Memory is the ability to retain information as mental impressions in the brain. Current concepts of memory accounted about four different kinds of memories: temporary, limited, volatile short term memory and permanent long-term memories. According to Olson (1985), memory does not act as a unitary whole rather it is a series of three separate entities viz. sensory register, short-term memory and long-term memory. Properties of different memories are tabulated below (Table 3).

 Table 3. Properties of different memories (Adapted from Olson, 1985)

Short-term sensory memory (STSM) serves as a momentary collection of sensory input. Human being has almost no control over sensory memory except to pay closer attention to an environtal channel according to expectation.

Short-term memory (STM) is poor for keeping large track of information and is more fragile/ volatile than long-term memory. Individual can control STM and can maintain information by grouping information, making items distinctive and rehearsing.

Long-term memory (LTM) is generally stored in semantic, visual, auditory and abstract formats.  LTM has large capacity and is virtually permanent. Human gains control over LTM by encoding information into rich meanings and linking items together and by being clever at finding items that appear to be lost (Olson, 1985).