These effects suggest that
attention was implicitly, but not explicitly, captured by the unexpected object.
Although subjects could not report the configuration of the dots and in fact
never noticed that they were grouped to form the illusion, their judgments were
still influenced by the dot configuration. Further studies are needed to explore
implicit attentional capture in the absence of explicit attentional capture,
especially in the context of selective-looking paradigms. Although the findings
of IB suggest that novel, distinctive objects do not necessarily explicitly
capture attention, perhaps attentional capture failed in these experiments
because the objects were static and presented too briefly (Simon, 2000). During
the 1970s and 1980s, the 'selective looking' paradigm was developed as a visual
analog of dichotic listening to explore the detection of sustained, dynamic,
unexpected visual events (Becklen & Cervone, 1983) . A dramatic example of
inattentional blindness (IB) comes from a selective-looking study that used a
display with two superimposed teams, each playing a ball game. When observers
monitor one of the two overlapping teams and not the other (e.g. the three
players wearing white shirts and not the three players wearing black shirts),
they often failed to see a woman with an open umbrella appear from one side of
the screen and walk across the display (Becklen & Cervone, 1983). The appearance
of this new, salient object did not capture attention. Chabris & Simons (1999)
set out to replicate and extend these studies and to revive the
selective-looking paradigm as a tool for the study of attentional capture. As in
the basketball-game studies, subjects counted the passes made by either the
white team or the black team. The two teams and the unexpected event were filmed
separately and then superimposed into a single video display to replicate the
original displays. After about 45 seconds of the display, while the subjects
were performing the counting task, a woman carrying an open umbrella walked
across the display and exited the other side five seconds later. As in the
earlier study, many subjects did not notice the umbrella woman. Another set of
conditions was used with a person wearing a gorilla suit. Again, Chabris &
Simons (1999) found a great deal of IB. Although these studies suggest that
salient new objects in complex displays do not explicitly capture attention, the
degree of inattentional blindness could have been due to some oddity of the
displays. Partially transparent displays are not typical of our real-world
visual experience, so they may have impaired subjects' ability to detect the
unexpected object.
Chabris & Simon (1999) thus further tested subjects with a
set of displays in which all of the players and the unexpected object were
opaque and could occlude each other. If IB in the earlier studies and in this
replication were due to some oddity caused by the transparent displays, then
subjects should easily detect the umbrella woman and gorilla in these opaque
conditions. However, they did not, as approximately 35% of subjects did not see
the fully visible umbrella woman and gorilla. In one extra condition, the opaque
gorilla stopped halfway across the display, turned to face the camera, thumped
its chest, and then exited on the other side of the screen. Even in this
condition, half of the observers did not see it. In the static IB paradigm,
observers often fail to notice the onset of a new, unexpected object in the
display. This finding is somewhat consistent with findings from the Irrelevant
Feature Search paradigm showing that when attention is focused on some other
part of a display, an abrupt onset might not implicitly capture attention
(Simon, 2000) . Implicit attentional capture in the Irrelevant Feature Search
paradigm requires that attention must not be focused elsewhere. The static IB
results are consistent with this notion and suggest that when attention is
engaged elsewhere, new objects can fail to explicitly capture attention as well.
However, the selective-looking results raise some problems for this explanation
for the failure of attentional capture. In the selective-looking paradigm,
observers are focusing on multiple objects and the unexpected object literally
passes through the attended locations. Attention is distributed across the
display, but focused on other objects and events (Haines, 1991). Thus, failed
attentional capture cannot be attributed to spatially focused attention (Yantis
& Jonides, 1990). However, the more general notion of attentional engagement may
help to explain both types of failed attentional capture. In both implicit and
explicit paradigms, when attention is engaged, the likelihood of capture is
reduced. In the static IB case and in the implicit search tasks, attention is
often focused on a clearly defined spatial region and in selective-looking
tasks, attention is engaged by objects and events. Do these two types of
attentional engagement, location-based and object/event-based, have equivalent
effects on capture? (Simons, 2000) In most real-world settings, observers are
actively engaged in some task or goal, and the degree of attentional engagement
can vary substantially. For example, driving a car in traffic in a Canadian
snowstorm will probably limit the focus of attention to a relatively small
region, perhaps increasing the degree of engagement relative to driving under
normal conditions. The degree of engagement may well influence the probability
of both implicit and explicit attentional capture. Yet, no studies have looked
at the effects of varying the level of attentional engagement on capture
(Simons, 2000).
