How did you decide on "somewhere around 7" concepts in thought at once? What counts as a "concept"? If you are referring to the 1956 George Miller paper "The Magical Number Seven, Plus or Minus Two", then that really has little to do with "concepts".

See Tufte: http://www.edwardtufte.com/bboard/q-and-a-fetch-msg?msg_id=0...

"That essay reviews psychological experiments that discovered people had a hard time remembering more than about 7 unrelated pieces of really dull data all at once."