Variable stimuli duration for PPI analyses


I am currently working on running a PPI analyses with a task (The Virtual School Task) that has variable stimuli duration and stimuli that directly abut each other (i.e. there is no ITI between stimuli) . When setting up the portion, how can I account for the variable stimuli duration and make sure that stimuli labels do not get added twice or incorrectly for bins that are created that make encompass part of on stimuli and part of another stimuli (since they are right next to each other in time) and there is a variable duration for each stimuli? Is it possible to use the stimuli onset-duration married files for the or do they need to be onset only?

Here is the code i have for the, but again i am concerned that even having the min_frac at 51% that there will be issues with stimuli labeling.

   echo "== running to create per-run timing files"
foreach cond ( $cond_list ) -timing $stimonsetdir/${cond}_Onset.txt -tr 0.1   \
		       -min_frac 0.51 -run_len 502 -tr 2.0 		\
		       -timing_to_1D 00a.${sub}.${cond}.upsam -per_run_file

	# first output file might have name: 00a.$subj.$cond.upsam_r$run.1D


Sorry, it looks like I did not reference this anywhere in the help.

If the timing files are duration modulated (form ONSET:DUR for each event), then the program will apply those durations.

You can test it using something like example 13a, to show the events, durations and offsets (time between events = ITIs): -multi_timing stim.* -multi_timing_to_event_list GE:ALL -

If there is no :DUR modulation attached, then you should specify the duration on the command line.

The special case comes (with the same example 13a, say) when some timing files have duration modulators and some don’t. In that case, it would be necessary to specify the fixed times via -multi_stim_dur. But since you would not want to override the :DUR entries, -multi_stim_dur should get -1 for any class that has modulators.

That is more than you asked about, but hopefully it clarifies things.

  • rick