How likely are subjects to notice something salient and potentially relevant that they do not expect? Recently, several new paradigms exploring this question have found that, quite often, unexpected objects fail to capture attention. This, phenomenon known as ‘inattentional blindness’ has been brought forth by Simon (2000) who raised the intriguing possibility that salient stimuli, including the appearance of new objects, might not always capture attention in the real world. For example, a driver may fail to notice another car when trying to turn. With regards to this, in the context of driver attention, this (draft) proposal predicts that intattentional blindness may be the cause of the majority of automobile accidents, and that attentional capture may be improved by expanding the attentional set of the driver through training in virtual driving settings.
This review first considers evidence for the effects of irrelevant features both on performance, by implicit attentional capture and on awareness, by explicit attentional capture. Together studies of implicit attentional capture and recent studies of inattentional blindness can provide a fuller understanding of the varieties of attentional capture, and has important implications for real world driving situations. Two general definitions have been used in the study of attentional capture. Explicit attentional capture occurs when a salient and unattended stimulus draws attention, leading to awareness of its presence. Implicit attentional capture is revealed when a salient and irrelevant stimulus affects performance on another task, regardless of whether or not subjects are aware of the stimulus (Simon, 2000). Explicit attentional capture for examp...
le, occurs when someone across a room says our name or waves vigorously, and that stimulus signal sets itself apart from the background and we become aware of its source (Simon, 2000). Typically, studies determine whether capture has occurred by asking subjects whether they noticed the critical stimulus. Several recent studies of explicit attentional capture have found that when observers are focused on some other object or event, they often fail to notice salient and distinctive objects, a phenomenon that is termed inattentional blindness (IB). Although the use of explicit reports was one of the first approaches used to study attentional capture , most studies have focused on implicit attentional capture. These studies make the critical stimulus irrelevant to the primary task and infer capture of attention based on different patterns of response times or eye movements. (Simon, 2000).
Four distinct paradigms have been used to explore implicit attentional capture by measuring the effects of an irrelevant stimulus on performance of a primary task visual search task. These have already been commonly discussed directly or indirectly before by researchers (eg. In PSY 375 lectures) so they will be briefly presented in a tabular form (See Appendix 1).
The primary debate in the literature on implicit attentional capture focuses on which features might automatically draw attention regardless of the expectations and attentional set of the observer. Evidence from the Pre-cueing paradigm suggests that attentional capture does not occur in the absence of the appropriate attentional set. Findings from each of the other paradigms suggest that stimulus-driven capture can occur, particularly by the abrupt onset of a new object. All of thes
studies explore the degree to which subjects can ignore something they know to be irrelevant. During performance of these tasks, observers often do not even notice the irrelevant feature despite its effects on their search performance (Yantis, 1993). In fact, even distinctive features that are presented below a subjective threshold for awareness can implicitly capture attention and affect performance (McCormick, 1997) . Evidence for implicit attentional capture is critical to understanding the mechanisms underlying visual search and for determining whether a perceptual event can automatically influence performance. Furthermore, such implicit effects can have a dramatic influence on our execution of real-world tasks and goals. For example, much of our driving performance probably reflects implicit detection of salient events (such as cars turning or slowing down) leading to corresponding adjustments to our behavior. A good proportion of perception occurs without awareness, and we need to be able to adjust our behavior without necessarily becoming aware of the cause or even the need for adjustment (Simon, 2000). 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
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