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An Overview of Inattentional
Blindness
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Mack & Rock (1998) explored the nature of perception when attention
is directed away from a target object. In their task, observers judged
which line of a briefly flashed "+" was longer, the horizontal or
the vertical. On the fourth trial of this task, an unexpected object
was preseted at the same time as the plus at a different position
on the screen. When the plus was presented at fixation and the unexpected
object was presented parafoveally, 25% of observers did not see the
unexpected object. Even more startling, when the plus was presented
parafoveally and the unexpected object was presented at fixation,
nearly 75% of observers failed to detect the object. Perhaps more
strikingly, when the unexpected object was meaningful (e.g., a smily
face or the subject's name), detection was substantially more likely.
Mack and Rock conclude that without attention, nothing is consciously
perceived.
These recent studies are consistent
with an earlier line of work examining the detection of unexpected
events during a divided attention tasks (e.g., Neisser, 1979). In
these studies, observers monitored one event while simultaneosly ignoring
another similar event. For example, observers monitored one team of
players passing a basketball while ignoring another team also passing
a ball. Typically in these tasks the displays were physically superimposed
so that the players were overlapping and partially transparent. While
observers this task (e.g., counting the passes of the attended team),
an unexpected event (UE) occurred. For example, a woman carrying an
open umbrella might across the court (the UE was also partially transparent).
As in Mack & Rock's studies, observers often failed to see the
UE. These studies demonstrate that attention is directed to objects
and events rather than spatial locations -- the attended event was
literally superimposed on the unattended event, yet observers still
did not see the UE. Furthermore, these studies showed that observers
could miss a suprathreshold UE that lasted for several seconds (as
opposed to 200ms in Mack & Rock's studies). |
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