critical timing (working with prerelease and event timing)

[David McFarlane]

Jim,

Please see my comments in your thread, "scoring a nonresponse as a 
correct answer".

(OK, now I'm late for my yoga class, and I really need the exercise.)

-- David McFarlane, Professional Faultfinder


>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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