The visual cortex is a
fantastical portion of the brain, and one which is enlarged in our species to
the extent that we can use our eyes to make sense of the world around us in
amazing detail. We notice colours, shapes, motion, direction, and even three
dimensions, allowing the brain to generate a coherent percept of the visual
scene. Many primates like ourselves are extremely visual animals, and rely on
eyes not only to inform about the world around us, but to warn of impending
danger or alert about opportunity.
Despite
the amazing resolution and sophistication the visual system has, what could be
argued as one of its most interesting features is a mechanism of noise
filtration in which the brain effectively ignores irrelevant information it
receives, even resulting in features in the environment being completely
deleted from the scene a person sees. One of the most familiar examples of this
is that you can’t see your own nose when you look at a scene. The position of
the nose means it should take a commanding, even blocking position in the
visual field, and prevent us seeing objects in front of it. However, we never
see the dark shadow of our nose when we look around. This is because the brain
filters out the stimulus. Instead, it seems the scene is ‘filled in’ where the
nose should be with what the brain ‘expects’ to see- the nose is there all the
time, but rarely provides anything informative, so can usefully be ignored.
Another interesting way in which what we don’t see can
reveal more about how visual processing works than what we do see comes from
the phenomenon of ‘inattentional blindness’. One would imagine, that when a
person is concentrating intensely on a task which involves vision, that they
would be more observant. It seems, the opposite is the case, and they are in
fact much more likely to miss obvious features in a scene presented right in
front of their eyes. A famous example is what happens when subjects are shown a
video of a basketball match, and are asked to count the number of passes that
happen during a game sequence. During play, a person dressed in a gorilla
costume crosses the shot. When asked to report on what they saw, a 1999 study showed subjects could report the
number of passes observed, yet, incredibly did not report seeing the gorilla if
asked whether they noticed anything unusual about the video. In fact, people
appear flummoxed when they are told the gorilla featured, and are astounded when
they watch the video back, knowing that it will appear.
More recently, in a study (published 17th July,
2013) at Brigham and Women’s Hospital, researchers have probed the
‘inattentional blindness’ phenomenon further. It seems that even experts in a
field, when carrying out a routine task in their line of work, cannot notice
the obvious, or even the absurd!
In the investigation, 24 radiologists were asked to examine
scans of patients’ lungs and search for nodules which were perhaps indicative
of pathology (namely, carcinoma). They examined five scans with an average of
ten nodules each, and on the last scan, an image of a gorilla, 48 times larger
than the included nodules also appeared on the lung surface. Despite its
obvious presence, the great majority (83%) of radiologists tested did not
report seeing the gorilla.
Of course, it could be argued that this is down to
radiologists being over-worked, or highly stressed, or, simply, incompetent. This
is perhaps a ‘blinkered’ view of the situation, but one that must be considered.
Alternatively, and in my opinion, far more intriguingly, this study possibly
indicates something more eye-opening (excuse the pun!). Perhaps what we
perceive is a lot more influenced by what we are searching for, and what we
expect to see than we might think, and that, far from seeing an objective
representation of the world around us, the visual cortex unconsciously makes
decisions to include or exclude things in the environment that it regards as
more or less important to achieving a task. Even when an observer is
experienced, or even expert at a task, spotting what is obvious might be a
challenge for them, if it is very far from what they expect.
The idea that the brain lets us see a perhaps biased view of
reality, and we see only what we expect to see is perhaps a sinister one, but
it is perhaps a more potent mechanism of sensory noise filtration than was
thought. In evolutionary terms, it is a waste of energy to pay attention to
things which provide no relevant information, and so, more successful
individuals are those who can selectively filter stimuli which provide
information to enhance survival.
What is clear, is that being attentive certainly does not
equate to being observant. Further, no matter how experienced you are, and no
matter how hard you are concentrating, being unable to spot what is right in
front of you is harder than you might think! Perhaps, concentration and the
ability to observe the unexpected are negatively correlated. It might be useful
to ask whether those with attention deficit disorders, who are unable to focus
on a task, are more likely to notice the gorilla. This is entirely speculative,
but it is without doubt something worth investigating.
Citation: 'If you're not looking for it, you probably won't see it: Brigham and Women's Hospital study examines inattentional blindness in expert observers'- Press Release, 19th July 2013.
