Iconic memory for natural scenes: Evidence using a modified change-detection procedure

ABSTRACT

Change blindness for the contents of natural scenes suggests that only items that are attended while the scene is still visible are stored, leading some to characterize our visual experiences as sparse. Experiments on iconic memory for arrays of discrete symbols or objects, however, indicate observers have access to more visual information for at least several hundred milliseconds at offset of a display. In the experiment presented here, we demonstrate an iconic memory for complex natural or real-world scenes. Using a modified change detection task in which to-be changed objects are cued at offset of the scene, we show that more information from a natural scene is briefly stored than change blindness predicts and more than is contained in visual short-term memory. In our experiment, a cue appearing 0, 300, or 1000?msec after offset of the pre-change scene or at onset of the second scene presentation (a Post Cue) directed attention to the location of a possible change. Compared to a no-cue condition, subjects were significantly better at detecting changes and identifying what changed in the cue condition, with the cue having a diminishing effect as a function of time and no effect when its onset coincided with that of the second scene presentation. The results suggest that an iconic memory of a natural scene exists for at least 1000?msec after scene offset, from which subjects can access the identity of items in the pre-change scene. This implies that change blindness underestimates the amount of information available to the visual system from a brief glance of a natural scene.     

What's new in visual masking?

A brief display that is clearly visible when shown alone can be rendered invisible by the subsequent presentation of a second visual stimulus. Several recently described backward masking effects are not predicted by current theories of visual masking, including masking by four small dots that surround (but do not touch) a target object and masking by a surrounding object that remains on display after the target object has been turned off. A crucial factor in both of these effects is attention: almost no masking occurs if attention can be rapidly focused on the target, whereas powerful masking ensues if attention directed at the target is delayed. A new theory of visual masking, inspired by developments in neuroscience, can account for these effects, as well as more traditional masking effects. In addition, the new theory sheds light on related research, such as the attentional blink, inattentional blindness and change blindness.     

情绪诱发的视盲：一种独特的功能性视盲

功能性视盲是指由于某种原因导致正常的视觉系统出现视觉觉察丧失的现象, 例如变化知盲、注意瞬脱等都属于功能性视盲。情绪诱发的视盲指的是一个与任务无关的情绪性刺激的呈现吸引了注意以致个体无法对快速呈现的靶刺激有所觉察的现象。与注意瞬脱特别是情绪性注意瞬脱相比, 情绪诱发的视盲是以情绪刺激为干扰刺激, 考察情绪刺激如何以自下而上的方式吸引注意并干扰靶刺激的加工, 因此有着自己的特点：它没有lag1节省现象, 也没有像注意瞬脱那样严格的时间窗口限制, 不受干扰刺激与靶刺激物理特征相似程度的限制, 在心理机制上属于早期知觉阶段的加工竞争等等。情绪诱发的视盲表明情绪对注意在时间和空间两个维度上都有吸引或干扰作用。未来可以从考察神经机制、了解影响因素等多方面深化此领域的研究。     

类别意义连结在无意视盲中的作用

本研究考察在无注意定势的参与下,类别信息的意义连结对于无意视盲的作用。被试在实验任务之前观察、学习某一类别的若干刺激,以激活其类别概念和表征。结果表明,启动相关类别概念的被试在非注意情况下觉察到非预期的、显著刺激的可能性更大。这说明,意义连结可以广泛地作用于类别刺激,即使没有注意定势的影响,也能自动地注意到相关的刺激,从而促进其意识的加工。     

What you see is what you set: sustained inattentional blindness and the capture of awareness

This article reports a theoretical and experimental attempt to relate and contrast 2 traditionally separate research programs: inattentional blindness and attention capture. Inattentional blindness refers to failures to notice unexpected objects and events when attention is otherwise engaged. Attention capture research has traditionally used implicit indices (e.g., response times) to investigate automatic shifts of attention. Because attention capture usually measures performance whereas inattentional blindness measures awareness, the 2 fields have existed side by side with no shared theoretical framework. Here, the authors propose a theoretical unification, adapting several important effects from the attention capture literature to the context of sustained inattentional blindness. Although some stimulus properties can influence noticing of unexpected objects, the most influential factor affecting noticing is a person's own attentional goals. The authors conclude that many--but not all--aspects of attention capture apply to inattentional blindness but that these 2 classes of phenomena remain importantly distinct.     

