Memory is a vital part of human existence. It enables people to gain new necessary experience, keep their knowledge, and use the previously stored material if they need it. Psychologists define memory as the ability to encode, store, retain, and recall information, past experience, personal memories, or motor processes in the brain. The majority of people tend to think of memory as if it were just a single memory process. However, memory is actually the multifaceted and interlinked system, which includes several components such as sensory register, short-term (STM) and long-term memory (LTM) stores.
One of the main characteristics of memory is its multi-component nature. Psychologists R. Atkinson and R. Shiffrin extensively investigated this feature of memory and represented the model of memory as a chain of three stages, from sensory memory (SM) to STM, and then to LTM. Their theory is also known as the modal or multi-store model. Baddeley, Eysenck, & Anderson view the Atkinson-Richard model as a flow of information from the environment through a sensory store and a short-term store to LTM. Over last years, some underlying assumptions of the multi-store model have been questioned and criticized. Nevertheless, it remains one of the most famouse models for studying memory in psychology.
The first element of memory architecture is SM. It is the capability to hold impressions of sensory information after the effect of original stimuli ends. Its function is a sensual buffer for impulse received via the five senses: sight, hearing, taste, smell and touch. Scientists assume that there are different subtypes of SM for each of the five senses. Nevertheless, only three of these subtypes have been extensively investigated: iconic, echoic, and haptic memories. The first subtype, iconic memory, is the fast-decaying storage of information, perceived via sight. It provides a representation of the person’s visual perception of the world for a brief period. The second subtype is echoic memory that acts as the storage for aural stimuli. It is able to hold a large volume of auditory information but has a very short duration, namely from one to four seconds. The third subtype is haptic memory. It is a system of sensory memory that recollects the data acquired by touch after stimuli have appeared. Sensory receptors experience sensations like pressure or pain, which are kept in haptic memory less than a second before vanishing or being transported to STM. Scientists have only recently found evidence of haptic memory and therefore this form of SM is not extensively studied compared to iconic and echoic memories. The main types of SM relate to visual, auditory and tactile senses.
One of the main characteristics of SM is its extremely brief duration. It decays very quickly, typically it lasts approximately 200 - 500 milliseconds after the perception. Only some forms of SM can last a few seconds. Due to ultra-short duration of SM, people typically remain unaware of its functioning. However, SM manages to complete its mission in memorizing process and send information about an item to STM. The transportation of information from the SM into STM is performed via attention, which selects only those stimuli, which are of interest at any given time.
After passing SM, information flows to the next store – STM. It is the second component of the Atkinson-Richard model. STM is a form of memory that is in charge of remembering an insubstantial amount of information beyond the SM. It is able to keep data in mind in an available state for a brief time (from ten to fifteen seconds, or sometimes about a minute). Although STM has been investigated for many years, its nature, functioning, and structure remain unclear.
Some scientists view STM as a separate form of human memory. On the contrary, others define STM just as a part of LTM that is currently can be used. Regardless of which concept is more precise, there are key aspects of STM that distinguish it from LTM. The first feature of STM is its remarkably limited capacity. According to results of the George Miller’s well-known experiment, STM can store between five and nine elements at a time (seven + two). This statement is sometimes called as Miller's Law. The second key aspect of STM is acoustic encoding. STM is assumed to use mostly an acoustic code for storing data. It typically translates visual information into sounds. The third aspect is extremely brief duration of STM. It allows holding information for a few seconds, sometimes up to a minute without repetition. Thus, stored short-term memories disappear very rapidly. However, memories can be transferred to LTM with the help of repetitions.
The final stage of the Atkinson-Richard model of memory processing is LTM. Unlike two previous stages, sensory and short-term, LTM is believed to have few, if any, limitations in capacity or duration. One more difference between short- and long-term memories is the type of method that a person uses to retrieve the previously stored information. In order to get necessary data from STM, a person applies the item-by-item search strategy, while he or she rather uses a system of association or cues to detect needed memories in the long-term store. Furthermore, short- and long-term memories differ from one another in the coding of information. The semantic codes play a primary role in LTM, while acoustic ones are dominant in STM. SHM and LTM can be distinguished one from another because of their numerous differences.
LTM is divided into two main types: explicit and implicit memories. The first type, explicit memory (also called declarative memory), comprises the conscious recollection of memories such as events, facts, and locations. In addition, it has two subcategories: episodic and semantic memories. Episodic memories refer to specific things that a person has experienced such as times, or associated emotions while semantic memories relate to information of a factual nature, for instance, the meaning of words, understanding of mathematics. This type of memory is knowing facts about the world.
The second type, implicit or nondeclarative memories are the unconscious recollections of skills and abilities to do something, for example, knowledge how to play the piano, ride a bike, tie shoe-laces or jump on a trampoline. Psychologies distinguish three types of implicit memories: 1) classical conditioning that involves learning of a new behavior through the process of association; 2) procedural memories, which relates to knowledge of how to do things; 3) priming, the process when exposure to one stimulus effect the response to another stimulus. All these types compose a complex structure of memory.
To summarize, memory is the complex mental process that involves encoding, storing, retaining and recalling of information. Memory is believed to be the multi-structural and interconnected system, which consists of three main components: sensory, short- and long-term memories. Memorization of information consists in its transportation from the environment through sensory memory to STM, and finally to the LTM. These three types of memory differ from one another in their capacity, duration and in type of encoding or retrieving processes they primarily use. The first type, sensory memory has brief time of functioning, large volume and different sensory types. The next type, STM is assumed to have limited capacity and duration. Finally, the LTM has no limitation of capacity or duration.
