Do we automatically really
become aware of salient events in our visual environment, particularly events
that have behavioral consequences? Are we automatically become aware of a
salient new object if it unexpectedly appeared in front of us? And, if so, would attentional capture allow us not only to modify our behavior implicitly in order
to accomplish an existing goal but also to select a new behavioral goal? These
are questions which need to be addressed in future research. Perhaps we may have
had an auto-mobile accident and the other driver claimed he did not see us even
though you were right in front of him. Although we might intuitively believe
that unusual, unexpected and salient objects will capture attention, leading to
awareness, they often do not. In this example, driving performance might have
been affected if our car implicitly captured attention, but that does not really
tell us why he did not see us and it probably could not have prevented a
collision. In most real-world settings, the critical question of interest is not
whether an object will implicitly affect performance, but whether it will
explicitly capture attention and reach awareness, thereby allowing us to modify
our behavior and select new goals (Simon, 2000). Although much, if not most, of
perception and performance occurs without awareness, we feel that when salient
events occur, we should become aware of them so that we can intentionally change
our behavior. The implicit attention capture paradigms explore how well
observers can ignore something they expect but know to be irrelevant, whereas in
explicit attentional capture, the critical question is how likely subjects are
to notice something that is potentially relevant, but that they do not expect.
Recent studies of explicit attentional capture reveal a surprising degree of
blindness to salient or unusual events that we might expect to cap-ture
attention. For example, observers often fail to notice surprisingly large, but
unexpected changes to their visual world, such as a change to the identity of
the central actor in a brief movie (Levin & Simons, 1997). Most subjects
intuitively believe that such changes should capture attention and be detected,
both because of their magnitude and their potential behavioral relevance (Levin
et al., 2000). More relevant for the focus on the driving situation, is the fact
that people sometimes fail to notice an unexpected object or event altogether.
This phenomenon is now commonly known as inattentional blindness (IB) (Mack &
Rock, 1998) .
Studies of inattentional blindness are among the few direct
explorations of explicit attentional capture by complex visual events. Newby &
Rock (1998) used a static inattentional blindness paradigm for studying explicit
attentional capture. In their task, subjects decided which arm of a briefly
presented cross was longer. After several such trials, subjects viewed a
critical trial during which another object unexpectedly appeared along with the
cross. Afterwards, subjects were asked whether they had noticed anything that
had not been present on the previous trials. When the cross appeared at fixation
and the unexpected object appeared away from fixation, approximately 25% of
subjects were inattentionally blind. This mean the unexpected object did not
explicitly capture attention and they did not notice it. Interestingly though,
when the cross appeared away from fixation and the unexpected object appeared at
fixation, nearly 75% were inattentionally blind 28 . Even when the object was a
different color or moved stroboscopically, observers were often inattentionally
blind 28 . These findings show that a salient new object does not always
explicitly capture attention. Simon (2000) points out that even in the absence
of explicit attentional capture, the object may still implicitly affect
performance. Although most studies of explicit attentional capture focus on
whether or not observers notice an unexpected object, even in the absence of
awareness the object might still influence performance. An object might
implicitly capture attention even when it fails to do so explicitly. Several
studies using the static inattentional blindness paradigm have explored this
question by examining whether observers show priming for the unexpected object
that they did not notice. For example, observers are more likely to complete
word fragments with a word that had appeared in the display even if they had not
reported seeing it (Mack & Rock, 1998). Furthermore, even unattended background
information can influence performance. Moore and Egeth (1997) used a variant of
the static IB paradigm in which the cross was replaced by two horizontal lines
and subjects were asked to judge which was longer. Random dots appeared in the
background of the display on each of the initial trials. On the critical trial,
the dots were arranged to produce either the Ponzo or the Müller-Lyer illusion.
Although subjects rarely noticed the pattern in the dots, their judgments of
line length were clearly influenced by the illusions.
