Q.Ravi keeps repeating a new phone number under his breath until he finishes dialling it, and then forgets it completely a minute later. Explain, using the concept of rehearsal, why Ravi's strategy fails to make the number a lasting memory, and describe what he could do differently.

The Stage Model of memory, proposed by Atkinson and Shiffrin in 1968, describes memory as a system of three separate stores through which information passes in sequence, borrowing its basic logic from how a computer registers, stores, and manipulates information. The three stores are sensory memory, short-term memory (STM), and long-term memory (LTM), and each has its own characteristic capacity and duration.

Information first enters sensory memory, which has a large capacity — able to register input from every sense — but an extremely short duration, with information decaying automatically in well under a second unless something is done with it. Sensory memory holds this information as a fairly exact replica of the original stimulus; the visual version is called iconic memory and the auditory version is called echoic memory, and everyday experiences like a lingering visual after-image or a fading echo of a sound illustrate these registers directly.

Only information that is actually attended to moves on from sensory memory into short-term memory. This is governed by the first control process, selective attention, which filters out the great majority of sensed information (which simply fades away unattended) and lets through only what is being actively focused on. STM holds a comparatively small amount of information — traditionally described as around seven items, plus or minus two — for a brief period, usually thirty seconds or less, and Atkinson and Shiffrin proposed that this information is mainly encoded acoustically, in terms of sound. Two further control processes operate within STM: maintenance rehearsal, which is simply repeating information (silently or aloud) to keep it available for as long as needed, though it is lost the moment the repetition stops; and chunking, which expands STM's effective capacity by combining several smaller units into larger, meaningful chunks — for example, breaking an overly long string of digits into recognisable groups, such as memorable years, so that the whole string becomes easier to hold in mind. …