The time of 5 minutes. At this phase, the

The task performed in this study was based on arithmetic task described in detail in 52. The task designed and presented in MATLAB with Graphical User Interface (GUI). It involved 3-single digit integer (from 0 to 9) and used the addition (+) or subtraction (–) operands (for example 2-3+9).  The answers were presented in the sequence of 0 to 9 and participant has select the right answer by doing single-click using the mouse. The task was performed at three phases; training, control and stress phase, each of the phase has its own conditions.  During training phase, participants practiced the arithmetic task for a total duration time of 5 minutes. At this phase, the percentage of answering the task correctly and the time taken by each individual to answer each question was recorded. Subjects with poor performance were not counted for this study. Then, the average recorded time was reduced by 10% and used as time pressure to stress the participants.  During the control phase, EEG+fNIRS probe holder was attached to the participant’s head and signals were simultaneously recorded for a total duration of 5 minutes. At this phase, each of the participant was instructed to solve the arithmetic problems as fast as he can but without any time limit per question. At the end of the control phase, participants filled up self-report questionnaire about workload using NASA-TLX 53 described in the next sub-section. During the stress phase, simultaneous measurement of EEG+fNIRS were recorded for a total duration of 5 minutes. At this phase, each of the participant solves the arithmetic problems under time pressure (the average time taken in the training phase which reduced by 10%). Beside the time pressure, feedback of answering the questions (“correct”, “incorrect” or “timeout”) were displayed on the computer monitor to further induce stress in the participants. Additionally, performance indicators (one for the participant’s performance and one for the averaged peer performance fixed at 90% accuracy) were shown on the monitor to induce more negative emotional stress. At the end of the stress phase, participants filled up another NASA-TLX self-report questionnaire about the task loading. Figure 1 summarizes the overall experimental procedures. A block design that incorporated both; the control and the stress tasks was used in the presented study. A total of 10 blocks were used (5 blocks in the control phase and 5 blocks in the stress phase). In both phases; control and stress, the arithmetic tasks in each block was display for 30 seconds followed by 20 seconds rest. During the 20 s rest, participants instructed to focus on a fixation cross with black background to sustain their attention to the monitor display. The order of the task conditions was presented randomly. The reaction time and the accuracies of answering the task under the control and the stress phases were recorded and used for analysis of behavioural data. All participants report they were relax and peaceful during the control-workload and were stressed while performing the task under stress condition.

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