Pname,DSstr] = ...

     Error in ==> C:\matlab_sv12\spm99\spm_fmri_spm_ui.m
     On line 206  ==>  [xX,Sess] = spm_fMRI_design;

     ??? Error while evaluating uicontrol Callback.
     ----------------------------------------------------------------

     I’ve downloaded all the most recent patches and this doesn’t seem to
fix anything.  Any ideas about how to fix this?

2)  As a work-around for this problem I tried to enter all three conditions
into the design, but this time entering the property generation condition
as the first condition, with lexical decision and rest being the second and
third conditions.  In this case, I am able to get past the previously
described error, but a new error arises.  Now, when it asks for the
parameters for the property generation variable (i.e., the onset vectors
indexing the low, medium, and high word associate blocks), it will only
allow me to enter 2 vectors, rather than the three that I need to enter.
In this case, the input of events looks like the following:
  - Vector of onsets for PropertyGeneration = 29 57 85
  - Variable durations = no
  - Vector of onsets for lexdec = 15 43 71
  - Variable durations = no
  - Vector of onsets for rest = 1 97
  - Variable durations = no
  - Parametric modulations = other
  - Name of parameter =  WA_level
  - Expansion =  linear
  - Which Trials =  1
  - [2] Parameters for PropertyGeneration =
When I try to enter 57 29 85 (which shows that the low word associate came
at scan 57, medium at 29, and high and 85) I get an error saying “2
vector required”.  Any suggestions why this might be the case?

Thanks,
 Kyle