Capacity

Memory is the brains’s ability to store, retain, and subsequently retrieve information. Traditional studies of memory began in the realms of philosophy, including techniques of artificially enhancing the memory. The late nineteenth and early twentieth century put memory within the paradigms of cognitive psychology. In recent decades, it has become one of the principal pillars of a branch of science called cognitive neuroscience, an interdisciplinary link between cognitive psychology and neuroscience.

Sensory memory corresponds approximately to the initial period after an item is perceived. The ability to look at an item and remember what it looked like with just a second of observation is an example of sensory memory. With very short presentations, participants often report that they seem to observe more than they can actually report. In early experiments, subjects were presented with a grid of letters arranged into three rows. After a the brief presentation, subjects were then played a tone, cuing them for which of the rows to report. Based on these experiments, it was shown that the capacity of sensory memory was approximately 12 items, but that it degraded within a few hundred milliseconds. Because this form of memory degrades so quickly, participants would see the display but be unable to report all of the items. This type of memory cannot be prolonged via rehearsal.

Short term memory is believed to rely mostly on an acoustic code for storing information, and to a lesser extent a visual code. I has been found that test subjects have more difficulty recalling collections of words that are acoustically similar, such as dog, hog, fog, bog, log, etc. However, short term memory has been an unexplainable phenomenon with certain individuals gifted to remember large amounts of information quickly, and to be able to recall that information in seconds.

Long term memory can store much larger quantities of information for potentially unlimited duration, sometimes a whole life span. For example, given a random seven digit number, we may remember it for only a few seconds before forgetting, suggesting it was stored in our short term memory. On the other hand, we can remember telephone numbers for many years through repetition. This information is said to be stored in long term memory. While short term memory encodes information acoustically, long term memory encodes it semantically. It has been discovered that after 20 minutes, test subjects had the least difficulty recalling a collection of words that had similar meanings such as big, large, great, huge, etc.

Short term memory is supported by patterns of brain communication, dependent on regions of the frontal lobe. Long term memories are maintained by more stable and permanent changes in neural connections widely spread throughout the brain. The hippocampus is essential to the consolidation of information from short term to long term memory, although it does not seem to store information itself. Rather, it may be involved in changing neural connections for a period of three months or more after the initial learning.

One of the primary functions of sleep is improving consolidation of information, as it can be shown that memory depends on getting sufficient sleep between training and test, and that the hippocampus replays activity from the current day while sleeping.

The best way to improve memory seems to be to increase the supply of oxygen to the brain, which may be accomplished with exercise. Walking for three hours each week suffices, as does swimming or bicycle riding. One study found that frequent eating, such as five small meals a day, promotes a healthy memory by preventing dips in blood glucose, the primary energy source for the brain.

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