Evidence Against Inter-Identity Amnesia

1. Serial reaction time task M Z X N Introduction Evidence Against Inter-Identity Amnesia Limitations of These Studies • Dissociative Identity Disorder (DID) is defined as “a failure to integrate various aspects of identity, memory, and consciousness.” • It affects 1% of the population, making it as prevalent as other debilitating mental health disorders such as schizophrenia • DID patients lose their lives to suicide at a higher rate than patients suffering from any other psychiatric disorder. • Two conflicting theories • Posttraumatic model – personality is divided as a protective reaction to trauma. Memories of traumatic events are stored in dissociated states. • Sociocognitive model – multiple identities are created and maintained in response to therapist influences, media portrayals and cultural expectations. • DID often involves various types of amnesia • Loss of memory for current episodes • Loss of autobiographical memory (usually from childhood) • Appearance of pseudo-memories • Symmetric amnesia • Asymmetric amnesia • Only people who could fully control and maintain identity switch were chosen. • Not all identities for each patient were tested. • Patients were chosen so that one of the identities did not know of the others. • Small sample sizes, typically less than 30 cases at once, were tested. • It is often difficult to tell if the memory tests were measuring the proper form of memory and nothing else because simulation is possible. • Patients did not come from a very diverse background. • Details about subjects were largely based on self-report. Interidentity amnesia for neutral, episodic information in dissociative identity disorder Huntjens et al, 2003 Procedure Subjects (31 DID patients, 25 controls, and 25 simulators) were taught two word lists as shown below. Can Inter-Identity Amnesia in Dissociative Identity Disorder be Accurately Described by Current Studies?Ioanna Georgopoulos (Writing and Speaking Science, Eng 391, 2009) • Sample word lists are shown at right • The researchers used two unshared categories, vegetables and animals. • An unshared category was used as a control. List A contained names of flowers and list B of furniture. • Patients showed interference between words learned in list A and list B. • Interference indicates that words from list A taught in personality one were recalled by personality two. • Patients showed a reduced capacity to recognize and recall words in general. Conclusions • Results show that inter-identity amnesia does not occur. • However, patients do report having no knowledge of events taking place in other personalities. • It is possible that patients have an incorrect belief about their memory function, not a problem with the memory function itself. Inconclusive Evidence Regarding Inter-Identity Amnesia Directed forgetting between, but not within, dissociative personality states Elzinga et al, 2003 Procedural memory in dissociative identity disorder: When can inter-identity amnesia be truly established? Huntjens et al, 2005b Future Experiments • Procedure • Subjects (31 patients, 25 simulators, and 25 controls) were given a serial reaction time task (shown below). • The task involves pressing the letter on the keyboard that corresponds to the position on the screen (Z,X,N,M). • Response time was measured and analyzed across trials. • Procedure • 12 DID patients were tested on a directed-forgetting task. • They were taught nonsense word pairs and told to specifically remember or forget them when switching states. • Experiments should be simulation-resistant to focus on actual memory processes. • Limitations on subjects should be relieved to increase the sample size. • More objective memory tests need to be devised to avoid patient bias. • fMRI studies should focus on changes between personality states. Problem Does inter-identity amnesia occur in dissociative identity disorder patients? Results Method • Pubmed was used with search terms “dissociative identity disorder” and amnesia • The resulting articles were then limited to those produced in the last ten years. References Results Bear MF, Connors BW, Paradiso MA (2001) Neuroscience: Exploring the Brain. Lippincott Williams & Wilkins. 2nd Edition. Dorahy MJ (2001) Dissociative identity disorder and memory dysfunction: the current state of experimental research and its future directions. Clinical Psychology Review 21(5): 771-795. Elzinga BM, Phaf RH, Ardon AM, van Dyck R (2003) Directed forgetting between, but not within, dissociative personality states. Journal of Abnormal Psychology 112(2): 237-243. Forrest KA (2001) Toward an etiology of dissociative identity disorder: A neurodevelopmental approach. Consciousness and Cognition 10: 259-293. Huntjens RJC, Peters ML, Postma A, Woertman L, Effting M, van der Hart O (2005a) Transfer of newly acquired stimulus valence between identities in dissociative identity disorder (DID). Behaviour Research and Therapy 43: 243-255. Huntjens RJC, Peters ML, Woertman L, Bovenschen LM, Martin RC, Postma A (2006). Inter-identity amnesia in dissociative identity disorder: a simulated memory impairment? Psychological Medicine 1-7. Huntjens RJC, Postma A (2003) Interidentity amnesia for neutral, episodic information in dissociative identity disorder. Journal of Abnormal Psychology 112(2): 290-297. Huntjens RJC, Postma A, Woertman L, van der Hart O, Peters ML (2005b) Procedural memory in dissociative identity disorder: When can inter-identity amnesia be truly established? Consciousness and Cognition 14: 377-389. Merck Manual (1995-2006). Merck & Co., Inc., Whitehouse Station, NJ <http://www.merck.com/mrkshared/mmanual/section15/chapter188/188d.jsp> Spanos, NP (1994) Multiple identity enactments and multiple personality disorder: A sociocognitive perspective. Psychological Bulletin 116(1): 143-165. • To-be-forgotten words were in fact forgotten when patients switched states regardless of emotional valence. To-be-remembered words were also lost across states, but to a lesser degree. • This study is inconclusive because of the small sample size and lack of control subjects. • The jump in the graph for patients indicates that whatever was learned in the first state was lost in the switch to the second. • However, the identical jump in the simulators makes it unclear if the patients truly forgot what was learned or were also simulating amnesia. • Procedures vary considerably between studies, so 3 representative papers are presented here that each employ different procedures and memory tasks.