Emotional Valence Intensity Effect And Its Neural Correlates

In addition to differences in category and valence polarity, the emotion people experience in life settings are also diverse in valence intensity. Anecdotal evidence suggests that negative emotions of diverse strength have different impact on human life and cognitive processes. This dissertation investigated the human sensitivity to valence intensity differences in emotional stimuli, and individual differences in brain susceptibility to emotional stimuli of diverse strength by manipulating the valence strength of emotional stimuli. Using the two-choice oddball task that is famous for ecological validity of emotional susceptibility studies, this dissertation was composed of 4 ERP studies. Study 1 investigated the human sensitivity to valence differences in emotional stimuli and the neural substrates underlying the emotional valence intensity effect. Study 2 investigated the influence of negative emotion of diverse valences on visual processing of rare novel events and its related temporal features. Using two ERP experiments, Study 3 investigated the neural mechanisms underlying the female advantage in identifying negative emotions, and neurophysiological correlates of the females'higher prevalence of affective disturbances by focusing on gender differences in emotional susceptibility to emotional stimuli of varying valences. Study 4 investigated how extraversion, a personality trait that describes the degree to which a person is outgoing, sociable, and interactive with other people, influences the human brain sensitivity to emotionally positive and negative stimuli, and the neural mechanism underlying extraverted people's higher degree of personal happiness. All subjects recruited for these studies were healthy college students, and stimulus materials were emotional images selected from International Affective Picture System (IAPS) and Chinese Affective Picture System (CAPS). The results were as follows.1.The human brain is in particular sensitive to valence intensity changes in emotionally negative stimuli, while is relatively insensitive to valence intensity changes in positive stimuli. This effect is termed by the dissertation as emotional valence intensity effect, whose generation is likely to be mediated by the right hippocampus and amygdala complex.2.Consistent with description of emotional valence intensity effect, negative emotional contents of diverse strength have distinct impact on visual processing of rare novel events. This influence is observable not only at early attentional orienting but also at later context updating and response decisional stages. This suggests that the emotional valence intensity effect, to some extent, is stably existent and may be an inherent characteristic of the human emotional activity.3.While the existence of the emotional valence intensity effect is relatively stable, its manifestation is obviously influenced by individual difference factors such as gender, and emotion-related personality trait like extraversion. While males and females, generally speaking, are similar in emotional susceptibility to highly negative stimuli and to positive stimuli of diverse valences, females are more susceptible to negative stimuli of lesser saliency compared to males. This may be associated with the female advantage in identifying negative emotions and with the females'higher prevalence of affective disturbances. The increased brain susceptibility of females to mild negative stimuli is likely to be mediated by the right orbitofrontal cortex.4.Extraverted people are more emotionally reactive to positive stimuli compared to non-extraverted individuals, irrespective of the valence intensities of positive stimuli. On the other hand, extraverts are less susceptible to negative emotional stimuli of lesser saliency compared to control subjects. Therefore, the increased brain bias for positive emotional events and decreased susceptibility to moderately negative stimuli may account for the higher levels of subjective wellbeing in extraverts.In summary, there is an emotional valence intensity effect in the human emotional activity that the human brain is in particular sensitive to valence differences in negative stimuli while the brain is relatively insensitive to those in positive stimuli. This effect, possibly as an inherent characteristic of the human emotional activity, is stably existent, and the negative emotion of different strength has distinct impact on visual novelty processing. Despite its stability, biological sex, as well as the trait of extraversion, influences the manifestation of the emotional valence intensity effect, in particular, through modifying the human sensitivity to mild negative stimuli or to positive stimuli of diverse valences.