The study of human memory since ages has been a topic of interest for the school of cognitive psychology. Human memories of all individuals can never be same. Human memory refers to a process of acquisition, storage, retention and retrieval of information. Human memory has the ability to store and recall the previously learnt information, but the functions performed by human memory may not be free from flaws because of forgetfulness or other memory disorders. Memory disorders resulting from diseases can affect the quality of life and the overall cognitive abilities of an individual.

In Psychology, Human memory follows three stages:

1. Encoding (Registration) stage: This is the first stage of human memory which is about processing the information which is received and collating the same. It is with the process of encoding, human brain receives the information from the external world through sensory organs which are transmitted in the form of physical and chemical stimuli. During this stage, the information is changes into a usable or a meaningful form.
2. Storing: In this second stage, information is stored in the human memory for a very long period of time. A permanent record of information is created in the human memory as a result of encoding.
3. Retrieval (Recalling or Recognizing): In this stage, information can be recalled or retrieved as per the requirement of the situation or in response to a given cue. The stored information is recalled or extracted into our conscious awareness.

Problems may take place in any stage of this process. Distractions hamper the process of encoding or extraction of information from the external world. Issues may take place even during the stages of storage and retrieval.

Human memories can either last for a very brief period, may be just for few seconds, or may last for a short term period, while some memories last for a very long time period may be weeks, months or even several years altogether, which usually remain out of our conscious level of awareness and can be brought back to the conscious awareness whenever required.

The encoded information can be put to a meaningful use by passing through a process of retrieval. Factors which influence the retrieval process of memory are types of information which is being used and the cues which are available for retrieving the information.

The Stage Model of memory as propounded by Atkinson and Shiffrin in 1968

The stage model of memory is considered to be the major study which attempts to explain the functioning of human memory. This theory demarcates three different stages of human memory: sensory memory, short term and long term memory.

1. Sensory Memory: This is the first stages of memory that stores the information extracted from the external environment for a very brief period of time, approximately for less than a second for visual information and for 3 to 4 seconds in case of auditory information. Sensory memory cannot be controlled by our conscious awareness and is not involved in our higher level cognitive functions.
2. Short-Term Memory: This is also called Active Memory, as it deals with the information which is fresh on our mind, about which we are currently thinking and have awareness. As per the Freudian Psychology, this kind of memory is referred to as conscious mind.

   The memory stored in the Short Term Memory (STM) will stay for approximately 20 to 30 seconds and then it moves on to the next stage that is Long Term Memory if not forgotten. Short Term Memory is capable of holding only few items and that too for a very brief period of time.

   The information or the items can be moved from the Short Term Memory to Long Term Memory via a process which is called rehearsal.

   Example of rehearsal could be when someone shares the phone number and you and you keep repeating it to yourself until you find something suitable to note it down somewhere. During this period, if someone interrupts by asking some question while you are rehearsing, you might forget the number because it was held in the STM.

3. Long Term Memory: As per the Freudian Psychology, Long term Memory is related to unconscious or preconscious. In this stage, the information storage process takes place on a continuous basis.

   The information which is stored in the Long Term Memory (LTM), usually remain out of our awareness, but can be recalled back to the working memory whenever needed. Long Term Memories have an incredible storage capacity like some memories remain stored in our mind for our entire lifetime from the time it was created.

   Long Term Memory can be of various types:

   • Declarative or Explicit Memory: This kind of memory is stored in the conscious mind and will require a conscious recall.

     Explicit memory is further categorized into semantic memory (For example, the capital of France is Paris, which is contextual information) and episodic memory which is in the form of personal experiences (example: I could see Monalisa, while being in Paris).

   • Procedural/Implicit Memory: Procedural or implicit memory is not based on conscious storage of information or information retrieval, but it is implicit in nature.

     This kind of memory is put to use for acquiring new motor skills. Some of the examples of implicit memory are learning bike riding, as one does not remember consciously how to ride a bike, but it happens on its own.

How Memory Organizes the Information?

Memory organizes related information in grouped by way of a process called as clustering.

Clustering involves categorization or grouping of information which is quite similar in nature, as it facilitates convenience in retrieval as well as recall of the information.

Another method by way of which information can be organized and recalled is semantic network model. As per this model certain experiences trigger our previous associated or related memories. The sight of a specific location might trigger the past memories which must have been associated or related with that location.