critical timing (working with prerelease and event timing)

[Jim]

Hello forum,

I sent this question to e-prime support last week; unfortunately, they
are experiencing high volume and have been taking a long time to get
back to my requests. They are time sensitive, so I was hoping the
forum might have some ideas.

I was sent an e-prime task, and I will be using it in conjunction with
a physiological data collection system. I have figured out how to send
TTL pulses from e-prime to the physio system, and have the physio data
collection starting with a pulse from each block of the task. However,
there is no way to offset the physio data collection with a pulse, so
the offset of the physio data collection is specified by a user-
defined duration.

The problem I am running into is that each block of my task does not
end at the same time each time I run it. After reading the critical
timing chapter of the e-prime manual, I understand now why this is the
case (at least in part). However, I am not sure how to fix this
problem for my particular task. Presently there is no prerelease
specified and all objects are set to event timing mode; I have
questions about both of these options as they relate to this specific
task:

Prerelease: The task consists of several blocks, and within each block
is a repeating sequence of events; a stimulus is shown for 3 seconds,
the participant responds during that interval and is given on screen
feedback as an overlay on the stimulus screen (the latency of the
feedback presentation is contingent upon participants' response;
regardless of participants' response the stimulus is displayed for 3
seconds), then there is a 500ms blank screen. After reading the
critical timing chapter, I got the impression that one should not use
prerelease on sequences including feedback. I get the sense that I may
be able to have prerelease on some objects but not others, but it is
very important that the data logging and feedback are correct for the
task, so I am reluctant to use prerelease on anything. Thoughts?

Event timing: Although I understand the difference between cumulative
and event timing, I am still having a hard time grasping the
implications of using each for my experiment; in particular I am not
sure how each choice would impact data analysis. E-prime will be
sending pulses to the physio machine that onset and offset with the
onset and offset of each stimulus. I want to be able to look at
physiological response to the stimuli (so it's an "event-related"
design). Given my question, I'm not sure about the relative pros and
cons of event and cumulative timing and what impact that decision will
have on my attempts to analyze the data. I am reluctant to change it
to cumulative timing because the task was made with "event timing"
set. Again, it seems like here too it might be best to use event
timing on certain objects and cumulative timing on others, but I'm not
sure what impact this would actually have on the experiment or which
objects to use what timing on.

Thank you so much for your help
Jim

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