When it comes to classification of memories, there are three main categories:
Sensory memory is first in this classification of memories and is our ability to remember certain aspects of information for less than a second after the stimulus has gone. Our sensory receptors have the ability to hold an enormous amount of information but everything held by these receptors only lasts for a fraction of a second. Sensory memory is divided into echoic and iconic memory.
Echoic memory refers to stimuli of an audio nature. Essentially, we are able to retain a mental echo for a few seconds after the stimulus was heard. An example of this is the ability to repeat words or numbers a few seconds after someone else has said them. Iconic memory is much more brief and lasts for just one quarter of a second. This relates to visual memory whereby we can remember items that have just flashed on a screen for a very short period of time.
Classification of memories continues with short-term memory which is the ability to hold a small amount of information for a few seconds. It is estimated that we can hold short-term memories for up to 20 seconds. George Miller came up with a theory that the human mind was capable of holding 7 plus or minus 2 pieces of information in its short-term memory store. He reached this conclusion from experiments in the 1960s. However, more recent studies have shown that the amount of information we can retain depends on a number of different factors and cannot be confined to a number between 5 and 9.
The process of chunking also puts a hole in Miller’s theory. Chunking enables you to recall information in groups which greatly increases your short-term memory capacity. For example, it is far easier to remember 3 groups of 4 rather than one group of 12 pieces of information. Also, the very nature of the information being recalled has a profound effect on how much we can remember.
Last in the general classification of memory is long-term memory. This form of memory is a stark contrast to the previous two because it can hold a seemingly unlimited amount of information for an unlimited length of time. Long-term memories could also be lifelong memories. One thing about long-term memory is the fact that we could forget information if it is not recalled at regular intervals.
Another factor crucial to long-term memory capacity is sleep. Lack of sleep can lead to a disorganized memory store. Although long-term memories can theoretically last a lifetime, there are various mental illnesses that can cause it to fade. Loss of memory actually occurs because the brain’s neuron store diminishes but illnesses like Dementia and Alzheimer’s can contribute to these lapses in memory. It is hoped that stem cell research can find ways to reverse the effects of these illnesses. The above is just a brief classification of memories as each type of memory can be broken down into several subcategories which in turn have their own separate sections.
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