Attention : Change Blin Dness and Inatt Entional Blindnes S R a Rensink, University of British Columbia, Vancouver, BC, Canada à 2009 Elsevier Inc
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a0005 Attention : Change Blin dness and Inatt entional Blindnes s R A Rensink, University of British Columbia, Vancouver, BC, Canada ã 2009 Elsevier Inc. All rights reserved. Glossary is false – there are severe limits to what we can consciously experience in everyday life. Much of g0005 Change blindness – The failure to visually the evidence for this claim has come from two experience changes that are easily seen once phenomena: change blindness (CB) and inatten- noticed. This failure therefore cannot be due tional blindness (IB). to physical factors such as poor visibility; CB refers to the failure of an observer to visu- perceptual factors must be responsible. ally experience changes that are easily seen once Focused attention is believed to be necessary noticed. This can happen even if the changes are to see change, with change blindness large, constantly repeat, and the observer has been resulting if such attention is not allocated to informed that they will occur. A related phenome- the object at the moment it changes. non is IB – the failure to visually experience an g0010 Diffuse attention – A type of attention that is object or event when attention is directed else- spread out over large areas of space. It is where. For example, observers may fail to notice believed to be space-based rather than an unexpected object that enters their visual field, object-based. even if this object is large, appears for several g0015 Focused attention – A type of attention seconds, and has important consequences for the restricted to small spatial extents. It is selection of action. believed to act on small areas of space or on Both phenomena involve a striking failure to relatively small objects. report an object or event that is easily seen once g0020 Implicit perception – Perception that takes noticed. As such, both are highly counterintuitive, place in the absence of conscious awareness not only in the subjective sense that observers have of the stimulus. It is generally believed to take difficulty believing they could fail so badly at place in the absence of any type of attention. seeing but also in the objective sense that these g0025 Inattentional blindness – The failure to findings challenge many existing ideas about how visually experience the appearance of an we see. But as counterintuitive as these phenom- object or event that is easily seen once ena are, progress has been made in understanding noticed. Attention (likely, diffuse attention) is them. Indeed, doing so has allowed us to better thought to be necessary for such an understand the limitations of human perception in experience. Inattentional blindness typically everyday life and to gain new insights into how our occurs when attention is diverted, such as visual systems create the picture of the world that when the observer engages in an we experience each moment our eyes are open. attentionally demanding task elsewhere, and does not expect the appearance of the object or event. Change Blindness Background The ability to see change is extremely useful in s00 05 Introductio n coping with everyday life: we can monitor the movement of nearby automobiles (as drivers or p0005 As obser ver s, we generally have a strong impres- pedestrians), notice sudden changes in the posture sion of seeing everything in front of us at any or location of people in front of us, and notice that moment. But compelling as it is, this impression the sky is quickly darkening. Given the importance 1 2 Attention: Change Blindness and Inattentional Blindness of perceiving change and the fact that most observers were found to be surprisingly poor at humans can survive reasonably well in the world, detecting changes made under such conditions. it follows that our ability to perceive change must The next wave of studies, begun in the 1970s, was be such that few events in the world escape our based on a more systematic examination of these notice. This agrees nicely with our impression that effects. This work uncovered a general limit to the we perceive at each moment most, if not all, ability to detect gap-contingent changes under a objects and events in front of us. wide variety of conditions; this eventually formed p0025 Failures to see change have long been noticed, the basis for the proposal of a limited-capacity visual but they were usually taken to be temporary aber- short-term memory (vSTM). Likewise, a general rations, with nothing useful to say about vision. lack of ability was found for detection of saccade- This attitude began to change in the early twenti- contingent changes, which was traced to a limited eth century, when film editors discovered an inter- transsaccadic memory. Both lines of research esting effect: when the audience moved their eyes were eventually linked by the proposal that trans- across the entire screen (e.g., when the hero exited saccadic memory and vSTM were in fact the same on the left side and the femme fatale entered on system. the right) almost any change made during this time A third wave began in the mid-1990s, extending (e.g., a blatant change of costume) would often go the methodology and results of earlier work in unnoticed. A similar blindness to change could be several ways. To begin with, stimuli were often induced by making it during a loud, sudden noise more complex and realistic: images of real-world (e.g., a gunshot), during which the audience would scenes or dynamic events were used in place of momentarily close their eyes. simple figures. Next, changes were often repeated p0030 The scientific study of this ef f ect began in the rather than occurring just once, allowing the use of mid-1950s, with work on position changes in dot time as well as accuracy to measure performance arrays and other simple stimuli. Here, a change in (Figure 1). Third, blindness was induced via sev- one of the items was typically made contingent on a eral new kinds of manipulation, such as making temporal gap that lasted several seconds. A separate changes during a film cut or during the appearance line of studies was also begun that investigated of sudden splats elsewhere in the image. Finally, all the perception of displacements made contingent these effects – as well as the earlier ones – were on an eye movement (or saccade). In all cases, accounted for by the proposal that attention is One-shot paradigm Flicker paradigm(a)(b) f0005 Figure 1 Example of a technique to induce CB. Here the change is made during a brief gap between the original and the modified stimulus. (a) One-shot paradigm. A single alternation of the stimuli is used, and the observer must respond to it. Performance is measured by accuracy of detection (or identification or localization). (b) Flicker Au2 paradigm. Stimuli are continually cycled under the observer responds. Performance is measured by the time taken until the change is detected (or identified or localized). Both types of measurement paradigm can also be applied to other techniques, such as changes made during saccades or splats. Attention: Change Blindness and Inattentional Blindness 3 necessary to see change. This work therefore visual event. For example, when a person is seen showed that this CB is a general and robust phe- walking, their legs are seen at various positions nomenon that can last for several seconds, and can over time. This kind of perception suggests – be connected to known perceptual mechanisms. As although does not prove – that the underlying such, it supported the idea that change perception representation has a spatiotemporal continuity of is an important part of perception, and that study- some kind. In contrast, difference is based on an ing its failure can cast light on mechanisms central atemporal comparison of structures that may or to our experience of the world. may not exist simultaneously, for example, com- paring the height of two people. This kind of s00 20 Conceptual Distinctions perception allows for the possible involvement of long-term memory elements that are only inter- p0045 A c lear under standing of CB – and its inver se, mittently engaged. change perception – has been slow to emerge. This distinction is important. Change detection This is partly due to the nature of change itself. and difference detection can be distinguished, at Although this concept appears simple, attempts to least conceptually; it is important to consider the formalize it over the years – from the earliest type of experiment used when discussing either one. Greek thinkers to modern philosophers – have Spotting the difference between two side-by-side generally encountered difficulties. However, a stimuli may not engage the same perceptual number of important distinctions have become mechanisms as detecting a change in successively clear, which have helped our understanding of CB. presented stimuli. Failure to make this distinction can lead to erroneous conclusions being drawn s00 25 Change versus motion about the mechanisms involved. p0050 The human perce ption of temporal variation is handled by two separate systems: a motion- detection system for variation in regards to a partic- Experimental Approaches and Results ular location and a change-detection system for variation in regards to structure. Temporal varia- All studies to date have been based on much the tions in the world activate both systems to some same design: an initial stimulus is first presented extent. For example, a moving automobile will acti- (e.g., a picture), an altered version is then shown vate motion detectors over the relevant part of the (e.g., some object in it is removed), and the ability visual field, although these will not be able to deter- of the observer to perceive the change is then mine whether there is an enduring spatiotemporal measured (see Figure 1).