Startle modification is a robust phenomenon that has been used as a tool in the research of emotion and motivation. In a picture viewing paradigm, valence of affective pictures modulates startle magnitude. There is a debate on whether emotional or attentional processes are the mechanism of startle modification. The present study sought to address this question by investigating the individual differences related to startle modification and explore the relationship of the trait-like physiological variables and startle modification. The study creatively calculated standardized startle scores and treated personality variables as continuous variable. The results showed that specific contents of the affective pictures had different effects of startle modification. Personality variables influence the startle modification in emotion conditions differently. Cardiac activities were related to raw startle magnitude but not to startle modification. The results have suggested that there are the influences of individual differences in attention and effortful control on startle modification and attention and that emotion and attention interact with each other in startle modification. The study filled gaps in the research on startle modification and personality and guided future studies of this topic. / Master of Science