insanity in court. It is unclear whether increased rates of the disorder are due to better recognition or sociocultural factors such as mass media portrayals. The typical presenting symptoms in different regions of the world may also vary depending on culture, such as alter identities taking the form of possessing spirits, deities, ghosts, or mythical figures in cultures where normative possession states are common. The possession form of dissociative identity disorder is involuntary and distressing, and occurs in a way that violates cultural or religious norms. Definitions Dissociation, the term that underlies dissociative disorders including DID, lacks a precise, empirical, and generally agreed upon definition. A large number of diverse experiences have been termed dissociative, ranging from normal failures in attention to the breakdowns in memory processes characterized by the dissociative disorders. It is therefore unknown if there is a commonality between all dissociative experiences, or if the range of mild to severe symptoms is a result of different etiologies and biological structures. Other terms used in the literature, including personality, personality state, identity, ego state, and amnesia, also have no agreed upon definitions. Multiple competing models exist that incorporate some non-dissociative symptoms while excluding dissociative ones. Due to the lack of consensus regarding terminology in the study of DID, several terms have been proposed. One is ego state (behaviors and experiences possessing permeable boundaries with other such states but united by a common sense of self), while the other term is alters (each of which may have a separate autobiographical memory, independent initiative and a sense of ownership over individual behavior). Ellert Nijenhuis and colleagues suggest a distinction between personalities responsible for day-to-day functioning (associated with blunted physiological responses and reduced emotional reactivity, referred to as the "apparently normal part of the personality" or ANP) and those emerging in survival situations (involving fight-or-flight responses, vivid traumatic memories and strong, painful emotions – the "emotional part of the personality" or EP). "Structural dissociation of the personality" is used by Otto van der Hart and colleagues to distinguish dissociation they attribute to traumatic or pathological causes, which in turn is divided into primary, secondary and tertiary dissociation. According to this hypothesis, primary dissociation involves one ANP and one EP, while secondary dissociation involves one ANP and at least two EPs and tertiary dissociation, which is unique to DID, is described as having at least two ANPs and at least two EPs.