Indeed, it was found that American preschoolers preferred excited smiles and perceived them as happier than Taiwanese children did, and these values were seen to be mirrored in storybook pictures. Importantly, it was shown that across cultures, exposure to story books altered children's preferences. Thus, a child exposed to an exciting (versus calm) book, would alter their preference for excited (versus calm) activity. This shows that children are largely malleable in their emotions, and suggests that it takes a period of time for cultural values to become ingrained. Another study has shown that American culture values "high arousal positive states" such as excitement, over "low arousal positive states" such as calmness. However, in Chinese culture "low arousal positive states" are preferable to "high arousal positive states". The researchers provide a framework to explain this, suggesting that "high arousal positive states" are needed in order to influence someone else, where "low arousal positive states" are useful for adjusting to someone else. This explanation is in line with the collectivism-individualism dichotomy: American values promote individual autonomy and personal achievement, where Asian values promote relational harmony. Emotion expression is consequently seen to be influenced largely by the culture in which a person has been socialized. Nisbett & Cohen's 1996 study "Culture of Honor" examines the violent honor culture in the Southern states of the USA. The study attempts to address why the southern USA is more violent, with a higher homicide rate, than its northern counterpart. It is suggested that the higher rate of violence is due to the presence of a 'culture of honor' in the southern USA. A series of experiments were designed to determine whether southerners got angrier than northerners when they were insulted. In one example, a participant was bumped into and insulted, and their subsequent facial expressions were coded. Southerners showed significantly more anger expressions. Furthermore, researchers measured cortisol levels, which increase with stress and arousal, and testosterone levels, which increase when primed for aggression. In insulted southerners, cortisol and testosterone levels rose by 79% and 12% respectively, which was far more than in insulted northerners. With their research, Nisbett & Cohen show that southern anger is expressed in a culturally specific manner. One of the biggest challenges in cultural research and human emotions is the lack of diversity in samples. Currently, the research literature is dominated by comparisons between Western (usually American) and Eastern Asian (usually Japanese or Chinese) sample groups. This limits our understanding of how emotions vary and future studies should include more countries in their analyses.