Classification Schemes of Memory

As I wrote in a previous blog [1], I learned about a classification scheme of memory from the review [2] of a book [3]. I wanted to learn more about it. At a Web site [4] I have learned the following: There are three schemes of classification of memory, i.e., classification by duration, classification by information type and classification by temporal direction. The scheme I learned before is the first one, and it classifies long-term memory, the largest part of any model about memory, into declarative (explicit) and procedural (or non-declarative; implicit) memories.

The classification by information type deals only with the long-term memory. Then it is not a scheme independent of the classification by duration but the one that subdivides the latter. The explanation of the latter at the above Web site [4] is as follows:

Classification by Duration

A basic and generally accepted classification of memory is based on the duration of memory retention, and identifies three distinct types of memory: sensory memory, short-term memory, and long-term memory.

The classification by temporal direction is explained as follows:

Classification by Temporal Direction

A further major way to distinguish different memory functions is whether the content to be remembered is in the past, retrospective memory, or whether the content is to be remembered in the future, prospective memory. Thus, retrospective memory as a category includes semantic memory and episodic/autobiographical memory. In contrast, prospective memory is memory for future intentions, or 'remembering to remember' (Winograd, 1988). Prospective memory can be further broken down into event- and time-based prospective remembering. Time-based prospective memories are triggered by a time-cue, such as going to the doctor (action) at 4 pm (cue). Event-based prospective memories are intentions triggered by cues, such as remembering to post a letter (action) after seeing a mailbox (cue). Cues do not need to be related to the action (as the mailbox example is), and lists, sticky-notes, knotted handkerchiefs, or string around the finger are all examples of cues that are produced by people as a strategy to enhance prospective memory.

Can this classification be said to be the one at the same level with the classification by duration from a different viewpoint? Anyway I doubt that prospective memory is essentially different from retrospective memory. The former seems only to be the special case of the latter in which the retrospective content is a decision already made in the form of a schedule related to the future.

I also cite the description about declarative memory [4] below.

Declarative memory requires conscious recall, in that some conscious process must call back the information. It is sometimes called explicit memory, since it consists of information that is explicitly stored and retrieved.

Declarative memory can be further sub-divided into semantic memory, which concerns facts taken independent of context; and episodic memory, which concerns information specific to a particular context, such as a time and place. Semantic memory allows the encoding of abstract knowledge about the world, such as "Paris is the capital of France". Episodic memory, on the other hand, is used for more personal memories, such as the sensations, emotions, and personal associations of a particular place or time. Autobiographical memory - memory for particular events within one's own life - is generally viewed as either equivalent to, or a subset of, episodic memory. Visual memory is part of memory preserving some characteristics of our senses pertaining to visual experience. We are able to place in memory information that resembles objects, places, animals or people in sort of a mental image.

At first I thought that the word "information" used in the review [2] to explain the semantic memory seemed a little odd in the context. Considering the fact that classification of memory can be made by information type, however, the use of the word "information" is quite natural.

1. Speeding Up of Life at Higher Ages (May 4, 2005).
2. Y. Dudai, Nature Vol. 434, p. 823 (2005).
3. D. Draaisma, Why Life speeds Up As You Get Older: How Memory Shapes Our Past translated by A. & E. Pomerans (Cambridge University Press, 2004).
4. Memory - Learn all about Memory (Encyclopedia.lockergnome.com).