Thesis - Instituto de Telecomunicações

3.4. MATERIALS AND METHODS 57Figure 3.14: EEG positioning places based on the 10-20 system.CameraThe acquisition setup was also composed of a web cam directed to the subjects face. Thepurpose of acquiring video information was to be able to verify potential events of the testrealization and to confirm eventual occurrences in the signals. The webcam was modifiedin order to have a LED attached and visible in the view field. The LED was connectedto the mouse button and it turned off when the subject pressed the mouse button. Thiswas created for synchronization purposes, ensuring that all the signals had a common timereference.3.4.5 Experts and Data AnnotationEach subject performing the tests, was prepared and instructed by two experts on electrophysiologicalsignals acquisition, that supervised the realization of the complete set of tests.There were two computers connected to the subject’s computer via Ethernet. The expertsused a special web page (depicted in figure B.12 in annex B) that permitted occurrenceannotation for posterior tests interpretation. The interaction with this page was also monitoredusing the WIDAM system and when the expert clicked in a button at the page, acomment was added to the interaction file. The annotations could be related to the usercognitive strategy or to the emotional state. The expert could also produce written annotationfor some other events that occurred (such as external noise or any kind of interruption).