Overview

While the onset of an auditory stimulus can be marked by having the stimulus presentation computer send event markers via USB, timing will be more accurate and setup would be simpler if one took advantage of StimTracker’s built-in audio marking capability. Instead of connecting the computer to external speakers like this:

You can route the signal via StimTracker:

Connection

You will need the (included) “Audio Pass-Through Cable” to connect StimTracker to the speakers. Connect this cable between the audio output on your computer and the “Audio In” on StimTracker. Then plug the speakers into the “Audio Out” connector.

When wired this way, StimTracker monitors the auditory level and sends an event marker to the EEG recorder when the volume rises above a preset threshold. The auditory signal is not altered – only monitored. 

Adjusting Thresholds

See Using the Front Panel for information on setting the threshold. You can set the thresholds independently for each of the right channel and left channel.

Researchers use all sorts of auditory stimuli in their experiments. They can be largely separated into two groups: human speech and computer generated tones. Both can have their own peculiarities. Computer generated stimuli may consist of a single tone or a series of tones. In the latter case, StimTracker will generate an event marker for each tone, which may not be what you want. For human speech, the stimulus may be a single word. But it can also be a sentence that contains pauses, and StimTracker may end generating an event marker for each pause. You can tailor the generation of event markers to your liking by using filters.

How Event Markers Are Delivered

The most common application is to use m-pod. m-pod takes the multiplexed signals that StimTracker delivers and converts it into TTL output. By default, the output is “reflective”. This means that if the length of the auditory stimulus is, say, 100ms, the width of the TTL output pulse will also be 100ms. It is possible to change this behavior so that a shorter pulse is delivered on onset and another one is delivered on offset.

StimTracker can also deliver time-stamped event marker information via USB; this is turned off by default but you can easily enable it.

On StimTracker Quad model only, event markers are also delivered via the “TTL Output” connector. Unlike with m-pod, output on this connector is always in “reflective” mode and cannot be changed.

Back to StimTracker Support main page
Last Revision: Apr 24, 2020