Using Cedrus StimTracker with Inquisit

Inquisit has built in support for interoperating with Cedrus StimTracker devices. The StimTracker provides an alternative to the parallel or serial port for Inquisit to communicate with external neurophysiological measurement systems and send markers of significant events during stimulus presentation. Inquisit can interoperate with a StimTracker on both Windows and Mac platforms.

The first step in using the StimTracker is to plug it into a USB port on your computer and install the device driver (which you can download from Cedrus' web site).

Once the device is plugged in, you can interface with it in Inquisit as if it were a type of stimulus. In other words, you can send signals to the device using syntax similar to that which displays pictures or text or plays a sound. By presenting the StimTracker signals at the same time as other stimuli, the StimTracker can relay the signals to an ERP of fMRI system in order to mark stimulus onsets.

To signal a StimTracker, you will need to define xid elements. The following xid element has a single item with a value of 0 (all TTL channels set to low):

<xid stblank>
/ product = stimtracker
/ items = (0)

The following two xid elements are functionally identical, each containing 3 signals with values 1, 2, and 4. The two elements illustrate the two different ways in which signal values can be defined - as integers or as binary strings.

On each trial, the select attribute for the xid elements determines which signal is sent on a given trial. In both cases, selection is linked to the selected item in the text element named "letters". The letters text element selects randomly without replacement from items "A", "B", and "C". The xid elements select the corresponding values. Thus, when "A" is selected, xid value 1 is selected. When "B" is selected, xid value 2 is selected. When "C" is selected, xid value 4 is selected.

<xid stsignalint>
/ product = stimtracker
/ items = (1, 2, 4)
/ select = current(letters)

<xid stsignalbin>
/ product = stimtracker
/ items = ("00000001", "00000010", "00000100")
/ select = current(letters)

<text letters>
/ items = ("A", "B", "C")
/ select = noreplace

The following xid element defines a Lumina fMRI response pad that is also plugged into the presentation computer.

<xid rb>
/ product = lumina

The following trial demonstrates how to present the signals and text as well as record the response from the Lumina reponse pad. The trial presents a signal that is synchronized to the onset of the text stimulus. The signal is reset to 0 after 3 vertical retrace intervals (50 milliseconds on a 60hz monitor). Note that pretrialsignal is defined so that the trial waits for a signal value of 1 from the parallel port before running. This is handy for synchronizing trials on the presentation machine with fMRI recording blocks.

<trial target>
/ pretrialsignal = (LPT1, 1)
/ stimulusframes = [1 = letters,stsignalint; 4=stblank]
/ inputdevice = xid(rb)
/ validresponse = (4)