The current thesis aims to advance the theoretical and empirical understanding of the temperament trait Sensory Processing Sensitivity (SPS). Since its discovery and development in 1997, much research has investigated the sensory, perceptual, and emotional behaviours and experiences associated with SPS, as well as its negative and positive outcomes. This research focuses specifically on three behaviours/experiences that, to the author’s knowledge, have been under-researched. Study One explores the perceptual ability of Highly Sensitive Persons. This investigation tested the associations of SPS with the perception of visually degraded words. The study found that the positive facet of SPS positively correlated and predicted the detection and identification of degraded words, tested at three levels of difficulty. In Studies Two and Three, the dreaming experiences of Highly Sensitive Persons are investigated. In particular, a cross-sectional study of SPS, dreams, and nightmare experience was conducted, as well as a longitudinal study of how daily life emotions can impact on the emotions experienced in dreams. Finally, Study Four considers the avoidance of violence. Item 18 of the Highly Sensitive Person Scale states that high SPS is associated with the avoidance of violence in television shows and movies, although this item has received no empirical validation since the development of the questionnaire. Due to the potential impact of witnessing violence on the emotional experiences of Highly Sensitives, a behavioural investigation was conducted to explore responses to viewing violence in fictional movies and real-life videos. This study confirmed the validity of Item 18. Importantly, most studies in the thesis controlled for the Big Five traits, as SPS has been recently claimed to be solely a combination of openness to experience, neuroticism, and introversion. The thesis provides evidence of the separability of SPS from these traits.