Synchronizing auditory and visual stimulus using PC sound card

[Roland Loeffen]

Hi all,

For an experiment with an acoustic startle, we need to sync a visual stimulus with an auditory startle stimulus. I have been looking at the MATLAB Psych toolbox which is especially designed for these kind of experiments.
When testing, i found large delays between visual and auditory stimulus. Looking at the manual and the browsing the internet for more information I found that the hardware can have a large delay which can be minimized by using soundcards with native ASIO on board an the appropriate drivers. When using ASIO drivers with a standard PC with on board sound card i still find a delay of 50+ ms.

I am now thinking of buying an professional external sound card used mainly for recording sound with minimal delay and special ASIO drivers.

My question if anyone has experience with this kind of experiments and knows if this will minimize the delay below a couple of ms. And does anyone have other suggestions to set up this experiment?

Thanks in advance,

Roland

Roland Loeffen, Msc
Technical Manager Motion Laboratories
Department of Rehabilitation Medicine,
Radboud University of Nijmegen Medical Center,
P.O. Box 9101, 6500 HB Nijmegen
The Netherlands
E-mail: R.Loeffen@reval.umcn.nl
Tel: +31-24-3668427
Secr: +31-24-3614804
Fax: +31-24-3619839

[Gaspar Morey Klapsing]

Re: Synchronizing auditory and visual stimulus using PC sound card

Dear Roland,

You could try to place the audio signal (generated externally) on a free channel of your Data Acquisition Board and use this as a trigger.
We once did something similar, allthough we did not care that much on ms delay. However it may work easily if you can generate the sound from outside the PC (another PC, a video stream, a manual trigger, etc).
In our case we placed an audio signal (buzz) on a video and used it to synchronise our motion analysis system with the the videos sequences seen by the subjects. The video display was independent of the motion analysis system, but the sound channel of the video went directly to the AD board of the motion analysis system. At least until there no delay is to be expected and no special Soundcard would be needed.

Hope this helps.

Good luck,

Gaspar

Gaspar Morey Klapsing (PhD)
Head of the lab for functional footwear analysis at INESCOP
07300 Inca, Balearic Islands, SPAIN

Email: gmorey@inescop.es
Tel: +34 971 507 098

[Alan Armstrong]

Re: Synchronizing auditory and visual stimulus using PC sound card

Hi,

I recently did an experiment using a Visual stimulus assessing coordination. I plan on building on this experiment and assessing multisensory interaction with Visual and Audio stimuli, similar to your research. Currently I am using a program that was created from scratch by a programmer using C++, it creates audio and visual stimuli that are synched.

May I ask what software you are using for the visuals? Is it matlab as well? I have used labview before and to be honest it was a bit tricky to create clean graphics but you could set everything up to minimise the delays using specified loops etc.

Have you tried using processing before? I have worked with it and generally if you are any good with the code it can be effective?

regards,

Alan

[Richard Ellis]

Re: Synchronizing auditory and visual stimulus using PC sound card

Hey,

You could also consider doing it on the hardware end. The audio out jack for standard computer speakers generates an analog voltage signal. You could use an amplifer and use that standard voltage to power a simple visual stimuli (a few bright LED's for example). Just an idea.

-Rich

[Venn Ravichandran]

Re: Synchronizing auditory and visual stimulus using PC sound card

Roland,

As someone who ran acoustic startle experiments previously, I would strongly recommend using external hardware. You can still use your computer's sound card to trigger a digital pulse that would then trigger a digital relay, that turns on speakers and your visual stimulus (both driven by external sources). The right speakers will get you a rise time of < 1ms; also, I would think that to get startling acoustic stimulus, you will need a power supply of >5V available from your computer.

Cheers,
-Venn