Failures to see: attentive blank stares revealed by change blindness

Change blindness illustrates a remarkable limitation in visual processing by demonstrating that substantial changes in a visual scene can go undetected. Because these changes can ultimately be detected using top-down driven search processes, many theories assign a central role to spatial attention in overcoming change blindness. Surprisingly, it has been reported that change blindness can occur during blink-contingent changes even when observers fixate the changing location [O'Regan, J. K., Deubel, H., Clark, J. J., & Rensink, R. A. (2000). Picture changes during blinks: Looking without seeing and seeing without looking. Visual Cognition, 7, 191-212]. However, eye blinks produce a transient disruption of vision that is independent of any associated changes in the retinal image. We determined whether these 'attentive blank stares' could occur in the absence of blink-mediated visual suppression. Using a flicker change-blindness paradigm we confirm that despite direct attentive fixations, obvious scene changes often remain undetected. We conclude that change detection involves object or feature based attentional mechanisms, which can be 'misdirected' despite the allocation of spatial attention to the position of the change.     

Nothing compares 2 views: change blindness can occur despite preserved access to the changed information

Change blindness, the failure to detect visual changes that occur during a disruption, has increasingly been used to infer the nature of internal representations. If every change were detected, detailed representations of the world would have to be stored and accessible. However, because many changes are not detected, visual representations might not be complete, and access to them might be limited. Using change detection to infer the completeness of visual representations requires an understanding of the reasons for change blindness. This article provides empirical support for one such reason: change blindness resulting from the failure to compare retained representations of both the pre- and postchange information. Even when unaware of changes, observers still retained information about both the pre- and postchange objects on the same trial.     

Evidence for preserved representations in change blindness

People often fail to detect large changes to scenes, provided that the changes occur during a visual disruption. This phenomenon, known as "change blindness," occurs both in the laboratory and in real-world situations in which changes occur unexpectedly. The pervasiveness of the inability to detect changes is consistent with the theoretical notion that we internally represent relatively little information from our visual world from one glance at a scene to the next. However, evidence for change blindness does not necessarily imply the absence of such a representation---people could also miss changes if they fail to compare an existing representation of the pre-change scene to the post-change scene. In three experiments, we show that people often do have a representation of some aspects of the pre-change scene even when they fail to report the change. And, in fact, they appear to "discover" 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.     

Mapping visual attention with change blindness: new directions for a new method

Change blindness provides a new technique for mapping visual attention with unprecedented spatial and temporal resolution. Change blindness can occur when a brief full-field blank interferes with the detection of changes in a scene that occur during the blank. This interference can be overcome by attending to the location of a change. Because changes are detected at attended locations, but not at unattended locations, detection accuracy provides an indirect measure of the distribution of visual attention. The likelihood of detecting a new element in a scene provides a measure of the occurrence of attention at that element’s location. Potential new directions, advantages, and problems with this method are considered.     

Concepts about agency constrain beliefs about visual experience

Recent research exploring phenomena such as change blindness, inattentional blindness, attentional blink and repetition blindness has revealed a number of counterintuitive ways in which apparently salient visual stimuli often go unnoticed. In fact, large majorities of subjects sometimes predict that they would detect visual changes that actually are rarely noticed, suggesting that people have strong beliefs about visual experience that are demonstrably incorrect. However, for other kinds of visual metacognition, such as picture memory, people underpredict performance. This paper describes two experiments demonstrating that both these overpredictions of change detection, and underpredictions of visual memory can be linked with intuitions about the visual experience of different kinds of agents. Subjects predicted more visual change detection and poorer visual memory for mechanical representational systems (e.g. computer programs) when these were anthropomorphized using intentional terminology.     

The development of change blindness: children's attentional priorities whilst viewing naturalistic scenes

Change blindness describes the surprising difficulty of detecting large changes in visual scenes when changes occur during a visual disruption. In order to study the developmental course of this phenomenon, a modified version of the flicker paradigm, based on Rensink, O’Regan & Clark (1997 ), was given to three groups of children aged 6–12 years and to a group of adults. This paradigm tested the ability to detect single colour, presence/absence and location changes of both high and low semantic importance in a complex scene. Semantically important changes were detected more quickly and accurately than less semantically important changes, by all age groups, indicating that children had the same attentional priorities as adults. Older children achieved more efficient and accurate detection of changes than younger children and reached almost adult level at 10–12 years old. These improvements parallel age‐related developments in attention and visual perception.     

