Auditory Brainstem Response (ABR) with Stimtracker and STIM2

Hardware General
1

Hello,

I’m currently trying to create a protocol for ABR testing with the Compumedics software (STIM2) and the StimTracker. I’m using the STIM2 software to generate both the audio stimuli and the triggers pulses which are being sent to the Neuroscan Synamps RT EEG unit. According to the user manual the STIM2 software sends 2 triggers - one directly to the acquisition software (via USB port) and another (more accurate one) via the StimTracker through the auditory signal using a threshold detection method. Does anyone know any more about this detection threshold method? I am only getting an lit LED on the front of the StimTracker if the threshold is set to 1…

Furthermore, I’m having some trouble with the alignment of the trigger pulses, when I view these on an oscilloscope neither of them are aligning with the click stimulus at all (which is not consistent with what is going on in the STIM2 software).

If anyone could provide any help, it would be much appreciated!

Regards,
Julien

2

Regarding setting the threshold to 1, this is common with StimTracker when it comes to computer generated tones. The reason is because the audio circuitry in StimTracker was designed and optimized to handle human voice and recordings. It’s a tradeoff: if we had made the audio circuit more sensitive so that it can pick up ABR tones, then this would have resulted in false markers being generated when playing human voice.

I am surprised by your findings regarding the oscilloscope. For maximum speed and no jitter, we designed the analog inputs in StimTracker to be pure electronics, i.e. no interference from the microprocessor except to set the threshold. I would appreciate it if you can post additional information about your oscilloscope findings.