Q.What is the meaning of the terms 'encoding', 'storage' and 'retrieval'?

Memory is best understood not as a single act but as a process built out of three separate, though closely interrelated, stages: encoding, storage, and retrieval. Any piece of information a person ever remembers has necessarily passed through all three of these stages, and understanding each one separately is what allows psychologists to pin down exactly where a particular memory failure has occurred, rather than treating 'forgetting' as one vague, undifferentiated event.

Encoding is the first stage. It is the process through which information is initially recorded and registered so that it becomes usable by the memory system at all. Whenever a stimulus reaches our sense organs, it produces neural impulses, which are picked up in different areas of the brain for further processing. During encoding, this incoming information is received, some meaning is drawn out of it, and it is then represented internally in a form suitable for further processing and eventual storage. Encoding can happen at different levels of depth — a fact directly connected to the Levels of Processing view covered later in the chapter, where information encoded in terms of its meaning (semantically) tends to be retained far better than information encoded only in terms of its surface appearance or sound.

Storage is the second stage. Information that has already been encoded must also be retained and held over a period of time so that it remains available for later use — this holding process, whether it lasts a few seconds or an entire lifetime, is what storage refers to. Storage capacity and duration differ sharply across the three memory systems described later in the chapter: sensory memory holds a large amount of information for well under a second, short-term memory holds a small amount for around thirty seconds, and long-term memory is treated as an essentially permanent store of unlimited capacity.

Retrieval is the third stage. Information sitting in storage is only genuinely useful once a person is able to bring it back into conscious awareness so that it can be used to perform cognitive tasks such as problem-solving or decision-making. Retrieval, in other words, is the act of accessing stored information and making it available for active use.

Because memory consists of these three separate stages, it follows that memory failure is not a single kind of event — it can occur at any one of the three points. A person may fail to recall something because it was never encoded properly to begin with (an encoding failure), because storage was weak and the information was not adequately retained over time (a storage failure), or because the information was both encoded and stored correctly but the person simply could not access or retrieve it when it was needed (a retrieval failure). This last possibility — retrieval failure — turns out to be an especially important explanation for everyday forgetting, and is examined in detail later in the chapter under the causes of forgetting.