内隐觉察的行为和神经活动特征

变化盲视是指在某些条件下人们往往觉察不到视觉场景中实质性的改变。最近研究表明,变化盲视发生时个体虽然不能有意识地报告变化,但却能无意识地对变化刺激进行加工和反应,也就是产生了内隐觉察。内隐觉察能够引导注意、影响反应速度。与觉察和无觉察相比,内隐觉察的眼动模式具有鲜明的特征。与无变化试次相比,盲视试次可以观察到显著的脑电活动变化以及不同的脑区激活。内隐觉察的研究虽然取得了丰富的成果,但也还存在着一些需要明确和解决的问题,如左侧前额叶在内隐觉察中的作用,以及如何将没有视觉干扰的范式应用到变化觉察的神经活动测量中等。     

Change Detection Without Awareness: Do Explicit Reports Underestimate the Representation of Change in the Visual System?

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 redeployment of attention. We discuss these results in relation to theories of scene perception, and propose a reinterpretation of the role of attention in representing change.     

Attentional enhancement opposite a peripheral flash revealed using change blindness

We describe a new method for mapping spatial attentionthat reveals a pooling of attention in the hemifield opposite a peripheralflash. Our method exploits the fact that a brief full-field blank caninterfere with the detection of changes in a scene that occur during theblank. Attending to the location of a change, however, can overcome thischange blindness, so that changes are detected. The likelihood of detecting anew element in a scene therefore provides a measure of the occurrence ofattention at that element's location. Using this measure, we mappedhow attention changes in response to a task-irrelevant peripheral cue. Underconditions of visual fixation, change detection was above chance across theentire visual area tested. In addition, a "hot spot" ofattention (corresponding to near-perfect change detection) elongated alongthe cue-fixation axis, such that performance improved not only at the cuedlocation but also in the opposite hemifield.     

Implicit processing during change blindness revealed with mouse-contingent and gaze-contingent displays

People often miss salient events that occur right in front of them. This phenomenon, known as change blindness, reveals the limits of visual awareness. Here, we investigate the role of implicit processing in change blindness using an approach that allows partial dissociation of covert and overt attention. Traditional gaze-contingent paradigms adapt the display in real time according to current gaze position. We compare such a paradigm with a newly designed mouse-contingent paradigm where the visual display changes according to the real-time location of a user-controlled mouse cursor, effectively allowing comparison of change detection with mainly overt attention (gaze-contingent display; Experiment 2) and untethered overt and covert attention (mouse-contingent display; Experiment 1). We investigate implicit indices of target detection during change blindness in eye movement and behavioral data, and test whether affective devaluation of unnoticed targets may contribute to change blindness. The results show that unnoticed targets are processed implicitly, but that the processing is shallower than if the target is consciously detected. Additionally, the partial untethering of covert attention with the mouse-contingent display changes the pattern of search and leads to faster detection of the changing target. Finally, although it remains possible that the deployment of covert attention is linked to implicit processing, the results fall short of establishing a direct connection.     

On the Failure to Detect Changes in Scenes Across Brief Interruptions

When brief blank fields are placed between alternating displays of an original and a modified scene, a striking failure of perception is induced: The changes become extremely difficult to notice, even when they are large, presented repeatedly, and the observer expects them to occur (Rensink, O'Regan, & Clark, 1997). To determine the mechanisms behind this induced “change blindness”, four experiments examine its dependence on initial preview and on the nature of the interruptions used. Results support the proposal that representations at the early stages of visual processing are inherently volatile, and that focused attention is needed to stabilize them sufficiently to support the perception of change.     

