Memory and forgetting are intimately entwined. To fully understand memory, one must also understand the mechanisms that underlie forgetting, the loss of information or failure to recall previously learned material. As highlighted early in this text, forgetting is a common human affliction with benign and malignant implications. The text provides considerable scientific data for the adaptive function of forgetting, positing that without the pruning of old memories or the selective encoding of new information humans would be overwhelmed with trivia. This volume, one in a series about memory, culls together material from several fields. The contributors are an international group of experts representing several disciplines, including cognitive and behavioral neuroscience, experimental and cognitive psychology, neuropsychology, neuroimaging, neurobiology, and social psychology.
The book begins with an overview of preliminary considerations, including possible definitions of the term, etiological theories of forgetting, and a review of the classic memory processes of encoding, consolidation, and retrieval. Chapter 2 offers a succinct discussion of a possible evolutionary advantage of forgetting, to dissociate humans from stressful or life threatening events. Evidence supporting this premise is presented documenting states of psychogenic forgetting dating back to the mid-nineteenth century. Chapter 3 is of particular interest in that it offers a new taxonomy for the components of memory. The author provides a cogent argument for transitioning from Squire's (Reference Squire2007) dichotomous classification of declarative (episodic) versus non-declarative (implicit) to “reproductive” and “reconstructive” memory functions. Reproductive memory functions include facts and knowledge (analogous to Squire's concept of semantic memory) and procedures (e.g., riding a bicycle). The memory and learning involved in reproductive memory occurs after formal study, training, practice, or repetition. Reconstructive memory encompasses the recall of certain circumstances from our past (similar to episodic memory) and the ability to remember events or actions scheduled to occur in the future (prospective memory). As posited by the author, this new taxonomy allows for the distinction of different types of forgetting in normal and pathological states, and provides a useful framework to investigate forgetting specific to each memory component.
The next several chapters offer highly detailed discussions pertaining to the various proposed causes of forgetting with supporting empirical studies. Topics are broad and include mathematical models of forgetting curves and behavioral data that argue against failure to consolidate as a mechanism for forgetting as well as Hebbian error-correcting learning principles and other connectionist models of memory that support forgetting as the decaying of neuronal connections or as the result of overwriting with new information. Another chapter discusses cellular processes, which provide the neurobiological bases of implicit and explicit memory and forgetting. The chapter on neuroimaging covers data from fMRI studies, demonstrating the role of allocation of attention, or the lack thereof, in the disruption of consolidation. The role of sleep in memory formation and forgetting is also discussed. A careful read reveals that a general consensus of a unitary cause for forgetting remains lacking. Although this omission may be in part attributed to a more pronounced historical focus on the study of learning and memory as opposed to forgetting, the data presented argue for multiple mechanisms of the phenomenon of forgetting.
Of the theories presented throughout this text, forgetting as a function of various forms of interference has the most empirical support. Interference may be proactive or retroactive (these in essence reflect response competition) and the volume of material to be learned (greater forgetting occurs with increased amounts of information). Complementary theories that also have scientific support are those implicating the process of retrieval (competing or similar cues disrupt recollection) and reconsolidation (molecular alterations in memories with successive retrieval).
Although most of the material presented in this text is experimental and based on healthy adults, there are a few interesting chapters on pathological forgetting that have relevance for the practice of clinical neuropsychology. Several studies of patients with anterograde amnesia show that memory performance can be significantly enhanced when learning paradigms eliminate or delay retroactive interference. Some patients with anterograde amnesia maintain the ability to consolidate new information. Retention benefits over short and long durations have important treatment implications for patients. The chapter on accelerated long-term forgetting (ALF), a phenomenon in which forgetting occurs over extended periods disproportionate to normal performance on standard neuropsychological test delays, provides new insights into the role of the medial temporal lobes. Initially documented in temporal lobe epilepsy patients, ALF has been shown to impact verbal and visual but also remote autobiographical material. Although mixed findings have been reported, ALF appears partially attributable to subtle structural abnormalities in the medial temporal lobes thus suggesting that the hippocampus may play a greater role in prolonged memory consolidation. Clinical implications from studies of ALF may provide an explanation for discrepant subjective report of poor memory and unremarkable objective test results. In addition, ALF may be amenable to treatment.
The last few chapters in this volume focus on psychosocial forgetting such as psychogenic amnesia, autobiographical forgetting, and social forgetting. Neuroimaging data, based on case studies of patients with psychogenic amnesia, demonstrating dysregulation of the hippocampal formation and the ventral regions of prefrontal cortex suggest severe psychological distress alters brain functioning. Such evidence, as purported by the author, supports the notion that amnesias are likely to reflect a continuum between organic and psychological causation. Another chapter offers an intriguing discussion on the role of autobiographical remembering and forgetting which serve the function of maintaining our identity, including a coherent positive self image with memories that correspond with our internal reality. Moreover, autobiographic memory extends to social memory, and forgetting is at times goal directed and socially shared.
Forgetting is an extensive resource and a useful addition to the scientist's library. The field has come a long way since Ebbinghaus (Reference Ebbinghaus1885) first published his forgetting experiments. A variety of methodological advancements have aided our understanding of the mechanisms underlying this common phenomenon. The hope is that this knowledge will soon be used in the treatment of neurological or psychological memory dysfunction.
