We studied the role of attention and task demands for implicit change detection. Subjects engaged in an object sorting task performed in a virtual reality environment, where we changed the properties of an object while the subject was manipulating it. The task assures that subjects are looking at the changed object immediately before and after the change. Our results demonstrate that in this situation subjects ' ability to notice changes to the object strongly depends on momentary task demands. Surprisingly, frequent noticing is not guaranteed by task relevance of the changed object attribute per se, but the changed object attribute needs to be task relevant at exactly the right times. Also, the simplicity of the used objects indicates that change blindness occurs in situations where the visual short term memory load is minimal, suggesting a potential dissociation between short term memory limitations and change blindness. Finally, we found that changes may even go unnoticed if subjects are visually tracking the object at the moment of change. Our experiments suggest a highly purposive and task specific nature of human vision, where information extracted from the fixation point is used for certain computations only “just in time ” when needed to solve the current goal.

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In this paper I explore a brand of scepticism about perceptual experience that takes its start from recent work in psychology and philosophy of mind on change blindness and related phenomena. I argue that the new scepticism rests on a problematic phenomenology of perceptual experience. I then consider a strengthened version of the sceptical challenge that seems to be immune to this criticism. This strengthened sceptical challenge formulates what I call the problem of perceptual presence. I show how this problem can be addressed by drawing on an enactive or sensorimotor approach to perceptual consciousness. Our experience of environmental detail consists in our access to that detail thanks to our possession of practical knowledge of the way in which what we do and sensory stimulation depend on each other. Traditional scepticism about perceptual experience questions whether we can know that things are as we experience them as being. This paper targets a new form of scepticism about experience that takes its start from recent work in perceptual psychology and philosophy of mind. The new scepticism questions whether we even have the perceptual experience we think we have. According to the new scepticism, we have radically false beliefs about what our perceptual experience is like. Perceptual consciousness is a kind of false consciousness; a sort of confabulation. The visual world is a grand illusion. The new scepticism raises important questions for philosophy, psychology, and consciousness studies. What is the character of our perceptual experience? And who does the sceptic mean by ‘we ’ anyway? Ordinary perceivers? Ordinary perceivers in unusual reflective contexts? Or psychologists and philosophers? These are surprisingly difficult questions. I argue, in what follows, that the new scepticism, and perhaps also the new perceptual psychology it has spawned, rests on a misguided and overly simplistic account of perceptual phenomenology.

this memory and can explicitly report details of a changed object in response to probing questions. The results of these real-world change detection studies are discussed in the context of broader claims about change blindness. 2002 Elsevier Science (USA) Our experience of a rich, stable visual world often leads to the intuitive belief that our representations of that world are correspondingly detailed and precise. But increasing evidence for "change blindness," the inability to detect large changes to scenes from one glance to the next, has inspired claims that little to no information about the world is preserved in visual short term memory (e.g., O'Regan, 1992; Rensink, 2000a, 2000b). Such claims have some historical precedents (e.g., Gibson, 1986/1979; Hochberg, 1986; Stroud, 1955), but they do not necessarily follow from change blindness. Change blindness could occur for many reasons, even when observers have representations of the pre-change scene (Simons, 2000b). For example, change blindness could reflect a failure to compare representations of the pre- and post-change scene. Here, we present evidence that supports this possibility by showing that some subjects who fail to report a change can subsequently report features of the pre-change object when asked

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We are interested in saccade contingent scene updates where the visual information presented in a display is altered while a saccadic eye movement of an unconstrained, freely moving observer is in progress. Since saccades typically last only several tens of milliseconds depending on their size, this poses difficult constraints on the latency of detection. We have integrated two complementary eye trackers in a virtual reality helmet to simultaneously 1) detect saccade onsets with very low latency and 2) track the gaze with high precision albeit higher latency. In a series of experiments we demonstrate the system's capability of detecting saccade onsets with sufficiently low latency to make scene changes while a saccade is still progressing. While the method was developed to facilitate studies of human visual perception and attention, it may find interesting applications in human-computer interaction and computer graphics.

Eye movements were monitored while participants performed a change detection task with images of natural scenes. An initial and a modified scene image were displayed in alternation, separated by a blank interval (flicker paradigm). In the modified image, a single target object was changed either by deleting that object from the scene or by rotating that object 90º in depth. In Experiment 1, fixation position at detection was more likely to be in the target object region than in any other region of the scene. In Experiment 2, participants detected scene changes more accurately, with fewer false alarms, and more quickly when allowed to move their eyes in the scene than when required to maintain central fixation. These data suggest a major role for fixation position in the detection of changes to natural scenes across discrete views. When we view natural scenes, our impression is that the mind constructs something like an internal photographic image of the entire field of view. However, investigations of visual short-term memory (VSTM) across saccadic eye movements suggest that the visual information retained from one eye fixation to the next is abstracted away from low-level sensory stimulation and that VSTM preserves information from only a small portion of the visual

Our knowledge of the way that the visual system operates in everyday behavior has, until recently, been very limited. This information is critical not only for understanding visual function, but also for understanding the consequences of various kinds of visual impairment, and for the development of interfaces between human and artificial systems. The development of eye trackers that can be mounted on the head now allows monitoring of gaze without restricting the observer's movements. Observations of natural behavior have demonstrated the highly task-specific and directed nature of fixation patterns, and reveal considerable regularity between observers. Eye, head, and hand coordination also reveals much greater flexibility and task-specificity than previously supposed. Experimental examination of the issues raised by observations of natural behavior requires the development of complex virtual environments that can be manipulated by the experimenter at critical points during task performance. Experiments where we monitored gaze in a simulated driving environment demonstrate that visibility of task relevant information depends critically on active search initiated by the observer according to an internally generated schedule, and this schedule depends on learnt regularities in the environment. In another virtual environment where observers copied toy models we showed that regularities in the spatial structure are used by observers to control eye movement targeting. Other experiments in a virtual environment with haptic feedback show that even simple visual properties like size are not continuously available or processed automatically by the visual system, but are dynamically acquired and discarded according to the momentary task demands.

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 �irtual 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. © 2000

In the not-too-distant past, vision was often said to involve three levels of processing: a low level concerned with descriptions of the geometric and photometric properties of the image, a high level concerned with abstract knowledge of the physical and semantic properties of the world, and a middle level concerned with anything not handled by the other two. 1 The negative definition of mid-level vision contained in this description reflected a rather large gap in our understanding of visual processing: How could the here-and-now descriptions of the low levels combine with the enduring knowledge of the high levels to produce our perception of the surrounding world? A number of experimental and theoretical efforts have been made over the past few decades to solve this "mid-level crisis". One of the more recent of these is based on the phenomenon of change blindness—the difficulty in seeing a large change in a scene when the transients accompanying that change no longer convey information about its location (Rensink, O'Regan, & Clark, 1997; Rensink, 2000a). Phenomenologically, this effect is quite striking: the change typically is not seen for several seconds, after which it suddenly snaps into awareness. 2 During the time the change remains "invisible", there is an apparent