stimulus presentation packages

[Michael Ullman]

A few weeks ago we asked about stimulus presentation packages.
Here's the summary of responses.

We asked, "We're considering E-Prime (Psychology Software Tools), 
Presentation (Neurobehavioral Systems), and DMDX (a free package from 
the University of Arizona).  Any specific/general concerns or 
positive comments about these would be greatly appreciated."

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!

Best,

Michael Ullman
Chris Maloof

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