Hermann Ebbinghaus was the leader in the study of memory. In 1885 he published a book called Über das Gedachtung.
There are three processes of memory which include encoding, storage, and retrieval.
According to the Stage Model, there are 3 stages of Memory: Sensory Memory, Short-Term Memory, and Long-Term Memory.
Sensory Memory lasts about .25-3 seconds.
Short-Term Memory lasts about 20 seconds.
And Long-Term is thought to be permanent.