Stimuli

In the current study, to induce happy and sad moods, we selected 20 pieces of music from the Chinese Affective Music System (CAMS), which was a standard set of music stimuli for emotional research with Chinese participants³⁸. In the 20 pieces of music used in the current study, half of them were supposed to induce a sad mood while the other half were supposed to induce happy mood. The 10 happy music excerpts were significantly higher than the sad excerpts in the rating of happiness and arousal (Happiness: 6.93 ± 0.30 and 3.55 ± 0.73, p < 0.001; Arousal: 6.89 ± 0.40 and 4.05 ± 0.66, p < 0.001). No significant difference was found in the rating of expression and length (Expression: 5.35 ± 0.54 and 5.02 ± 0.64, p = 0.652; Length: 62.50 ± 4.43 s and 61.9 ± 4.79 s, p = 0.103).

The visual stimuli used in the experiment were pictures showing a person’s hands/forearms/feet in painful or non-painful situations, which have been used in previous ERP studies³⁹. All the situations depicted in these pictures were ordinary events in daily life. All the events showing in the non-painful pictures were corresponding to those in the painful pictures, but without the nociceptive component (Fig. 1A). There were 60 painful pictures and 60 non-painful pictures in total. All of them had the same size of 9 × 6.76 cm (width × height) and 100 pixels per inch. Luminance, contrast, and color were matched between painful and non-painful pictures. Previous studies have confirmed that the painful and non-painful pictures were significantly different on the dimensions of pain intensity and emotional valence, according to the self-reported rating.

Examples of picture stimuli (A) and Procedures of the experiment (B).