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The Basics of the Human Memory System
Ever wondered why a child never touches a hot object after he/she has been burnt by it once? Also, why is a child scared of sitting on a swing, after it has fallen from it once? It is because human beings learn from past experiences, as also from the experiences of others. This is only possible because we have the capability of storing and retaining our experiences, knowledge, and also the vast amount of information that reaches us through our five senses of sight, hearing, touch, smell, and taste. This unique storage and retention capability in humans is called memory. Memory is absolutely critical to our ability to learning new things and also to act in a consistent manner. In order to understand the human memory, we would need to break it down into parts.
What is Memory
In today’s world most of us understand computers and thus we will try to understand memory by comparing it with the computer. There is no physical thing called as memory in the human body. Memory, in psychology, is explained as the process to encode, store and retrieve information. Memory is thus dependent on three processes, which are as follows: -
- Registration or encoding – Input of information into memory through the senses.
- Storage – the retention of information by creating a record of the information.
- Retrieval – the recovery, recall or recollection of the stored information.
Forms of Memory
Psychology has been able to distinguish between three forms of memory: -
- Sensory memory or Ultra short-term memory.
- Short-term memory; also referred to as working memory.
- Long-term memory.
Each sensory organ in our body has a memory in which the data received from the outside world is stored for an ultra short duration. This store has duration of up to two seconds (depending on the sense) and is used as a buffer, giving us time to attend to sensory input. This data is lost if attention is not paid to it during this ultra short duration. Since we have limited ‘attention’ resources, a lot of this data is lost in our day to day living. As an example, most of us have experienced looking at a wedding photograph and exclaiming, ‘oh, I did not realise that ‘x’ was also at the wedding’, when you see the person standing right next to you in a group photograph. The sensory organs pick up a lot of information but the brain does not have the processing capability to process all of it, and thus most of it that is not paid attention to is thus lost. Two of the important sensory mechanisms that we most often use during our life are discussed below.
- Sight – The memory associated with the eyes is called the iconic memory, which is capable of storing information for very short duration of about 0.5 to 1 second. The problem here is that as much as 10 million bits/ second of data travels down the optic nerve to the brain, but the brain has a limitation of processing on an average, only about 16 bits/ second; up to a maximum of about 40 bits/ second. Guess what happens to the rest of the information? Yes, it is lost forever, as the iconic memory cannot hold on to the data for long. The reason may be evident. The eye is being exposed to newer data every second, and would not be able to function without erasing the earlier data from the sensory store.
- Hearing – The sensory memory associated with sounds is called the echoic memory, which is capable of storing information for slightly longer than the iconic memory, about 2 – 7 seconds. It stands to reason because sound can be heard only once, and sense can be derived from the sound only once the following sound is heard. Imagine two situations – one, listening to a radio and two, reading a book. You would only understand the radio if you listen to the sounds in sequence – the sound is held unprocessed until the following sounds are heard and can lead to more meaningful data. However, a book can be re-read, over and over again to make sense.
Data or information from the sensory stores that is the focus of our attention is further received at the short term memory, which allows us to store this transitory information long enough to use it for our purposes. This memory can be compared to the RAM on the computer. It has a limited capacity and can thus get overloaded, and can hold information temporarily and for a specified duration only. Like in the case of the RAM, this memory is also called as the working memory. The limitation of this memory is that it can store only a relatively small amount of information at one time viz. 7 +/- 2 elements of information, for a short duration, typically for 10 to 20 seconds. These elements can be digits, letters, words, or other units. Latest research indicates that the category of elements have an impact on the number of chunks that can be remembered. However, the final number would be between 5 and 9. Try memorising a telephone number of 10 digits and you will find what a difficult task it is, if one does not chunk the numbers.
- Chunking - The capacity of the short term memory can be enhanced by splitting information in to ‘chunks’ (a group of related items). It is easier to remember 416-678-9234 than it is to remember 4166789234. In the first case, we have split the numbers into three chunks of 3 digits each, whereas in the second case we are talking of 10 elements, beyond our working memory capacity of 7 +/- 2, or a maximum of 9.
Pnemonics Another technique that is most frequently employed by us to better utilise our working memory and thus our ability to remember something is the use of mnemonics. In other words, it’s a memory technique to help your brain better encode and recall important information. It’s a simple shortcut that helps us associate the information we want to remember with an image, a sentence, or a word. The duration of the information stay in the working memory can be extended through rehearsal (mental repetition of the information) or encoding the information in some meaningful manner. Rehearsal or repetition increases the time the information can be kept in the short term memory by another 10 – 20 seconds, every time it is repeated. Popular mnemonic devices include acronyms, rhymes and chunking. An example of the first letter mnemonics for the five great lakes in North America is HOMES that represents lakes Huron, Ontario, Michigan, Erie and Superior.
Long Term Memory
The capacity of long-term memory appears to be unlimited. It is used to store information for the longer term as also for information that is not currently being used, including:
- Abilities, such as language comprehension.
- Knowledge of the physical world and objects within it and how these behave.
- Beliefs about people, social norms, values, etc.
- Motor programs, problem solving skills and plans for achieving various activities.
Long term memory can be compared to the hard drive in a computer. Like the computer hard drive, storage in long term memory is large; takes longer to retrieve; and needs neural links for retrieval of information. Forgetting with time does not mean that the information in long term memory is lost; it just implies that the neural link has become incapacitated due to non usage or other reasons. Information in long-term memory can be divided into three types
- Semantic - Semantic memory refers to our store of general, factual knowledge about the world, such as concepts, rules, one’s own language, etc. Semantic memory is not liable to change with time. It is also information that is not tied to where and when the knowledge was originally acquired. Fish lives in the water and a car has four wheels is part of information in the semantic memory. So also is our mother tongue.
- Episodic – Episodic memory is the name given by Enden Tulving in 1972, and is the memory of personal or autobiographical events (time, place, emotions, and contextual information). Tulving has seminally defined three key properties of episodic memory recollection. These are: “a subjective sense of time (or mental time travel), connection to the self, and autonoetic consciousness.” Autonoetic consciousness refers to a special kind of consciousness that accompanies the act of remembering which enables an individual to be aware of the self in a subjective time. We can usually place these things within a certain context. It is believed that episodic memory is heavily influenced by a person’s expectations of what should have happened, thus two people’s recollection of the same event can be drastically different. Episodic memory is subject to change with time and can trigger episodic learning. For example, having been burnt by fire once, a child is not likely to venture close to the fire again.
- Motor Programmes - If a task is performed often enough, it may eventually become automatic and the required skills and actions are stored in long term memory. These are known as motor programmes and are ingrained routines that have been established through practice. The use of a motor programme reduces the load on the central decision maker. It is a known fact that our brain can process one piece of information at a time. An often quoted example is that of driving a car: at first, each individual action such as gear changing is demanding and our conversation halts when we have to change gears, but eventually the separate actions are combined into a motor programme and can be performed with little or no awareness. These motor programmes allow us to carry out simultaneous activities, such as having a conversation whilst driving.
Psychology has divided the human memory into three parts – the sensory or ultra-short duration memory; the short term memory or the working memory and the long term memory. Each of these classifications has its own capabilities and limitations. Understanding our memory system would help us effectively use our memory system to the optimum by building on its strengths and overcoming its shortcomings.