The ventriloquist effect does not depend on the direction of deliberate visual attention

It is well known that discrepancies in the location of synchronized auditory and visual events can lead to mislocalizations of the auditory source, so-called ventriloquism. In two experiments, we tested whether such cross-modal influences on auditory localization depend on deliberate visual attention to the biasing visual event. In Experiment 1, subjects pointed to the apparent source of sounds in the presence or absence of a synchronous peripheral flash. They also monitored for target visual events, either at the location of the peripheral flash or in a central location. Auditory localization was attracted toward the synchronous peripheral flash, but this was unaffected by where deliberate visual attention was directed in the monitoring task. In Experiment 2, bilateral flashes were presented in synchrony with each sound, to provide competing visual attractors. When these visual events were equally salient on the two sides, auditory localization was unaffected by which side subjects monitored for visual targets. When one flash was larger than the other, auditory localization was slightly but reliably attracted toward it, but again regardless of where visual monitoring was required. We conclude that ventriloquism largely reflects automatic sensory interactions, with little or no role for deliberate spatial attention.     

Gorillas in our midst: sustained inattentional blindness for dynamic events

With each eye fixation, we experience a richly detailed visual world. Yet recent work on visual integration and change direction reveals that we are surprisingly unaware of the details of our environment from one view to the next: we often do not detect large changes to objects and scenes ('change blindness'). Furthermore, without attention, we may not even perceive objects ('inattentional blindness'). Taken together, these findings suggest that we perceive and remember only those objects and details that receive focused attention. In this paper, we briefly review and discuss evidence for these cognitive forms of 'blindness'. We then present a new study that builds on classic studies of divided visual attention to examine inattentional blindness for complex objects and events in dynamic scenes. Our results suggest that the likelihood of noticing an unexpected object depends on the similarity of that object to other objects in the display and on how difficult the priming monitoring task is. Interestingly, spatial proximity of the critical unattended object to attended locations does not appear to affect detection, suggesting that observers attend to objects and events, not spatial positions. We discuss the implications of these results for visual representations and awareness of our visual environment.     

Keeping the end in mind: Preliminary brain and behavioral evidence for broad attention to endpoints in pre-linguistic infants

Infants must learn to carve events at their joints to best understand who is doing what to whom or whether an object or agent has reached its intended goal. Recent behavioral research demonstrates that infants do not see the world as a movie devoid of meaning, but rather as a series of sub-events that include agents moving in different manners along paths from sources to goals. This research uses behavioral and electrophysiological methods to investigate infants’ (10–14 months) attention to disruptions within relatively unfamiliar human action that does not rely on goal-objects to signal attainment (i.e., Olympic figure skating). Infants’ visual (Study 1, N = 48) and neurophysiological (Study 2, N = 21) responses to pauses at starting points, endpoints, and within-action locations were recorded. Both measures revealed differential responses to pauses at endpoints relative to pauses elsewhere in the action (i.e., starting point; within-action). Eye-tracking data indicated that infants’ visual attention was greater for events containing pauses at endpoints relative to events with pauses at starting points or within-actions. ERP activity reflecting perceptual processes in early-latency windows (<200 ms) and memory updating processes in long-latency windows (700−1000 ms) showed differential activation to disruptions at the end of a figure-skating action compared to other locations. Mid-latency windows (250−750 ms), in contrast, showed enhanced activation at frontal regions across conditions, suggesting electrophysiological resources may have been recruited to encode disruptions within unfamiliar dynamic human action. Combined, results hint at broad sensitivity to endpoints as a mechanism that supports infants’ proclivity for carving continuous and complex event streams into meaningful units. Findings have potential implications for language development as these units are mapped onto budding linguistic representations. We discuss empirical and methodological contributions for action perception and address potential merits and pitfalls of applying behavioral techniques in conjunction with brain-based measures to study infant development.     

