when the S appeared in a space that was previously unoccupied that
subjects’ performance—the speed with which they could name the global
letter—was impaired (Hillstrom & Yantis, 1994).
You can recognize this phenomenon as stimulus-driven capture, because it
works in the opposite direction of the perceiver’s goals. Because, that is, the
subjects would perform the task better if they ignored the small S, they must be
unable to ignore it (since subjects almost always prefer to perform as well as
possible on the tasks researchers assign them). The important general conclu-
sion is that your perceptual system is organized so that your attention is auto-
matically drawn to objects that are new to an environment.
The Fate of Unattended Information If you have selectively attended to some
subset of a perceptual display—by virtue of your own goals or of properties of
the stimuli—what is the fate of the information to which you did not attend?
Imagine listening to a lecture while people on both sides of you are engaged in
conversations. How are you able to keep track of the lecture? What do you no-
tice about the conversations? Could anything appear in the content of one or
the other conversation to divert your attention from the lecture?
This constellation of questions was first explored byDonald Broadbent(1958),
who conceived of the mind as acommunications channel—similar to a telephone
line or a computer link—that actively processes and transmits information.
Broadbent re-created the real-life situation of multiple sources of input in his
laboratory with a technique calleddichotic listening.
A subject wearing earphones listens to two tape-recorded messages
played at the same time—a different message is played into each ear. The
subject is instructed to repeat only one of the two messages to the experi-
menter, while ignoring whatever is presented to the other ear. This pro-
cedure is calledshadowingthe attended message (see figure 7.10).
Subjects in shadowing experiments remember the attended message and do
not remember the ignored message. Subjects usually do not even notice major
alterations in the ignored message, such as changing the language from English
to German or playing the tape backward. However, they do notice marked
physical changes as, for example, when the pitch is raised substantially by
changing the speaker’s voice from male to female (Cherry, 1953). Thus gross
physical features of the unattended message receive perceptual analysis, ap-
parently below the level of consciousness, but most meaning does not get
through.
According to Broadbent’s theory, as a communications channel the mind has
onlylimited capacityto carry out complete processing. This limit requires that
attention strictly regulate the flow of information from sensory input to con-
sciousness. Attention creates a bottleneck in the flow of information through
the cognitive system, filtering out some information and allowing other infor-
mation to continue. Thefilter theoryof attention asserted that the selection
occurs early on in the process, before the input’s meaning is accessed.
The strongest form of filter theory was challenged when it was discovered
that some subjects were perceiving things they would not have been able to if
150 Philip G. Zimbardo and Richard J. Gerrig