There are also two classifications for long term memory, that is, secondary memory and tertiary memory.
Secondary memory is a large and stable storage system. The difference from the primary memory can be identified clearly depending on the type of mistake the memory makes when recalling. Primary memory makes mistakes of phonetic-similar sounds such as “p/ b”, and the secondary memory confuses words that are of similar meaning.
Another memory distinction is the time it takes to access. Primary memory recalls it quickly, and secondary memory more slowly. The loss of secondary memory retention seems to depend on the interference of the learning process during the learned knowledge. First a proactive inhibition and then a retroactive inhibition. Proactive inhibition is the more important factor because we have to control a large stock of learned knowledge. Therefore, this is the largest culprit of memory extinction.
The tertiary memory deals with engram, for example, one’s own name, skill to read and write or other practiced forms that are permanently retained from many years of practice, even if all other memory contents are lost somehow. The engram is also distinguished as having an extremely quick access time, as it is saved in a special memory form, the tertiary memory.
But a very good consolidated engram can also work with the secondary memory. The model of long-term memory corresponds to the secondary memory plus the tertiary memory.
花村嘉英（2005）「計算文学入門－Thomas Mannのイロニーはファジィ推論といえるのか？」より translated by Yoshihisa Hanamura