There are three major systems of memory : Sensory Memory; Short-Term Memory (STM), and Long-Term Memory(LTM). Information moves successively through these three systems if attention is given to the material. If attention (focused awareness) is not given, information does not move further into the system.

(i) Sensory Memory: Hold any object about 12 inches in front of you. Look at it steadily for a while. Close your eyes and notice how long the clear image of that object lasts. A clear visual image of any object will last in sensory memory for about

half a second after the stimulus is removed. Sensory memory holds representations of sensory input for very brief periods of time, depending upon the modality involved. There are different sensory registers for each of the senses.

(ii) Short-Term Memory (STM): Look up for a moment and note what attracts your visual attention. Try to identify the sounds and sensations that you are experiencing now. What you have identified is the content of short-term memory or STM. It holds relatively small amounts of information for brief periods of time, usually 30 seconds or less. This is the memory system we use when we look up the phone number and dial it. If we are connected on the first instance the telephone number is forgotten. However, if we get the line engaged for some time, we keep on dialling the number and through repeated dialling rehearsal of the telephone number we push it to the long-term memory (LTM) storage. 

However, it has been found that short-term storage is more than a passive “holding area” (e.g. holding a telephone number). On the contrary, it involves active processing of information. This finding has led psychologists to use the term working memory. It means that something active goes on during the short-term memory. 

(iii) Long-Term Memory (LTM): It refers to the memory system for the retention of large amounts of information for long periods of time. It is the memory system that permits us to remember events that happened many years ago, yesterday, last year, and so on. It is the long-term memory that allows us to remember factual information making it possible for us to learn different subjects, appear for examinations and communicate with others. It brings continuity and meaning to our life. 

When we pay attention to a piece of information and engage in active rehearsal the material is stored in the long-term memory (LTM). Information in the sensory memory enters short-term memory when it becomes the focus of our attention. If we do not pay attention to the incoming sensory information, the material fades and quickly disappears. We tend to pay attention to certain information and not to the other. Paying attention to certain aspects of our world is what we call. “selective attention”. The information from STM is often rehearsed by us. This rehearsal helps the transfer of that information from STM to LTM.