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several information streams simultaneously. Effortful processingis encoding that requires
our attention and conscious effort.
Short-Term Memory
Short-term memory(STM) can hold a limited amount of information for about 30 sec-
onds unless it is processed further. Experiments by George Miller demonstrated that the
capacity of STM is approximately seven (plus or minus two) unrelated bits of information
at one time. STM lasts just long enough for us to input a seven-digit phone number after
looking it up in a telephone directory. Then the number disappears from our memory. How
can we get around these limitations of STM? We can hold our memory longer in STM if
we rehearsethe new information, consciously repeat it. The more time we spend learning
new information, the more we retain of it. Even after we’ve learned information, more
rehearsal increases our retention. The additional rehearsal is called overlearning. While
rehearsal is usually verbal, it can be visual or spatial. People with a photographic or eidetic
memory can “see” an image of something they are no longer looking at. We can increase
the capacity of STM by chunking,grouping information into meaningful units. A chunk
can be a word rather than individual letters, or a date rather than individual numbers,
for example.
Although working memory is often used as a synonym for STM, Alan Baddeley’s work-
ing memory model involves much more than chunking, rehearsal, and passive storage of
information. Baddeley’s working memory modelis an active three-part memory system
that temporarily holds information and consists of a phonological loop, visuospatial working
memory, and the central executive. The phonological loop briefly stores information about
language sounds with an acoustic code from sensory memory and a rehearsal function that
lets us repeat words in the loop. Visuospatial working memory briefly stores visual and
spatial information from sensory memory, including imagery,or mental pictures. The
central executive actively integrates information from the phonological loop, visuospatial
working memory, and long-term memory as we associate old and new information, solve
problems, and perform other cognitive tasks. Working memory accounts for our ability to
carry on a conversation (using the phonological loop), while exercising (using visuospatial
working memory) at the same time. Most of the information transferred into long-term
memory seems to be semantically encoded.
Cognition ❮ 129Figure 11.1 Atkinson–Shiffrin three-stage model of memory.