EXPERIMENTAL TASKS AND PROCEDURE
An interventional study with dependent sample of MDD patients (n = 33) was carried out. The duration of the study was 4 weeks. MDD patients meeting exclusion/inclusion criteria were selected and medicated with an antidepressant. The patients were recruited from the psychiatry department of HUSM. Recruitment procedure was based on their willingness and was carried out by the researcher. Patients were given a demonstration about the experiment and research information (see Appendix 14) and an informed consent was given (see Appendix 2C). After signing the consent form, a data collection form was filled out based on their demographic information.
Fig. 3.3 explains the data collection scheme. Two types of data collection were involved: electrophysiological (EEG) data and clinical assessments using the HADS (Appendix 3A) and BDI-II (Appendix 3B) questionnaires. For EEG data, a wearable 24-channel cap and equipment were used. A total of five recording sessions of both types of recordings were performed. The first recording session, also known as the baseline, was carried out when the patients were unmedicated for at least the past two weeks. The second recording session was done one week after the start of medication. EEG recordings and clinical assessments were carried out after each week for the remaining sessions.
Figure 3.3 Data collection scheme.
EEG data collection consisted of the four steps seen in Fig. 3.4. A total of 40 minutes was required.
Step 1 was to set up the experiment using a 24-channel wearable cap. The suitable cap was selected by measuring patients’ head size using a head measuring tape. Proper setting up of the cap was important for data quality. This process took about 20 minutes.
Step 2 is eyes closed (EC) session: patients were required to sit on a chair with eyes closed and not fall asleep. This took about 5 minutes. Step 3 was the eyes-open (EO) session: patients were required to look at a fixation point (“+”) on a computer screen in front of them with minimal eye movements or blinking. This required nearly 5 minutes. Step 4 was a visual three-stimulus oddball task: patients were exposed to a random sequence of shapes on a computer screen. Only one shape was displayed at a time. There were a total of three shapes (Fig. 3.5): target
Figure 3.4 EEG data collection.
Figure 3.5 Visual three-stimulus oddball task.31
(a blue circle) with 5.0 cm size; standard (a blue circle) with 4.5 cm size; and distractor (a checker board) with 18.0 cm size.
Patients must respond to the target shape by pressing the SPACE key on the keyboard, but no action must be taken in response to other shapes. This process took about 10 minutes.