store and manipulate the stored information depending on the task that they need to perform. For example, when you are required to solve a mathematical problem, the memory relating to mathematical operations, such as division or subtraction are carried out, activated and put to use, and receive the output (the problem solution). This analogy led to the development of the first model of memory, which was proposed by Atkinson and Shiffrin in . It is known as Stage Model .
M EMORY S YSTEMS : S ENSORY , S HORT - TERM AND L ONG - TERM M EMORIES According to the Stage Model, there are three memory systems : the Sensory Memory , the Short-term Memory and the Long-term Memory . Each of these systems have different features and perform different functions with respect to the sensory inputs (see Fig. . ).
Let us examine what these systems are: Fig. . : The Stage Model of Memory Information Sensory Memory Iconic (Sight) Echoic (Sound) and other senses Store Capacity - large Duration - less than one second Attention Short-term Memory Store Capacity - small Duration - less than seconds Elaborative Rehearsals Long-term Memory Permanent Store Capacity - unlimited Duration - upto a lifetime Sensory Memory The incoming information first enters the sensory memory . Sensory memory has a large capacity.
However, it is of very short duration, i.e. less than a second. It is a memory system that registers information from each of the senses with reasonable accuracy. Often this system is referred to as sensory memories or sensory registers because information from all the senses are registered here as exact replica of the stimulus.
If you have experienced visual after-images (the trail of light that stays after the bulb is switched off) or when you hear reverberations of a sound when the sound has ceased, then you are familiar with iconic (visual) or echoic (auditory) sensory registers. Short-term Memory You will perhaps agree that we do not attend to all the information that impinge on our senses. Information that is attended to enters the second memory store called the