4.2 CHUNKS OF INFORMATIONIf you try to memorize a phone number, you will quickly realize that the
amount of information you can keep in short-term memory at any given time
is rather limited. A classical estimation of the number of items we can keep in
short-term memory is“seven, plus minus two”(Miller, 1956).^4 Given the
steady informationflow through this bottleneck, short-term memory can
process tremendous information over time. But if we have to keep too much
information in mind simultaneously, the bottleneck causes problems. When
performing an arithmetic calculation, or listening to a narrative, the difficulties
become obvious and various techniques are used to overcome it.
Whereas the distinction between short- and long-term memory corres-
ponds to the stages of acquiring and consolidating memories, the more
complex model ofworking memory(or working-with-memory) refers to the
simultaneous manipulation of items in memory, which can be both new or
previously learned (Schröger et al., 2004; Conway et al., 2009; Eichenbaum,
2012, pp. 351–79; Baddeley et al., 2015, pp. 67–98). There are competing
hypotheses of how working memory functions, the details of which are not
our concern in this chapter. The most important aspect of working memory is
that it combines information in different sensory modalities (such as vision,
touch, hearing, etc.). This process is coordinated by parts of the prefrontal
cortex. As the example of H.M. shows, working memory does not depend on
the hippocampus. For example, the“phonological loop,”suggested by Alan
Baddeley and Graham Hitch (1974; Baddeley et al., 2015, pp. 43–8) is assumed
to be specialized for holding sequences of acoustic or speech-based items.
A classical demonstration of the phonological loop is the difficulty of remem-
bering an alliterating set of words like“mad, can, man, mat, cap”after reading
the list aloud once, as opposed to remembering a random list such as“pit, day,
cow, pen, top,”or the list“big, wide, large, high, tall,”where words have
semantic but no phonological similarities. This observation supports the idea
that we heavily rely on how words sound when keeping them in working
memory, resulting in the confusion of words that sound similarly. The concept
of manipulating information in working memory is helpful in understanding
how the brain deals with the bottleneck mentioned above.
Let us come back to the example of the phone number. When you hear a
phone number and try to dial it or write it down, it is very difficult to keep it in
memory even for a short time. Also, new information that enters your brain—
such as a question asked by your conversation partner—tends to“push out”
previous information. There is a technique, however, that helps to overcome
(^4) More recently the number four has been suggested (Cowan et al., 2007).
Memory and Transmission 65