The Human Memory - what it is, how it works and how it can go wrong
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The Human Memory - what it is, how it works and how it can go wrong
INTRODUCTION
TYPES OF MEMORY
MEMORY PROCESSES
MEMORY DISORDERS
MEMORY & THE BRAIN
SOURCES & REFERENCES

Introduction
  The Human Memory
  What Is Memory?
  The Study of Human Memory


THE STUDY OF HUMAN MEMORY

??? Did You Know ???
Proponents of the “tabula rasa” (blank slate) thesis favour the nurture side of the nature versus nurture debate, when it comes to aspects of personality, intelligence and social and emotional behaviour.
The idea first surfaced in a treatise of Aristotle, but then lay dormant for over a thousand years until developed by the 11th Century Persian philosopher Avicenna, and then John Locke’s classic statement of the theory in the 17th Century.
Sigmund Freud revived the idea in the 20th Century, depicting personality traits as being formed by family dynamics.
The study of human memory stretches back at least 2,000 years to Aristotle’s early attempts to understand memory in his treatise “On the Soul”. In this, he compared the human mind to a blank slate and theorized that all humans are born free of any knowledge and are merely the sum of their experiences. Aristotle compared memory to making impressions in wax, sometimes referred to as the "storehouse metaphor", a theory of memory which held sway for many centuries.

In antiquity, it was generally assumed that there were two sorts of memory: the “natural memory” (the inborn one that everyone uses every day) and the “artificial memory” (trained through learning and practice of a variety of mnemonic techniques, resulting in feats of memory that are quite extraordinary or impossible to carry out using the natural memory alone). Roman rhetoricians such as Cicero and Quintillian expanded on the art of memory or the method of loci (a method often first attributed to Simonides of Creos or the Pythagoreans), and their ideas were passed down to the medieval Scholastics and later scholars of the Renaissance like Matteo Ricci and Giordano Bruno.

The 18th Century English philosopher David Hartley was the first to hypothesize that memories were encoded through hidden motions in the nervous system, although his physical theory for the process was rudimentary at best. William James in America and Wilhelm Wundt in Germany, both considered among the founding fathers of modern psychology, both carried out some early basic research into how the human memory functions in the 1870s and 1880s (James hypothesized the idea of neural plasticity many years before it was demonstrated). In 1881, Théodule-Armand Ribot proposed what became known as Ribot's Law, which states that amnesia has a time-gradient in that recent memories are more likely to be lost than the more remote memories (although in practice this is actually not always the case).

However, it was not until the mid-1880s that the young German philosopher Herman Ebbinghaus developed the first scientific approach to studying memory. He did experiments using lists of nonsense syllables, and then associating them with meaningful words, and some of his findings from this work (such as the concepts of the learning curve and forgetting curve, and his classification of the three distinct types of memory: sensory, short-term and long-term) remain relevant to this day.

The German evolutionary biologist Richard Semon first proposed in 1904 the idea that experience leaves a physical trace, which he called an engram, on specific webs of neurons in the brain. The British psychologist Sir Frederick Bartlett is considered one of the founding fathers of cognitive psychology, and his research in the 1930s into the recall of stories greatly influenced later ideas on how the brain stores memories.

??? Did You Know ???
Flashbacks are involuntary (and often recurring) memories, in which an individual has a sudden powerful re-experiencing of a past memory, sometimes so intense that the person “re-lives” the experience, unable to fully recognize it as a memory and not something that is really happening.
Such involuntary memories are often of traumatic events or highly-charged emotional happenings, and often occur at times of high stress or food deprivation, although the exact causes and mechanisms are not clear.
With advances in technology in the 1940s, the field of neuropsychology emerged and with it a biological basis for theories of encoding. Karl Lashley devoted 25 years of his life to research on rats in mazes, in a systematic attempt to pinpoint where memory traces or engrams are formed in the brain, only to conclude in 1950 that memories are not localized to one part of the brain at all, but are widely distributed throughout the cortex, and that, if certain parts of the brain are damaged, other parts of the brain may take on the role of the damaged portion.

The Canadian neurosurgeon Wilder Penfield’s work on the stimulation of the brain with electrical probes in the 1940s and 1950s, initially in search of the causes of epilepsy, allowed him to create maps of the sensory and motor cortices of the brain that are still used today, practically unaltered. He was also able to summon up memories or flashbacks (some of which the patients had no conscious recollection of) by probing parts of the temporal lobe of the brain.

As early as 1949, another Canadian, Donald Hebb, intuited that “neurons that fire together, wire together”, implying that the encoding of memories occurred as connections between neurons were established through repeated use. This theoretical idea, sometimes referred to as Hebb’s Rule, was supported by the discovery of the mechanics of memory consolidation, long-term potentiation and neural plasticity in the 1970s, and remains the reigning theory today. Eric Kandel’s work on sea-slugs (whose brains are relatively simple and contain relatively large, and easily-observed, individual neural cells) was particularly important in experimentally demonstrating Hebb’s Rule and identifying the molecular changes during learning, and the neurotransmitters involved.

As computer technology developed in the 1950s and 1960s, parallels between computer and brain processes became apparent, leading to advances in the understanding of the encoding, storage and retrieval processes of memory. The computer metaphor is, however, essentially just a more sophisticated version of the earlier storehouse view of memory, based on the rather simplistic and misleading assumption that a memory is just a simple copy of the original experience.

??? Did You Know ???
The brain in general, and memory in particular, has a distinct negativity bias. It pays more attention to, and highlights, unpleasant experiences.
The brain typically detects negative information faster than positive information, and the hippocampus specifically flags negative events to make doubly sure that such events are stored in memory.
Negative experiences leave an indelible trace in the memory, even when efforts are made to "unlearn" them.
This is probably an evolutionary adaptation, given that it is better to err on the side of caution and ignore a few pleasant experiences than to overlook a negative, and possibly dangerous, event.
The change in the overall study of memory during the 1950s and 1960s has come to be known as the “cognitive revolution”, and led to several new theories on how to view memory, and yielded influential books by George Miller, Eugene Galanter, Karl Pribram, George Sperling and Ulric Neisser. In 1956, George Miller produced his influential paper on short-term memory and his assessment that our short-term memory is limited to what he called “the magical number seven, plus or minus two”.

In 1968, Richard Atkinson and Richard Shiffrin first described their modal, or multi-store, model of memory - consisting of a sensory memory, a short-term memory and a long-term memory - which became the most popular model for studying memory for many years. Fergus Craik and Robert Lockhart offered an alternative model, known as the levels-of-processing model, in 1972. In 1974, Alan Baddeley and Graham Hitch proposed their model of working memory, which consists of the central executive, visuo-spatial sketchpad and phonological loop as a method of encoding.

The 1970s also saw the early work of Elizabeth Loftus, who carried out her influential research on the misinformation effect, memory biases and the nature of false memories. The pioneering research on human memory by Endel Tulving from the 1970s onwards has likewise been highly influential. He was the first to propose two distinct kinds of long-term memory, episodic and semantic, in 1972 and he also devised the encoding specificity principle in 1983.

During the 1980s and 1990s, several formal models of memory were developed that can be run as computer simulations, including the Search of Associative Memory (SAM) model proposed by Jerome Raaijmaker and Richard Shiffrin in 1981, the Parallel Distributed Processing (PDP) model of James McClelland, David Rumelhart and Geoffrey Hinton's in 1986, and various versions of the Adaptive Control of Thought (ACT) model developed by John Anderson in 1993.

Nowadays, the study of human memory is considered part of the disciplines of cognitive psychology and neuroscience, and the interdisciplinary link between the two which is known as cognitive neuroscience.

 
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