According to its duration, memory formation is thought to follow a progression from a short-term unstable state, occurring immediately after learning, to a more stable and lasting state, which occurs with time after acquisition of new information. A continuum is formed between these two extremes, comprising different types of memory such as sensory memory, short-term memory, working memory and long-term memory. These memory stores are included within the “multi-store or multi-system” model of memory and differ from each other in terms of capacity limit and the length of time that information remains available to us.
Additionally, these types of memory are considered continuous processes that encompass distinct stages.
- Acquisition: learning.
- Consolidation: memory.
- Reconsolidation: the most recent process. Several neurobiological studies support its independence.
The distinction regarding the material included in the memory system has generally been based on the study of patients with specific brain lesions. In particular, patients with lesions in specific brain regions were found to have specific memory deficits. For example, patient J.P. had difficulty improving performance on tasks involving repetition and display of previously acquired skills, while other skills remained intact; in addition, J.P. was able to consciously recall past events. This memory specificity gave rise to another classification of memory based on the content of information which led to the division of long-term memory into two types: declarative or explicit memory and non-declarative or implicit memory.
Declarative or explicit memory
Declarative memory is responsible for codifying the information regarding biographical events and the knowledge of specific events. In this sense, explicit memory requires some effort to remember information that has previously occurred, also known as intentional recollection. Generally, this recall is usually motivated by some evocative stimulus that was present when the information was encoded, which facilitates recall. Declarative memory can be further subdivided into semantic memory, episodic memory and a special type of memory, recognition memory.
Non-declarative or implicit memory
On the other hand, implicit memory includes perceptual, motor and cognitive skills or abilities that have already been acquired and that can only be retrieved through action; individuals are unable to verbally “declare” these memories. In this case, memory is quantified in a different manner, specifically, it is argued that implicit learning is involved if there is an increase in performance in certain tasks.
Therefore, implicit memory refers to a change in behavior in the absence of conscious awareness of what has been learned. There are three general types of implicit memory: classical conditioning, priming, and procedural memory.
Overall, it is concluded that human memory is not a unitary, indivisible system but consists of several separate systems that differ in terms of duration, the content of the stored information and, in addition, the neural bases that support them.
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