When looking at a scene, observers feel that they see its entire structure in great detail and can immediately notice any changes in it. However, when brief blank fields are placed between alternating displays of an original and a modified scene, a striking failure of perception is induced: identification of changes becomes extremely difficult, even when changes are large and made repeatedly. Identification is much faster when a verbal cue is provided, showing that poor visibility is not the cause of (...) this difficulty. Identification is also faster for objects mentioned in brief verbal descriptions of the scene. These results support the idea that observers never form a complete, detailed representation of their surroundings. In addition, results also indicate that attention is required to perceive change, and that in the absence of localized motion signals it is guided on the basis of high-level interest. (shrink)

Five aspects of visual change detection are reviewed. The first concerns the concept of change itself, in particular the ways it differs from the related notions of motion and difference. The second involves the various methodological approaches that have been developed to study change detection; it is shown that under a variety of conditions observers are often unable to see large changes directly in their field of view. Next, it is argued that this “change blindness” indicates that focused attention is (...) needed to detect change, and that this can help map out the nature of visual attention. The fourth aspect concerns how these results affect our understanding of visual perception—for example, the implication that a sparse, dynamic representation underlies much of our visual experience. Finally, a brief discussion is presented concerning the limits to our current understanding of change detection. (shrink)

One of the more powerful impressions created by vision is that of a coherent, richly-detailed world where everything is present simultaneously. Indeed, this impression is so compelling that we tend to ascribe these properties not only to the external world, but to our internal representations as well. But results from several recent experiments argue against this latter ascription. For example, changes in images of real-world scenes often go unnoticed when made during a saccade, flicker, blink, or movie cut. This "change (...) blindness" provides strong evidence against the idea that our brains contain a picture-like representation of the scene that is everywhere detailed and coherent. (shrink)

In this chapter, the impact of “functional blindness” during saccades—rapid point-to-point eye movements—on the current theories of perception is explored. These saccades cause gaps in the visual stream that reaches our mental representation of the environment. A detailed explanation of the phenomenon is provided, from its physical and anatomical causes to its functional effect on perception. Several experiments and studies pertaining to the study are discussed to support the conclusions drawn at the end of the chapter. The chapter posits that (...) this phenomenon supports the assumption that there is an area of the brain responsible for maintaining representations of the visual world, which allows inferences to be made during those visual gaps. These representations are assumed to be based primarily on the general information provided by the stimuli rather than specific details, which allows greater focus on areas of importance to the viewer. (shrink)

Large changes in a scene often become difficult to notice if made during an eye movement, image flicker, movie cut, or other such disturbance. It is argued here that this _change blindness_ can serve as a useful tool to explore various aspects of vision. This argument centers around the proposal that focused attention is needed for the explicit perception of change. Given this, the study of change perception can provide a useful way to determine the nature of visual attention, and (...) to cast new light on the way that it is?and is not?involved in visual perception. To illustrate the power of this approach, this paper surveys its use in exploring three different aspects of vision. The first concerns the general nature of _seeing_. To explain why change blindness can be easily induced in experiments but apparently not in everyday life, it is proposed that perception involves a _virtual representation_, where object representations do not accumulate, but are formed as needed. An architecture containing both attentional and nonattentional streams is proposed as a way to implement this scheme. The second aspect concerns the ability of observers to detect change even when they have no visual experience of it. This _sensing_ is found to take on at least two forms: detection without visual experience (but still with conscious awareness), and detection without any awareness at all. It is proposed that these are both due to the operation of a nonattentional visual stream. The final aspect considered is the nature of visual attention itself?the mechanisms involved when _scrutinizing_ items. Experiments using controlled stimuli show the existence of various limits on visual search for change. It is shown that these limits provide a powerful means to map out the attentional mechanisms involved. (shrink)

Evidence from many different paradigms (e.g. change blindness, inattentional blindness, transsaccadic integration) indicate that observers are often very poor at reporting changes to their visual environment. Such evidence has been used to suggest that the spatio-temporal coherence needed to represent change can only occur in the presence of focused attention. In four experiments we use modified change blindness tasks to demonstrate (a) that sensitivity to change does occur in the absence of awareness, and (b) this sensitivity does not rely on (...) the redeploy- ment of attention. We discuss these results in relation to theories of scene percep- tion, and propose a reinterpretatio n of the role of attention in representing change. (shrink)

We identify two aspects of the problem of maintaining perceptual stability despite an observer's eye movements. The first, visual direction constancy, is the (egocentric) stability of apparent positions of objects in the visual world relative to the perceiver. The second, visual position constancy, is the (exocentric) stability of positions of objects relative to each other. We analyze the constancy of visual direction despite saccadic eye movements.Three information sources have been proposed to enable the visual system to achieve stability: the structure (...) of the visual field, proprioceptive inflow, and a copy of neural efference or outflow to the extraocular muscles. None of these sources by itself provides adequate information to achieve visual direction constancy; present evidence indicates that all three are used.Our final question concerns how information processing operations result in a stable world. The three traditionally suggested means have been elimination, translation, or evaluation. All are rejected. From a review of the physiological and psychological evidence we conclude that no subtraction, compensation, or evaluation need take place. The problem for which these solutions were developed turns out to be a false one. We propose a “calibration” solution: correct spatiotopic positions are calculated anew for each fixation. Inflow, outflow, and retinal sources are used in this calculation: saccadic suppression of displacement bridges the errors between these sources and the actual extent of movement. (shrink)

