Developmental psychology.pdf

Memory 239
Images in the Sensjry System Immediately after we experience something, our
sensory system contains for a brief moment an image of the incoming information,
even after the stimulus has disappeared. The sensory register holds this momentary,
residual stimulation. The raw image remains in the sensory system, even though the
information has not been processed.
An impressive demonstration of the sensory register was accomplished when
adult subjects were shown three rows of a few letters each for a small fraction of a
second, and then they were asked to recall them. About half the letters were recalled
in this way, but the investigator hypothesized that virtually all of the letters had been
in the subjects' sensory register. The reason for the poor recall, it was hypothesized,
involved the delay between the appearance of the letters and the time required to recite
them (Figure 9.6).
To test this hypothesis the subjects were shown the same block of letters and
then by a special tone immediately after the stimulation was removed, they were asked
to recall one specific row within the block. The pitch of the tone as high, medium, or
low indicated that the first, second, or third row, respectively, was to be recalled. In
these instances the subjects were uniformly successful. They could recall any row in
the block of letters, which suggests that they had the whole pattern in mind after it
was withdrawn (Sperling, 1960).
M
N
P
R
К
X
Figure 9.6
Brief Visual Stimuli. Various
displays were used, all without
vowels to minimize the perception of
words (Sperling, 1960).
J
F
V
Images as Unprocessed Information The speed with which the sensory image
fades was also indicated in these experiments. When the signal for recall was delayed
by half a second or less, recall was significantly disrupted. When the delay was a full
second, the subjects' success was no greater than.it had been earlier, with no signal at
all. The image apparently remains for only a small fraction of a second (Sperling,
1960).
The sensory register contains only unprocessed information, which can be
transferred to the next stage, short-term memory, if the person chooses to do so. Have
you noticed, for example, that sometimes you can still remember a brief remark addressed
to you, even though you were not attending in the first place? You could process
it just a split second afterward because the words were still in the sensory register.
The fleeting visual image is called an icon, meaning a picture. If it is auditory,
it is called an echo, meaning something we still hear after the stimulus has disappeared.
Apparently there were images in Benjamin's auditory sensory register, for otherwise
there would have been no memory at all.
Short-Term Memory
If the image is to be remembered, it must be transferred to short-term memory (STM),
which is a stage of temporary storage, defined in most studies as any interval less than
30 seconds. During this period information is processed or ignored, and in the latter
case it never becomes a memory. In terms of the metaphor, short-term memory is a
receiving platform at the warehouse. This platform is limited in area, and the workers
have a limited time. Something must be done in a hurry, for another shipment will be
arriving soon.
Capacity for Short-Term Memory The limited capacity of short-term memory is
readily demonstrated in daily life. Ask an adult to repeat random series of single digits
with each series one digit longer than the previous one. Series of three, four, or five
digits are relatively easy, but nine or more are difficult or impossible. Telephone numbers
are appropriately seven digits, the average capacity for most adults, but for a child
like Benjamin Burtt, the span is much less.
This limited capacity of short-term memory was determined on an experimental
basis when adult learners were asked to memorize various amounts and types
of information. It was found that the average person could manage approximately seven
separate items. Highly successful people could manage up to nine categories, which