Perceptual conditions necessary to induce change blindness

Change blindness is a failure to detect a change in an scene when the change occurs along with some visual disturbances. Disturbances are thought to play a delocalizing role that affects the saliency of the “target” transient signal coming from the change location, which would otherwise capture attention and render the change visible. For instance, it is hypothesized that the appearance of new objects in the “mudsplashes” paradigm generates transient signals that compete with the target object's transient signal for attracting attention. Thus, experiments using the mudsplashes paradigm do not rule out a possible role of object changes in capturing attention. Here, by reversing image contrast polarity, we develop a new paradigm to produce change blindness when a real global transient signal is the only visual event occurring, with no edges added or deleted except in the target object. The results show that transient signals, per se, are able to prevent change detection. However, abrupt transients are not necessary if object change occurs in the zero-contrast phase of a smoothly fading and reappearing image, leaving attention as the only common factor affecting all cases of change blindness.     

Failure to detect changes to people during a real-world interaction

Recent research on change detection has documented surprising failures to detect visual changes occurring between views of a scene, suggesting the possibility that visual representations contain few details. Although these studies convincingly demonstrate change blindness for objects in still images and motion pictures, they may not adequately assess the capacity to represent objects in the real world. Here we examine and reject the possibility that change blindness in previous studies resulted from passive viewing of 2-D displays. In one experiment, an experimenter initiated a conversation with a pedestrian, and during the interaction, he was surreptitiously replaced by a different experimenter. Only half of the pedestrians detected the change. Furthermore, successful detection depended on social group membership; pedestrians from the same social group as the experimenters detected the change but those from a different social group did not. A second experiment further examined the importance of this effect of social group. Provided that the meaning of the scene is unchanged, changes to attended objects can escape detection even when they occur during a natural, real-world interaction. The discussion provides a set of guidelines and suggestions for future research on change blindness.     

Current Approaches to Change Blindness

Across saccades, blinks, blank screens, movie cuts, and other interruptions, observers fail to detect substantial changes to the visual details of objects and scenes. This inability to spot changes (“change blindness”) is the focus of this special issue of Visual Cognition. This introductory paper briefly reviews recent studies of change blindness, noting the relation of these findings to earlier research and discussing the inferences we can draw from them. Most explanations of change blindness assume that we fail to detect changes because the changed display masks or overwrites the initial display. Here I draw a distinction between intentional and incidental change detection tasks and consider how alternatives to the “overwriting” explanation may provide better explanations for change blindness.     

Reflexive attention attenuates change blindness (but only briefly)

Humans are remarkably insensitive to large changes in a visual display if the change occurs simultaneously with a secondary perceptual event. A widely held view is that this change blindness occurs because the secondary perceptual event prevents the change from capturing attention. However, whereas some studies have shown that top-down attentional priming can attenuate change blindness, the evidence regarding the effect of bottom-up attentional capture on change blindness is less clear-cut. Here, we compare the effects of attentional capture on change detection with participants' performance on a well-established attentional paradigm (a Posner-style cuing task). Experiment 1 established the time course of attentional capture in our paradigm. Experiment 2 demonstrated that this attentional capture was associated with facilitated change detection at short (150-msec), but not long (480-msec), latencies. These data show that reflexive attentional shifts facilitate change detection and are consistent with the view that shifts of attention are a necessary precondition for visual awareness.     

Crossmodal change blindness between vision and touch

Change blindness is the name given to people's inability to detect changes introduced between two consecutively-presented scenes when they are separated by a distractor that masks the transients that are typically associated with change. Change blindness has been reported within vision, audition, and touch, but has never before been investigated when successive patterns are presented to different sensory modalities. In the study reported here, we investigated change detection performance when the two to-be-compared stimulus patterns were presented in the same sensory modality (i.e., both visual or both tactile) and when one stimulus pattern was tactile while the other was presented visually or vice versa. The two to-be-compared patterns were presented consecutively, separated by an empty interval, or else separated by a masked interval. In the latter case, the masked interval could either be tactile or visual. The first experiment investigated visual-tactile and tactile-visual change detection performance. The results showed that in the absence of masking, participants detected changes in position accurately, despite the fact that the two to-be-compared displays were presented in different sensory modalities. Furthermore, when a mask was presented between the two to-be-compared displays, crossmodal change blindness was elicited no matter whether the mask was visual or tactile. The results of two further experiments showed that performance was better overall in the unimodal (visual or tactile) conditions than in the crossmodal conditions. These results suggest that certain of the processes underlying change blindness are multisensory in nature. We discuss these findings in relation to recent claims regarding the crossmodal nature of spatial attention.     

