psychologist Arien Mack. On the basis of many experiments, he concluded that
‘we rarely see what we are looking at unless our attention is directed to it’ (2003,
p. 180).
In a typical experiment participants are asked to look at a screen and fixate a marker
(Mack and Rock, 1998). A cross briefly appears and they have to decide whether the
horizontal or vertical arm is longer. Then on a critical trial, an unexpected stimulus
appears – perhaps a black square or a coloured shape. Afterwards they are asked,
‘Did you see anything on the screen on this trial that had not been there on pre-
vious trials?’ On average 25% of participants say ‘no’. This was true even when the
cross they were attending to was slightly to one side of their fixation point and the
unexpected shape appeared on their fovea. Indeed, they were even less likely to
see the shape under these conditions (between 60% and 80% said they couldn’t
see it), suggesting that they had to actively inhibit attention at the fovea when
trying to attend somewhere else. Interestingly, if the unexpected stimulus was a
smiley face icon, or the person’s own name, they were much more likely to notice it,
suggesting that the unseen stimuli must still be processed to some extent.
A dramatic demonstration of inattentional blindness is the film starring ‘gorillas in
our midst’ (Simons and Chabris, 1999). Two teams of students are seen throwing
balls to each other, and observers are told to watch the white team very carefully
and count the number of passes made. Afterwards they are asked whether they saw
anything unusual in the film. What most usually miss is that a woman dressed in a
gorilla suit walks right into shot, turns to camera and thumps her chest, and walks
off on the opposite side. If you are an observer it is quite shocking to see the film
again and realise what you missed. In experiments, approximately 50% of observers
failed to notice the gorilla; they were more likely to see it when the counting task
was easier or when they were watching the black team (since the gorilla was black).
In a NASA experiment something similarly striking – and somewhat more
realistic – went unnoticed. Pilots were tested in a flight simulator and another
plane was placed on the runway as they simulated landing. Novice pilots were
more likely to see the obstruction, suggesting that the trained pilots failed to
see something so very unexpected. This fits with results showing that the most
important factor affecting inattentional blindness is a person’s own attentional
goals (Most et al., 2005). It is hard to see something that is truly unanticipated.
Attention may be necessary, but American psychologists Daniel Levin and
Daniel Simons (1997) wondered whether it is sufficient (see also Chapter 7).
In a change-blindness study they created short movies in which changes were
made during a cut, either in arbitrary locations or at the centre of attention. In
one movie two women are seen chatting over a meal. When the camera cuts to
a new position one woman’s scarf disappears, or the pink plates are changed
to white. Few observers noticed these central changes. In another film an actor
sitting at a desk gets up to answer the telephone and moves towards the door.
The camera then cuts to a view in the hallway where a different actor answers
the phone. When forty participants were asked to describe what they had
seen, only 33% mentioned the changed actor. Apparently, attending to the
main character in the film was not sufficient to detect the change. Levin and
Simons conclude that even when we attend to an object, we may not form a
rich representation that is preserved from one view to the next. So, although
