Memory (II)
Even if showing the importance of organization, these studies nonetheless rely in the same old method of learning strings of isolated words. Recently, however, other type of studies has been initiated that attempt to clarify the storage of more complex material such as pictorial scenes. The theoretical analysis of results still remains difficult.
A special memory system that is of interest to cognitive psychologists is the one known as semantic memory. This system is where the individual's knowledge of the world is stored. It is called 'semantic' because it is a requisite to the comprehension of a language that, in addition of the words of that language, a person know the characteristics of the world that the language describes.
The opposite to remembering is forgetting. Forgetting can occur because the information is no longer stored or because it is not retrievable. A great amount of information is eliminated within short time of being acquired, principally trivial details that would soon clutter the individual's memory. Forgetting may be increased by the existence of similar information, specially when it is abundant, independently of the moment of learning. This feature is known as interference.
The elimination of detail that seems to be non-essential is of particular importance in the recall of events. People tend to remember what they think is more important. Later, when recalling, they attempt to reconstruct the event using the remaining information. The result is that they may recall what would have been occurred, rather than what actually occurred.
A theory about forgetting was proposed by Sigmund Freud, who argued that forgetting is, in reality, repressing incidents that the person associates with feelings of anxiety. This theory, however, has little experimental evidence. It is probable that memory traces in the brain suffer spontaneous decay that produces the consequent loss of information.
The existence of memory traces in brain was demonstrated in the case of a lower-level animal known as 'Aplysia californica' or sea slug. Experiments carried over a 30-year period showed the development of a typical stimulus-response conditioning with effects on the neuronal structure of the animals' brains. The brain of a sea slug consists of only about 20,000 neurons and so the researchers were able to find the groups of neurons that were producing neurotransmitters, and the new nerve connections that had grown, in response to the stimuli.
Experiments have also been performed with more advanced animals, and with embryonic and developing brains. A theory has been proposed, called 'neural darwinism,' that connections among cells that process sensory information are strengthened while other cells die off. The early idea that memories could be located in specific locations of the brain is being abandoned in favor of the idea that the brain alters the structure of its interconnections to accommodate new memories.
The existence of different parts of the brain that give support to different types of memory functions has been demonstrated by cases of subjects with partial brain damage. These subjects may show poor short-term memory and normal long-term memory. The inverse can also happen. Of course, it cannot be ascertained in either case if the trouble is a learning or a retrieval failure.
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