The Influence of Positive Emotion on the Degree Effect in Self-referential Processes: Evidence from ERPs

Self-reference effect refers to the accelerated process and better memorization by the individual when the information is involved with self-concept. However, previous studies have focused only on categorical differences, considering self-relevant effects as behavioral or neural activation differences between self-relevant and non-self-relevant stimuli. Thus, they failed to take into account the degree of self-relevance. In real-life situations, different correlations usually lead to various personal meanings, as the process of highly self-relevant stimulus has a more significant physical and social meaning than that of the minimally one. In addition, there are researches showing that self-relevant information is associated with positive emotional valence, that the individual inclines to attribute positive results and traits to personal characteristics and accounts the negative results or traits unrelated with their own personal characteristics. Therefore, investigating the influence of positive emotion on self-reference process is of great value. We adopted picture-priming paradigm, presented emotional pictures and self-reference stimulus with participants. To be specific, each trial was initiated by a cross appearing at the centre of the screen for 200ms followed by a blank screen whose duration varied randomly from 500 ms to 1000 ms. Then a picture from one of the two emotional pictures categories was presented for 500 ms along with black screen lasting randomly for 150~300 ms in sequence. Afterwards, 500 ms self-reference stimulus and 1000 ms black screen emerged. Subjects were instructed to identify the color of self-referential stimulus as fast and accurate as possible. If the color is blue, press the "1" key; if it is green, press the "2" key. Stimulus words would disappear after a keypress or automatically disappear after 1000ms. After the exercise experiment, the formal experiment concluded 360 trials divided into 3 blocks. Results of ERP showed that under positive emotional priming condition, the target stimulus elicited smaller P2 amplitudes than neutral condition, and highly self-relevant stimulus elicited a shorter P2 latency than any other stimulus. Furthermore, highly self-relevant names elicited larger N2 amplitude than moderately and non-self-relevant names, and under neutral priming condition, the target stimulus elicited longer N2 latency than positive emotional priming condition in frontal sites; highly self-relevant stimulus elicited longer N2 latency than any other stimulus conditions in the frontal and parietal sites. In the average amplitude of P3, highly self-relevant names elicited larger P3 amplitude than moderately and non-self-relevant names, and moderately self-relevant names elicited larger P3 amplitude than non-self-relevant names. Our results indicate human brain might not be sensitive on the processing of positive emotional stimulus. Self-referential processing demonstrates stability characteristics no matter whether in positive or neutral condition. Moreover, highly self-referential stimuli receive a more thorough and elaborate procession, with a representation of degree effect of self-referential processing.