Human Memory

Encoding is the process by which information is first recorded and registered so that it becomes usable by the memory system. Storage is the process of retaining and holding that encoded information over a period of time. Retrieval is the process of bringing stored information back into awareness so that it can be used for thinking, problem solving, or decision-making.

According to the stage model, information passes through three memory systems:

- Sensory memory: Incoming information first enters sensory memory. It has a large capacity but a very short duration of less than a second. It registers information from the senses as an exact replica of the stimulus.
- Short-term memory (STM): Information that is attended to enters STM. STM holds a small amount of information for a brief period, usually 30 seconds or less. Information in STM is mainly encoded acoustically and may be lost if it is not rehearsed.
- Long-term memory (LTM): Information that survives the limitations of STM enters LTM. LTM has a vast capacity and is a permanent storehouse. Information in LTM is encoded semantically, that is, in terms of meaning.

So, information moves from sensory memory to STM through selective attention, and from STM to LTM through maintenance rehearsal and especially elaborative rehearsal.

Maintenance rehearsal and elaborative rehearsal differ in the way they help information stay in memory:

- Maintenance rehearsal keeps information in STM by simple repetition, either silent or vocal. It only maintains the information for as long as repetition continues.
- Elaborative rehearsal helps information enter LTM by connecting new information with existing knowledge. It involves analysis, organisation, associations, linking to similar memories, and creating mental images.

So, maintenance rehearsal is based on repetition, while elaborative rehearsal is based on meaningful association and organisation.

Declarative memory and procedural memory are two major types of long-term memory:

- Declarative memory contains facts, names, dates, and information that can be stated verbally. For example, remembering that India became independent on 15 August 1947 or that a frog is an amphibian.
- Procedural memory refers to memory for procedures, skills, and how to do things, such as riding a bicycle, making tea, or playing basketball. Its contents are not easily described in words.

Thus, declarative memory is memory for knowing what, while procedural memory is memory for knowing how.