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LINGUIST List 16.2104

Thu Jul 07 2005

Sum: Stimulus Presentation Packages

Editor for this issue: Jessica Boynton <jessicalinguistlist.org>

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        1.    Michael Ullman, Stimulus Presentation Packages

Message 1: Stimulus Presentation Packages
Date: 06-Jul-2005
From: Michael Ullman <michaelgeorgetown.edu>
Subject: Stimulus Presentation Packages

Regarding query: http://www.linguistlist.org/issues/16/16-1805.html#1

A few weeks ago we asked about stimulus presentation packages.

Here's the summary of responses.

Two people reported positive experiences with E-Prime, one with DMDX.
SuperLab, DirectRT, and PsyScope were all recommended as possible
alternative packages.

Nobody warned us away from any of the software.

We also asked a few specific questions about response boxes, voice
triggers, and how to deal with the inherently imprecise display timing of
LCD monitors. A few people provided more detail in their responses:

One respondent said that E-Prime's proprietary response box is very easy to
set up and use with voice or button-press input. The consensus is that
it's not possible to use any other voice-trigger hardware with E-Prime
unless you're willing to accept timing inconsistencies or have the aid of an
electronics lab.

Another writer told us that E-Prime's timing is rumored to be poor, but
that if so it would probably be improved in the upcoming E-Prime 2.0. He
suggests an empirical test of display timing using "a photocell and
netstation software (with a precision to ~15 ms). We compare this with how
long e-prime states it is displaying the stimuli and adjust accordingly."
A coarser test would be to run many stimuli in succession and time them
with a stopwatch, to make sure there's no cumulative drift in the timing.

It was also noted that E-Prime's tech support generally takes 2-3 days to
respond, regardless of whether the question is simple or difficult; all
tech support is via e-mail.

Another respondent had very positive experiences with DMDX. His advice is
worth quoting at length: "For what it's worth, I've used DMDX with voice RT
triggering (and also recording of the responses) very succesfully, thanks
to the easy adjustment of level that is offered in the user interface that runs
the experiment. It did take a while to figure out how to set up everything
properly, and resposes from the user group mailing list were extremely heplful
in that. Since the level adjustment gives a complete picture of the triggering
behavior, the experimenter can easily check if the result meets with
requirements before running each person. As with any voice triggering system,
the most important thing is the signal to noise ratio: if the environment is
noisy (or the microphone too low gain, or the audio card too noisy) then voice
triggering will not work well. Also, microphone placement, and probably
microphone cover angle are likely to affect the triggering quite substantially.
I don't think the audio card per se is a major aspect as long as it is not
excessively noisy; in fact a relatively high-quality yet simple AC'97 internal
laptop audio card (on an IBM T40) has given me excellent results.

DMDX also has the advantage of very strictly controlled (and measured)
adherence to refresh timing, and fMRI-related triggering. I haven't tried
to verify their claims about accuracy but the TimeDX suite of tests
supplied with DMDX at least indicates that timing has been taken extremely
seriously in the development of this package."

He also has recommendations for synchronizing audio and visual stimuli:

"If it is important to synchronize audio to visual presentation down to
within less than 10 ms or so (25 ms on-off time is typical but there are
much faster LCD monitors around these days), I would recommend using a
two-channel oscilloscope with a simple (and very fast) photosensor and the
audio output on the other channel (after ensuring from TimeDX that the
audio loop delay is within acceptable limits). The precise on/off curves
and associated time delays, for the screen region and pixel values of
interest, at the desired luminance and contrast settings, can then be taken
into account in setting up the frame sequence for programming DMDX (a task
which, by the way, is quite simple in DMDX, thanks to the frame-based
design of the entire trial setup)."

Many thanks to everyone who replied!


Michael Ullman
Chris Maloof

Brain and Language Laboratory (http://brainlang.georgetown.edu)
Georgetown University

Linguistic Field(s): Neurolinguistics

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