Knowledge Base

Add a Custom External Device

Aim

To control a device that cannot communicate with The Observer XT using the Noldus communication protocol N-Linx. Examples of such devices are older versions of MediaRecorder and FaceReader, some physiological data acquisition systems, and some eye trackers.

Note: BIOPAC AcqKnowledge 5, Tobii Pro Studio, Tobii Pro Lab, Tobii Glasses software, and the Bitbrain EEG acquisition software can be controlled using N-Linx, which simplifies data acquisition and ensures synchronization with events with the acquired data. See the following technical notes available for download from the MyNoldus section of the Noldus website:

• Technical Note - BIOPAC MP System - The Observer XT
• Technical Note - Tobii Pro Eye Trackers - The Observer XT
• Technical Note - Tobii Glasses - The Observer XT
• Technical Note - Bitbrain EEG - The Observer XT

Prerequisite

The external device can be controlled with a command line.

General Procedure

1. Choose Setup > Project Setup. Under Observation Source, select Live Observation.
2. The Devices window opens. If not, click the Devices button. Click the Add External Program button at the bottom of the table.
3. Enter a name for the action, for example, Control MediaRecorder 3.
4. Under At:, select when you want the program to run. The action will be defined in step 5.
5. In each of the three rows, click the button next to the Program field and browse to the program to control.
6. In the Command Line Options field, enter the command to be carried out, for example /R in the Start Observation row for MediaRecorder 3. You can also enter the following commands in the Command Line Options field:
   • %ON% – Enters the current observation name in the command line.
   • %SN% – Enters all available subject names in the command line, separated by spaces.
   Use these options to, for example, run a batch file and enter the current observation name or the subject names in the file name it produces. It is not possible to combine these options with other commands in the command line.
7. There may be a delay between the observations and the commands being carried out in the external program. Enter this delay in the ms. before fields. The Observer XT will then send the commands the specified time before the observation starts or ends. See also: How Do I Determine the Delay?
8. Click OK. The Devices window shows the newly added action of the external program. Select the checkbox in front of it. Click Edit Settings to change this action. To rename or delete an action, right-click the corresponding row and select the option.
9. To add more actions, repeat steps 2 through 9 for each external program.
10. Optionally, set up Automatic Linking of Digital Media Files to automatically import videos created by the external program into the observation.

• For detailed procedures for older versions of MediaRecorder or FaceReader, consult the Reference Manual of that version.
• Videos created by MediaRecorder 2.5 or higher are automatically synchronized with the Event Log when you import them in The Observer XT.

How Do I Determine the Delay?

1. Carry out a test observation and make sure that with The Observer XT you score some conspicuous event that is also visible in the imported video or data file. For example, you record pressing a key on video.
2. Manually synchronize the event log and the imported file using the logged event. See Manual Offset.
3. Open the File Synchronization window (see Numerical Offset); the offset of the data file relative to the event log is displayed here.
4. Enter this value in the ms. before fields in step 7 of Add a Custom External Device.

Note: For complex lab setups with various external applications, you can use the Noldus SyncBox to facilitate determining this delay. See the SyncBox - The Observer XT Technical Note, available for download from the Noldus website.