ECG & EEG features for mental workload and multilevel stress classification in different sexes

Description

The data were collected from 66 healthy university students (21 males, 24 females in the follicular phase of the menstrual cycle, and 21 females in the luteal phase of the menstrual cycle) . The Montreal Imaging Stress Task (MIST) was modified and used in this study. A series of computer-based mental arithmetic tasks is designed to evaluate responses in control and stressful conditions. The experiments thus conducted in two separate sessions for the two conditions, which were two weeks apart. Each of the 2 sessions consisted of 7 periods: training, eyes open (EO), mental arithmetic task (MAT) on 4 consecutive levels of difficulty (arithmetic calculation level 1, AC1–arithmetic calculation level 4, AC4), and recovery. The control condition started with a training period to familiarize the subject with the experimental procedure, during which ECG and EEG signals were not recorded. During this period, the subject was presented with a series of computerized sampled questions at 4 difficulty levels of mental arithmetic tasks. Answer choices for every question were displayed on a computer screen in a sequence of integers between 0 and 9. The subject was requested to use a wireless computer mouse to click on the correct answer. Following the training period, the recordings started, and the subjects were asked to sit in a relaxed position with no movement and to focus on a black dot displayed on a computer screen for 5 minutes (the eye-open, EO, period). These requirements were critical to constructing a reliable EEG baseline with the minimum amount of artifacts caused by eye and body movements. After that, an instruction to perform mental arithmetic calculations was shown on the computer screen. The mental arithmetic task is composed of 4 levels of difficulty. Each level lasted 5 minutes. Level 1 (Arithmetic Calculation Level 1 – AC1): addition (+) and subtraction (-) of 3 single-digit numbers, e.g., 7-4+1. Level 2 (Arithmetic Calculation Level 2 – AC2): addition (+), subtraction (-), and multiplication (x) of 3 single- and double-digit numbers, e.g., 6x8-30. Level 3 (Arithmetic Calculation Level 3 – AC3): addition (+), subtraction (-), and multiplication (x) of 4 single- and double-digit numbers, e.g., 35+10-4*8. Level 4 (Arithmetic Calculation Level 4 – AC): addition (+), subtraction (-), multiplication (x), and division (/) of 4 single- and double-digit numbers, e.g., 96/4x2-11. No time limit or negative feedback messages were given to the subjects. After each question, the correct/incorrect message was displayed. After the AC4 period, the subjects relaxed and sat still for 5 minutes (the recovery period). ECG and EEG signals were recorded from the beginning of the EO period until the end of the recovery period. The protocol for the mental-stress condition was the same as it was for the control condition, but with a time limit and social evaluative threat components introduced. Several negative feedbacks were introduced to actively induce stress.

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