**2.1. Emotional induction material and experimental instrument**

Materials include emotional induction materials, emotional intensity questionnaire, IA scale (Chen Internet Addiction Scale), and physiological signal acquisition equipment. Emotional pictures selected from International Affective Picture System (IAPS) [52], and emotional film clips selected from Taiwan corpora of Chinese emotions and relevant psychophysiological data [53] were utilized for emotional induction materials. Emotional pictures (anger, disgust, fear, sadness, happiness, and surprise pictures), and emotional film clips (anger, fear, sadness, happiness, and fear films) were adopted. Anger, sadness, and fear are negative emotions, while happiness and surprise are positive emotions. Participants rated their emotional intensity via questionnaire including happiness, sadness, disgust, surprise, fear, and anger, from 0 (lowest intensity) to 8 (highest intensity). DSM-5 IGD criteria and online game film clips as emotional induction materials were adopted for IGD experiment.

and recorded [54]. Third, in phase 2, emotional induction experiment was conducted, and participants were elicited by emotional induction materials [50, 51]. All physiological signals during the whole experimental period were acquired and recorded. These data acquired during the psychophysiological signal baseline was the stage of before emotional induction, and during the recording of the emotional induction was the stage of after emotional induction.

Investigation of Emotion Characters of Internet Abusers Using Psychophysiological Signals

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Data analysis method included statistics, such as correlation coefficient, T-test, and factorial ANOVA, and signal processing method for ECG and respiratory signals. ECG signals were processed and analyzed using an R-peak detection method. The RR intervals were transformed into an auto power spectrum, and the obtained HRV contained three frequency bands—high frequency (HF, 0.15–0.4 Hz), low frequency (LF, 0.04–0.15 Hz), and very low frequency (VLF, <0.04 Hz, excluding 0.00 HZ). Usually, HF indicates a parasympathetic nervous response and LF indicates a sympathetic nervous response. The RSA value was calculated as HF/((HF + LF)). Complementary Ensemble Empirical Mode Decomposition (CEEMD) which has been validated to be suitable for respiratory signals was applied to decompose respiratory signals [55]. CEEMD can acquire high frequency (HF, muscle contraction frequency), dominant frequency (DF, main respiratory frequency), and power of each respiratory signal. We are curious about the responses or reaction intensity (normalized power difference value) to several emotional stimuli from different time scale materials of IA abusers. The value of normalized power difference upon before and after the emotional inductions indicated the respiratory amplitude (emotional intensity), and the trend of difference implied the positive and negative respiratory

responses. The differences in TAM, ECG (RSA) between HIA and LIA were examined.

No statistical difference in age and gender existed whether in IA experiment or in IGD experiment. The consistency of CIAS scoring, IGD scoring, and emotional intensity among participants was tested, and results (Cronbach's alpha values) were acceptable [56]. Regarding the results of respiratory signals, the normalized power differences of high frequency (HF) and dominant frequency (DF) varied along different emotions. The HIA and the LIA groups also exhibited different normalized power differences among some emotions. Respiratory amplitude and frequency implied the emotional intensity of physiological reaction. In the HIA group, the power differences of DF in positive and negative emotional states were less consistent than those in the LIA group, and the trends of difference were almost opposite. The emotional effects on respiratory amplitude almost positively affected the HIA group but negatively affected the LIA group. The results of trends of respiratory power difference suggested that when HIA group in whether negative or positive emotional states, their thoracic movement was mainly responsible for respiratory regulation, whereas LIA group mainly used abdominal movement to regulate respiration [30]. Concerning the autonomic nervous response, the results of RSA and HRV indicated that the RSA base of the HIA group was lower than that of the LIA group. Hence, the HIA group did not tend to express positive emotions. They may express negative emotions rather than positive emotions, and did not suppress negative

**2.3. Data analysis and result**

**2.4. Result**

Internet addiction (IA) is usually evaluated using self-reported questionnaires, scales, or interviews. Chen Internet Addiction Scale (CIAS) [4], a well-developed and widely applied scale, was adopted. CIAS consists of 26 items and is a self-assessment scale including five dimensions of Internet-related symptoms and problems, namely symptoms of compulsive use, of withdrawal, and of tolerance, and problems in interpersonal relationship, and in health/time management. People can be classified into high-risk IA (HIA) or low-risk IA (LIA). The nine IGD criteria were used in IGD experiment. The cut-point was five, and people with the score over five were IGD.

Physiological signals including respiratory signals, ECG signals, and facial images were collected. Respiratory signals of thoracic movement (TM), abdominal movement (AM), and thoracoabdominal movement (TAM) were acquired using two respiratory belts with sampling rate at 1000 Hz (SS5LB, BIOPAC Systems, Inc., Goleta, USA). The belts were encircled at the level of armpit (TM, channel 1, C1) and navel (AM, channel 3, C3). Electrocardiography (ECG, with three disposable pregelled Ag/AgCl spot electrodes) was used with electrodes applied to the surface of a participant's skin. ECG signals were sampled at 1000 Hz and acquired using the DAQcard (USB 6218, National Instruments Corp., Austin, USA). Facial images were captured using a webcam (Logitech V-UBK45, USB 2.0, 10 fps, 640 × 480 resolution, Switzerland).
