Stim timing adjustment in a continous loop

[Michiel Spape]

Hi,
You mean, you use a classical method of adjustment? I made an experiment, I think in 2001 or so, pretty much doing exactly what you want, but with A-B----C------------ rather than B----C, and written in Turbo Pascal. Pascal was already outdated, but still pretty new compared to psychophysiology itself :)
Anyway, 
1. YES, you can do that using E-Prime. But it won't be very easy, and probably easier in Pascal
2. YES, I did (see above).
3. Know that E-Prime isn't brilliant with audio (as I've remarked here before), and audio tones may get cut. This is precisely what would horrify anyone with some psychophysiological training, it certainly does to me. What you might and really should do is:
- Get syntrillium cooledit 2 (long out of date, called adobe audition nowadays, which is bloated - adobe-style - and doesn't offer much you'll find use for), or any wave-editing tool which offers millisecond time format for convenience. 
- Make ALL intervals, using generate tone and generate silence, like ----A----B--------, ---A------B--------, etc. Make sure to include a constant amount of silence before the first tone and after the second tone. Make sure both tones have a little envelope (fade in/out), to avoid clicks at the beginning and end of the tone. This may feel like an insane amount of work, but it's worth it, because A) you'll know your stimuli, B) you'll achieve 1 / 44.1 (about 0.02) ms timing accuracy (instead of 1 ms). Name them something like 50.wav, 100.wav etc, with each number being the timing. 
- Finally, in E-Prime, use a procedure like this:
1. short inline: 
	Dim currentinterval as integer  
	currentinterval = 1000 'base interval
2. Label1
3. next inline:
	c.SetAttrib "soundfilename", cstr(currentinterval) & ".wav"
4. SlideDisplay called SlideDisplay1 with duration = infinite, allowable response is {LEFT}{RIGHT}{ENTER}. On the SlideDisplay is placed a text with "Press left to make the interval shorter, right to make it longer, enter if satisfied" and a sound with filename [soundfilename]. 
5. Last inline (sorry for the lack of case, David):

	If SlideDisplay1.Resp = "{LEFT}" then 
		currentinterval = currentinterval - 50
		if currentinterval < 50 then currentinterval = 50 'to avoid 0 interval
		goto Label1
	else
	   if SlideDisplay1.RESP = "{RIGHT}" then 
		currentinterval = currentinterval + 50
		if currentinterval > 2000 then currentinterval = 2000 'to keep a boundary
	   end if
       end if

Variations, like your looping business can be easily extrapolated from this simple example.
That's it.
Cheers,
Mich

Michiel Spapé
Research Fellow
Perception & Action group
University of Nottingham
School of Psychology
www.cognitology.eu


-----Original Message-----
From: e-prime at googlegroups.com [mailto:e-prime at googlegroups.com] On Behalf Of Becky Prince
Sent: 09 February 2011 13:09
To: E-Prime
Subject: Stim timing adjustment in a continous loop

Dear Forum,

I have to create a task where participants hear two tones in a loop
and adjust the spacing between the tones (that is, they move the
second tone forward or backward in time) until the participant
perceives the tones to be rhythmic or isochronous.  We'd like to use
two keyboard keys as "+" and "-", which when pressed would move the
second tone forward or backward (say, 50ms) within the continous loop
of the two tones.

To illustrate, let's say the tones are "A" and "B", and the dashes
represent some unit of time:
A---B-----------A---B-----------A---B-----------
The duration of the loop (from onset of A to onset of A) remains the
same, but the subject uses two keyboard keys to adjust B until the
tones sound isochronous:
A-------B-------A-------B-------A-------B-------

I'm not new to E-Prime, but in the past I've always created standard
standard probe-response type tasks.  I have not tried to create a
program like this one before, where the participant has dynamic
control over the stimuli.

So my questions are the following:

1) Is it even possible to create this task in E-Prime?

2) Have you done something at all similar, and if so, how did you do
it?

3) If you haven't done anything like this, do you have any ideas about
how it could work?

My only thought is that perhaps I could set this up so that the two
tones are not actually 'continous' but presented in pairs over many
trials, and the temporal properties of trial n would be based on the
response to trial n-1.  However, I think this would create a delay
between the end of one 'loop' and the beginning of the next, which
would certainly affect the subject's perception of a continous
rhythm...

Any thoughts or suggestions would be greatly apprectiated.
Thanks!
Becky

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