Psychology2016

232 CHAPTER 6

What you will discover is that most everyone you test will get past the first two

sequences of numbers, but some people will make errors on the six-digit span, about half of

the people you test will slip up on the seven-digit span, and very few will be able to get past

the nine-digit span without errors. This led Miller to conclude that the capacity of STM is

about seven items or pieces of information, plus or minus two items, or from five to nine bits

of information. Miller called this the magical number seven, plus or minus two. Since Mill-

er’s review of those early studies and subsequent conclusion about the capacity of STM being

about seven items, research methods have improved, as has our knowledge and understand-

ing of memory processes. Current research suggests younger adults can hold three to five

items of information at a time if a strategy of some type is not being used. When the informa-

tion is in the form of longer, similar- sounding, or unfamiliar words, however, that capacity

reduces until it is only about four items (Cowan, 2001; Cowan et al., 2005; Palva et al., 2010).

There is a way to “fool” STM into holding more information than is usual. (Think

of it as “stacking” related files on the desk.) If the bits of information are combined into

meaningful units, or chunks, more information can be held in STM. If someone were to

recode the last sequence of numbers as “654-789-3217,” for example, instead of 10 separate

bits of information, there would only be three “chunks” that read like a phone number.

This process of recoding or reorganizing the information is called chunking. Chances are

that anyone who can easily remember more than eight or nine digits in the digit-span test

is probably recoding the numbers into chunks. To see how well you do at remembering

numbers, participate in the Digit Span experiment Simulate the Experiment, Digit Span.

WHY DO YOU THINK THEY CALL IT “SHORT TERM”? How long is the “short” of short-

term memory? Research has shown that short-term memory lasts from about 12 to

30 seconds without rehearsal (Atkinson & Shiffrin, 1968; J. Brown, 1958; Peterson &

Peterson, 1959). After that, the memory seems to rapidly “decay” or disappear. In fact,

the findings of one study with mice suggest that in order to form new memories, old

memories must be “erased” by the formation of newly formed neurons (Kitamura

et al., 2009). The hippocampus only has so much storage room, and while many of the

memories formed there will be transferred to more permanent storage in other areas of

the brain, some memories, without rehearsal, will decay as new neurons (and newer

memories) are added to the already existing neural circuits.

What do you mean by rehearsal? How long can short-term

memories last if rehearsal is a factor?

Most people realize that saying something they want to remember over and over

again in their heads can help them remember it longer. We sometimes do this with names

we want to remember, or a phone number we want to remember long enough to enter

into our phone’s contacts. This is a process called maintenance rehearsal. With main-

tenance rehearsal, a person is simply continuing to pay attention to the information

to be held in memory, and since attention is how that information got into STM in the

first place, it works quite well (Atkinson & Shiffrin, 1968; Rundus, 1971). With this type

of rehearsal, information will stay in short-term memory until rehearsal stops. When

rehearsal stops, the memory rapidly decays and is forgotten. If anything interferes with

maintenance rehearsal, memories are also likely to be lost. For example, if someone is

trying to count items by reciting each number out loud while counting, and someone

else asks that person the time and interferes with the counting process, the person who is

counting will probably forget what the last number was and have to start all over again.

Short-term memory helps people keep track of things like counting.

Interference in STM can also happen if the amount of information to be held in

STM exceeds its capacity. Information already in STM may be “pushed out” to make

room for newer information. This is why it might be possible to remember the first few

maintenance rehearsal
practice of saying some information to
be remembered over and over in one’s
head in order to maintain it in short-
term memory.

This restaurant server is taking the woman’s
order without writing it down. Which
memory system is he using? Do you think
that his capacity for items in this system
may be greater than someone who does not
try to remember items like this often?