86 • CHAPTER 4 Attention
This occurred because they were taking the mean-
ing of the words into account. (An example of
top-down processing! See page 52.) Because of
results such as these, Anne Treisman (1964) pro-
posed a modifi cation of Broadbent’s theory.
Treisman proposed that selection occurs in
two stages, and she replaced Broadbent’s fi lter
with an attenuator (● Figure 4.5). The attenuator
analyzes the incoming message in terms of (1)
its physical characteristics—whether it is high-
pitched or low-pitched, fast or slow; (2) its
language—how the message groups into syllables
or words; and (3) its meaning—how sequences
of words create meaningful phrases. Note that
this is similar to what Broadbent proposed, but in Treisman’s attenuation theory of
attention, language and meaning can also be used to separate the messages. Treisman
proposed, however, that the analysis of the message proceeds only as far as is neces-
sary to identify the attended message. For example, if there are two messages, one in a
male voice and one in a female voice, then analysis at the physical level is adequate to
separate the low-pitched male voice from the higher-pitched female voice. If, however,
the voices are similar, then it might be necessary to use meaning to separate the two
messages.
Once the attended and unattended messages have been identifi ed, both messages
are let through the attenuator, but the attended message emerges at full strength
and the unattended messages are attenuated—they are still present, but are weaker than
the attended message. Because at least some of the unattended message gets through the
attenuator, Treisman’s model has been called a “leaky fi lter” model.
The fi nal output of the system is determined in the second stage, when the message
is analyzed by the dictionary unit. The dictionary unit contains stored words, each of
which has a threshold for being activated (● Figure 4.6). A threshold is the smallest
signal strength that can barely be detected. Thus, a word with a low threshold might be
detected even when it is presented softly or is obscured by other words.
According to Treisman, words that are common or especially important, such as
the listener’s name, have low thresholds, so even a weak signal in the unat-
tended channel can activate that word, and we hear our name from across
the room. Uncommon words or words that are unimportant to the listener
have higher thresholds, so it takes the strong signal of the attended mes-
sage to activate these words. Thus, according to Treisman, the attended
message gets through, plus some parts of the weaker unattended message.
The research we have been describing so far was extremely important,
not only because it defi ned some of the important phenomena of atten-
tion, but also because it demonstrated how an aspect of cognition could be
conceptualized as a problem of information processing, in which the fl ow
of information from the environment is followed through various stages
of processing. Theories like Broadbent’s and Treisman’s are sometimes
called early selection theories of selective attention because they propose
a fi lter that operates at an early stage in the fl ow of information, in many
cases eliminating information based only on physical characteristics of the
stimulus.
Other theories were also proposed to take into account the results of
experiments that showed that messages can be selected at a later stage of
processing, based primarily on their meaning. For example, participants
in an experiment by Donald MacKay (1973) listened to ambiguous sen-
tences, such as “They were throwing stones at the bank,” that could be
taken more than one way. (In this example, “bank” can refer to a river-
bank or to a fi nancial institution.) These ambiguous sentences were pre-
sented to the attended ear, while biasing words were presented to the other,● FIGURE 4.6 The dictionary unit of Treisman’s
model contains words, each of which has a
threshold for being detected. This graph shows
the thresholds that might exist for three words.
The person’s name has a low threshold, so it will
be easily detected. The thresholds for the words
rutabaga and boat are higher, because they are
used less or are less important to this particular
listener.Own Rutabaga
nameLowHighSignal strength
needed to activateBoat● FIGURE 4.5 Flow diagram for Treisman’s attenuation model of selective
attention.Messages Attenuator Dictionaryunit To memoryAttended messageUnattended
messagesCopyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.