96 • CHAPTER 4 Attention
● FIGURE 4.18 Frame from the fi lm shown by Simons and
Chablis in which a person in a gorilla suit walked through the
“basketball” game. (Source: D. J. Simons & C. F. Chabris, “Gorillas in Our Midst:
Sustained Inattentional Blindness for Dynamic Events,” Perception, 28, 1059–1074,- Figure provided by Daniel Simons.)
horizontal arms apparently made observers “blind” to the
unattended test object. This effect is called inattentional
blindness.
Mack and Rock demonstrated inattentional blind-
ness using rapidly fl ashed geometric test stimuli. But other
research has shown that similar effects can be achieved using
more naturalistic stimuli that are presented for longer peri-
ods of time. Imagine looking at a display in a department
store window. When you focus your attention on the display,
you will probably fail to notice the refl ections on the surface
of the window. Shift your attention to the refl ections, and
you become less aware of the display inside the window.
Daniel Simons and Christopher Chabris (1999) created
a situation like the department store window, in which one
part of a scene is attended and the other is not. They created
a 75-second fi lm that showed two teams of three players
each. The team that was dressed in white was passing a
basketball around, and the other, dressed in black, was not
handling the ball. Observers were told to count the number
of passes, a task that focused their attention on the team in
white. After about 45 seconds, an event that took 5 seconds
occurred. One of these events was a person dressed in a
gorilla suit, walking through the scene (● Figure 4.18).
After seeing the video, observers were asked whether
they had seen anything unusual happen or whether they
had seen anything other than the six players. Nearly half—46 percent—of the observers
failed to report having seen the event, even though it was clearly visible. These experi-
ments demonstrate that when observers are attending to one sequence of events, they
can fail to notice another event, even when it is right in front of them (also see Goldstein
& Fink, 1981; Neisser & Becklen, 1975).CHANGE DETECTION
Following in the footsteps of the experiments in which observers were given a distract-
ing task, researchers developed another way to demonstrate how a lack of attention
can affect perception. Instead of presenting a task that
distracted attention from a test stimulus, they presented
fi rst one picture, then another slightly different picture,
and asked observers to indicate whether they saw any dif-
ference between the two pictures. To appreciate how this
works, try the following demonstration.DEMONSTRATION Change Detection
Look at the picture on the left (● Figure 4.19) for just a moment;
then cover the picture and see whether you can determine what
is diff erent in ● Figure 4.20. If you don’t see the diff erence,
repeat the procedure. Do this now, before reading further.Were you able to see what was different in the second
picture? People often have trouble detecting the change
even though it is obvious when you know where to look.
(Try again, paying attention to the sign near the lower left
portion of the picture.) Ronald Rensink and coworkers
(1997) did a similar experiment in which they presentedChange Detection
● FIGURE 4.19 Look at this picture for about a second, cover it,
and look at Figure 4.20 (at the top of the next page).Bruce GoldsteinCopyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.