VOL. 8, NO. 5, SEPTEMBER 1997
TO SEE OR NOT TO SEE:
The Need for Attention to Perceive Changes in Scenes
Ronald A. Rensink
, J. Kevin O'Regan
Cambridge Basic Research, Nissan Research & Development, Inc;
Laboratoire de Psychologie Experimentale, CNRS,
Université René Descartes, Paris, France; and
Department of Electrical Engineering, McGill University
When looking at a scene, observers feel that they see its
entire structure in great detail and can immediately notice any
changes in it.
However, when brief blank fields are placed between
alternating displays of an original and a modified scene, a striking
failure of perception is induced:
identification of changes becomes
extremely difficult, even when changes are large and made repeatedly.
Identification is much faster when a verbal cue is provided, showing
that poor visibility is not the cause of this difficulty.
also faster for objects mentioned in brief verbal descriptions of the
These results support the idea that observers never form a
complete, detailed representation of their surroundings.
results also indicate that attention is required to perceive change, and
that in the absence of localized motion signals it is guided on the basis
of high-level interest.
Although people must look in order to see, looking by itself is not
For example, a person who turns his or her eyes toward a bird
singing in a tree will often fail to see it right away, "latching onto" it
only after some effort.
This also holds true for objects in plain view:
a driver whose mind wanders during driving can often miss important
road signs, even when these are highly visible.
In both situations, the
information needed for perception is available to the observer.
Something, however, prevents the observer from using this
information to see the new objects that have entered the field of view.
In this article, we argue that the key factor is attention.
particular, we proposed that the visual perception of change in a scene
occurs only when focused attention is given to the part being changed.
In support of this position, we show that when the low-level cues that
draw attention are swamped, large changes in images of real-world
scenes become extremely difficult to identify, even though these
changes are repeated dozens of times and observers have been told to
Changes are easily identified when a valid verbal cue is
given, indicating that stimulus visibility is not reduced.
also easily identified when made to objects mentioned in brief verbal
descriptions of the scene.
Taken together, these results indicate
that—even when sufficient viewing time has been given—an observer
does not build up a representation of a scene that allows him or her to
perceive change automatically.
Rather, perception of change is
mediated through a narrow attentional bottleneck, with attention