Supposedly, humans are able to hold 7 plus or minus 2 items in memory. This
number is based on George
Miller's (1956) work on digit span recall
tasks. In particular, Miller examined how people encode and recall
lists of increasingly difficult digit sequences. He found that
people were generally only able to recall between 5 and 9 "chunks"
of information (even when given other types of material to study,
e.g. words). He concluded that the human memory system has a capacity
of 7 plus or minus 2 chunks.