The role of iconic memory in change-detection tasks

In three experiments, subjects attempted to detect the change of a single item in a visually presented array of items. Subjects' ability to detect a change was greatly reduced if a blank interstimulus interval (ISI) was inserted between the original array and an array in which one item had changed ('change blindness'). However, change detection improved when the location of the change was cued during the blank ISI. This suggests that people represent more information of a scene than change blindness might suggest. We test two possible hypotheses why, in the absence of a cue, this representation fails to produce good change detection. The first claims that the intervening events employed to create change blindness result in multiple neural transients which co-occur with the to-be-detected change. Poor detection rates occur because a serial search of all the transient locations is required to detect the change, during which time the representation of the original scene fades. The second claims that the occurrence of the second frame overwrites the representation of the first frame, unless that information is insulated against overwriting by attention. The results support the second hypothesis. We conclude that people may have a fairly rich visual representation of a scene while the scene is present, but fail to detect changes because they lack the ability to simultaneously represent two complete visual representations.     

Changing scenes: memory for naturalistic events following change blindness

Research on scene perception indicates that viewers often fail to detect large changes to scene regions when these changes occur during a visual disruption such as a saccade or a movie cut. In two experiments, we examined whether this relative inability to detect changes would produce systematic biases in event memory. In Experiment 1, participants decided whether two successively presented images were the same or different, followed by a memory task, in which they recalled the content of the viewed scene. In Experiment 2, participants viewed a short video, in which an actor carried out a series of daily activities, and central scenes' attributes were changed during a movie cut. A high degree of change blindness was observed in both experiments, and these effects were related to scene complexity (Experiment 1) and level of retrieval support (Experiment 2). Most important, participants reported the changed, rather than the initial, event attributes following a failure in change detection. These findings suggest that attentional limitations during encoding contribute to biases in episodic memory.     

Changes are not localized before they are explicitly detected

Change detection is in many ways analogous to visual search. Yet, unlike search, successful detection depends not on the salience of features within a scene, but on the difference between the original and modified scene. If, as in search, pre-attentive mechanisms guide attention to the change location, the change itself must produce a preattentively detectable signal. Despite recent evidence for implicit representation of change in the absence of conscious detection, few studies have yet explored whether attention is guided to a change location prior to explicit detection. In four “change blindness” experiments using several variants of the “flicker” task, we tested the hypothesis that implicit or preattentive mechanisms guide change localization prior to explicit detection. None of the experiments revealed improved localization of changes prior to explicit reports of detection, suggesting that implicit detection of change does not contribute to the eventual explicit localization of a change. Instead, change localization is essentially arbitrary, driven by the salience of features within scenes.     

Attenuated Change Blindness for Exogenously Attended Items in a Flicker Paradigm

When two scenes are alternately displayed, separated by a mask, even large, repeated changes between the scenes often go unnoticed for surprisingly long durations. Change blindness of this sort is attenuated at “centres of interest” in the scenes, however, supporting a theory of change blindness in which attention is necessary to perceive such changes (Rensink, O'Regan, & Clark, 1997). Problems with this measure of attentional selection - via verbally described “centres of interest” - are discussed, including worries about describability and explanatory impotence. Other forms of attentional selection, not subject to these problems, are employed in a “flicker” experiment to test the attention-based theory of change detection. Attenuated change blindness is observed at attended items when attentional selection is realized via involuntary exogenous capture of visual attention - to late-onset items and colour singletons - even when these manipulations are uncorrelated with the loci of the changes, and are thus irrelevant to the change detection task. These demonstrations ground the attention-based theory of change blindness in a type of attentional selection which is understood more rigorously than are “centres of interest”. At the same time, these results have important implications concerning the nature of exogenous attentional capture.