It has often been assumed that when we use vision to become aware of an object or event in our surroundings, this must be accompanied by a corresponding visual experience (i.e., seeing). The studies reported here show that this assumption is incorrect. When observers view a sequence of displays alternating between an image of a scene and the same image changed in some way, they often feel (or sense) the change even though they have no visual experience of it. The (...) subjective difference between sensing and seeing is mirrored in several behavioral differences, suggesting that these are two distinct modes of conscious visual perception. (shrink)

& Awareness of change within a visual scene only occurs in subjects were aware of, replicated those attentional effects, but the presence of focused attention. When two versions of a.

b>—Several paradigms (e.g. change blindness, inattentional blindness, transsaccadic integra- tion) indicate that observers are often very poor at reporting changes to their visual environment. Such evidence has been used to suggest that the spatio-temporal coherence needed to represent change can only occur in the presence of focused attention. However, those studies almost always rely on explicit reports. It remains a possibility that the visual system can implicitly detect change, but that in the absence of focused attention, the change does not (...) reach awareness and consequently is not reported. To test this possibility, we used a simple change detection paradigm coupled with a speeded orien- tation discrimination task. Even when observers reported being unaware of a change in an item’s orientation, its nal orientation effectively biased their response in the orientation discrimination task. Both in aware and unaware trials, errors were most frequent when the changed item and the probe had incongruent orientations. These results demonstrate that the _nature _of the change can be represented in the absence of awareness. (shrink)

Research over the past half century has produced extensive evidence that observers cannot report or retain all of the details of their visual world from one moment to the next. During the past decade, a new set of studies has illustrated just how pervasive these limits are. For example, early evidence for the failure to detect changes to simple dot patterns (Phillips, 1974) and arrays of letters (Pashler, 1988) generalizes to more naturalistic displays such as photographs and motion pictures (e.g., (...) Levin & Simons, 1997; Rensink, O’Regan, & Clark, 1997; see Rensink, 2002 for a recent review). This failure to report changes (change blindness) can be induced in both simple and naturalistic displays, whenever the change co-occurs with a visual disruption such as an eye movement (Currie, McConkie, Carlson-Radvansky, & Irwin, 1995; Hollingworth, Schrock, & Henderson, 2001), image shift (Blackmore, Brelstaff, Nelson, & Troscianko, 1995), flashed blank screen (Rensink et al., 1997), blink (O’Regan, Deubel, Clark, & Rensink, 2000), transient (O’Regan, Rensink, & Clark, 1999; Rensink, O’Regan, & Clark, 2000), movie cut or pan (Levin & Simons, 1997; Simons, 1996), or an occlusion event (Levin, Simons, Angelone, & Chabris, 2002; Simons & Levin, 1998). Change blindness can also occur in the absence of a disruption, provided the change occurs gradually enough that it does not attract attention (Simons, Franconeri, & Reimer, 2000). -/- Failures of visual awareness have been induced in a number of ways. For example, observers often fail to report a visible but unexpected stimulus when attention is focused on some other object or event in the display (inattentional blindness). As for change blindness, inattentional blindness occurs for both simple (Mack & Rock, 1998; Most et al., 2001) and naturalistic stimuli (Simons & Chabris, 1999). Similarly, repeated instances of an item often go undetected when embedded in a rapid sequence (repetition blindness), a phenomenon that occurs for both words and pictures (Kanwisher, 1987; Kanwisher & Potter, 1990). Observers can also fail to detect a stimulus in a rapid stream of stimuli provided they had to perform an attention-demanding task shortly before the stimulus appeared (Shapiro, Arnell, & Raymond, 1997). The surprisingly large variety of conditions that induce failures of conscious perception reinforces the broad conclusion that we are often unaware of what would otherwise be fully-visible stimuli. -/- Along with an increased appreciation of the limitations of visual awareness has come a renewed interest in using these limitations to explore the nature of the representations and processes underlying our visual experience. Are these limitations due to failures of perception? Of attention? Of memory? What is preserved with and without awareness? -/- The papers in this special issue of the Journal of Vision provide examples of exciting new work on induced failures of visual awareness and the mechanisms that underlie them. For example, several papers examine whether observers are drawn to parts of a display by the stimulus features or whether top-down control or semantic comprehension influence search through a display. Others investigate the nature of and limits on the information that is preserved from one view to the next and how much information needs to be retained for effective perception and action. As guest editors, we hope that this special issue will illustrate how studying the relationship between visual awareness and visual representations can lead to important new insights into the nature of seeing. (shrink)