Quantitative Measurements of Autobiographical Memories A thesis submitted in partial fulfillment of the requirements for the degree of Master of Arts at George Mason University By

QUANTITATIVE MEASUREMENTS OF AUTOBIOGRAPHICAL MEMORIES Adam T. Vogel, MA George Mason University, 2008 Thesis Director: Dr. Giorgio Ascoli The scientific pursuit of the mind-brain relationship demands the ability to quantify subjective cognitive phenomena. I applied two new psychometric tools, called CRAM (Cued-Recalled Autobiographical Memories) test and SPAM (Spontaneous Probability of Autobiographical Memories), to probe the quantitative dimensions of autobiographical memories (AMs) in humans. In CRAM, a computer-based protocol first prompts the retrieval and temporary labeling of episodic memories by using word cues sampled from a word database with a frequency proportional to their natural language usage. Subjects then sequentially estimate when each event occurred and report the number of features for each of several elements (e.g. people, objects, location details, etc.) they can recall for every AM. This test has been also adapted for the web and is available at http://cramtest.info. Data collected from largely undergraduate participants (N = 191, M = 22 years old, SD = 7 years) confirmed classic results describing the temporal distribution of AMs as a steep, gender-independent power decay from the most recent episodes to childhood amnesia. Analysis further revealed a much more modest dependence of the total content of individual AMs on the episode age (M = 18.7 SE = 0.24 elements overall vs. M = 16.1 SE = 0.32 and M = 23.5 SE = 0.26 for the most remote and recent tenths of life, respectively). Contrasting among features, People and Episodes were found to be the least and most susceptible to temporal degradation (-33% vs -100% lifespan reduction), respectively. Elements of People and Context were found to be more independent of other features (i.e. possibly “primary”) for females than males, while the opposite held true for location and temporal elements. SPAM is a separate experiment that assesses the number of AMs recalled per unit of time by stochastically sampling, through an automated paging system, the probability to be reminiscing one’s past episodes, and the duration of these recalls. A first pool of volunteers (n = 48, Mdn = 21 y.o., MAD = 3 yrs.) retrieved, on average, 21 (SE = 2.65) AMs per waking hour. Combining all results enables rather detailed inferences, such as “during a typical day, 45 elements are recalled from the middle fifth of one’s lifespan”. Storage of age-specific population statistics in a large-scale informatics database will allow future queries of multi-dimensional frequency maps of human memories. Practical implications of both the data and the experimental design include improved diagnosis and monitoring of diseases such as Alzheimer’s and critical assessment of eyewitness reports. 1. AUTOBIOGRAPHICAL MEMORIES: Review and the State of the Art The scientific pursuit of cognitive phenomena strives to understand the mind beyond the qualitative descriptor, and into quantitative terms. Progress towards creating objective metrics of the mind has been extremely difficult and often times stalls on one particular aspect, curtailing true advancement. In this thesis I will introduce different concepts of memories, focusing on autobiographical memory (AM), as a cognitive phenomenon accurately depicted by the prior sentence. In the first chapter, a quick taxonomy of memory is given followed by a literature review of the different methods used to study aspects, or an aspect, or AMs. The current status of results are discussed in the second part of chapter 1 with a focus on the temporal distribution of AMs. Chapter 2 presents the goals of the proposed studies which are described in chapter 3. In chapter 4, preliminary results of the temporal distribution, quantitative content and frequency of AMs are given. Conclusions and further development of the experiments are concluded in chapter 5. 1.1 Definitions and Taxonomy of Memories A long established doctrine widely accepted in memory research is the distinction between short-term (STM) and long-term memories (LTM). Demonstrated in several 1 neuropsychological studies, the ability of amnesiacs to perform well on STM tasks while being completely incapable at LTM tasks outlines a physical separation of memory organization in the human brain (Baddeley & Warrington, 1970; Bayley, Hopkins, & Squire, 2006; Knowlton, Musen, & Squire, 1993; Remondes & Schuman, 2004). STM, also known as working memory, is defined by the ability to consciously hold information for a temporal period of approximately 20 seconds. Miller (1956) had a very large impact on the theory of information processing (i.e. working memory) that has bled out into the mainstream population with the proposal that humans can cognitively maintain and manipulate 7 numbers (± 2). Updated by Nelson Cowan, it is now currently considered that an adult can use mnemonic strategies to retain about 7 unique items, however, in absence of a memory strategy the mind can concurrently hold only approximately 4 separate, simple items (Cowan, in press). Short-term conceptually transitions onto long-term memories once the memory extends beyond 30 seconds. LTMs are categorized as either declarative (i.e., explicit) or non-declarative (i.e., implicit). The major distinction between these two categories emphasizes the notion of conscious recollection, where in, declarative memories are conscious recollections of events or facts (e.g., recalling the last time you went swimming) and non-declarative memories are characterized by various forms of unconscious memory (e.g., how to type at a keyboard). Declarative memory can be further subdivided into episodic and semantic memory. Episodic memories are recollections of spatially and temporally specific events while semantic memories refer to