Visual distraction increases the detection of an unexpected object in inattentional blindness

Distraction is typically thought to be detrimental to performance and concentration, and stimuli are classified as “distractions” if they take attention away from a primary task. However it has been shown that, under certain circumstances, distractors can also improve task performance. The current study extends this literature by exploring the role of a single discrete transient visual distracting event in increasing attention to an unexpected visual object in an inattentional blindness (IB) paradigm. Experiment 1 investigated the impact of a 48 ms visual distraction stimulus on rates of IB; a second experiment used a shortened, 16 ms visual distracting event. Both the long 48 ms and brief 16 ms distractors significantly reduced overall IB rates, by approximately 50% compared to a no distractor condition. Moreover, this reduction in IB is obtained independent of whether the visual distracting event was noted by the observer. Our findings demonstrate that a single discrete visual distraction can improve the detectability of an unexpected object in an IB task. Implications for theories of distributed attention in such tasks are discussed.     

Inattentional blindness for a noxious multimodal stimulus

Previous research has shown that people can miss salient stimuli outside the focus of their attention. This phenomenon, called inattentional blindness, typically is observed when people are given a task requiring them to focus their attention on one aspect of a complex visual scene. While participants are doing this task, an unexpected stimulus appears, and participants' awareness of it is tested shortly thereafter. In the present experiments, noxious bimodal stimuli were used as a test case to measure the strength of inattentional blindness. We tested whether participants would notice a person enter a scene and scratch her fingernails down a chalkboard (thus making a sound called a "gride"). A large proportion of participants failed to detect this event even when the noxious audio associated with it was strengthened and isolated in time from surrounding noises.     

Hypnotic blindness: a behavioral and experiential analysis

This research examined the influence of visual information on a decision task that subjects were administered during hypnotically suggested blindness. Real, hypnotizable subjects and simulating, unhypnotizable subjects were tested in two experiments. Experiment 1 focused on behavioral responses, and Experiment 2 focused on experiential reactions. In both experiments, the findings indicated that the behavioral responses of reals were influenced by visual information despite their reported blindness. The behavioral responses of reals and simulators were essentially similar. The experiential data in Experiment 2 provided information about the phenomenal nature of subjects' reported blindness. The experimental reactions of reals and simulators were essentially different. The research is discussed in terms of the issues that need to be considered in the development of a model of hypnotic 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.     

Leading questions and the eyewitness report

A total of 490 subjects, in four experiments, saw films of complex, fast-moving events, such as automobile accidents or classroom disruptions. The purpose of these experiments was to investigate how the wording of questions asked immediately after an event may influence responses to questions asked considerably later. It is shown that when the initial question contains either true presuppositions (e.g., it postulates the existence of an object that did exist in the scene) or false presuppositions (e.g., postulates the existence of an object that did not exist), the likelihood is increased that subjects will later report having seen the presupposed object. The results suggest that questions asked immediately after an event can introduce new—not necessarily correct—information, which is then added to the memorial representation of the event, thereby causing its reconstruction or alteration.     

Segmentation, attention and phenomenal visual objects

Issues concerning selective attention provoke new questions about visual segmentation, and vice-versa. We illustrate this by describing our recent work on grouping under conditions of inattention, on change blindness for background events and the residual processing of undetected background changes, on modal versus amodal completion in visual search, and the differential effects of these two forms of completion on attentional processes, and on attentional modulation of lateral interactions thought to arise in early visual cortex. Many of these results indicate that segmentation processes substantially constrain attentional processes, but the reverse influence is also apparent, suggesting an interactive architecture. We discuss how the 'proto-objects' revealed by studies of segmentation and attention (i.e. the segmented perceptual units which constrain selectivity) may relate to other object-based notions in cognitive science, and we wrestle with their relation to phenomenal visual awareness.     

Hypnotic blindness, awareness, and attribution

Examined whether performance on a spelling task would be influenced by visual information in the reported absence of hypnotized subjects' awareness of that information. Experiment 1 visually presented uncommon spellings of homophones to subjects before and during a suggestion for hypnotic blindness, and subsequently tested subjects' spelling of the homophones. Words presented during hypnotic blindness influenced subjects' spelling performance. Subjects' attributions of their performance did not involve awareness of the homophones. Experiment 2 used the nonexperiment methodology to examine the impact of demand characteristics and indicated that the performance attributions of subjects of Experiment 1 could not be explained in these terms. The discussion focuses on implicit perception in hypnotic blindness and on the relevance of attributions about behavioral performance on hypnotic phenomena.     

Inhibition of return exaggerates change blindness

Peripheral cues trigger attention shifts, which facilitate perceptual processing and enhance visual awareness. However, this facilitation is superseded by an inhibition of return (IOR) effect, which biases attention away from the cued location. While the link between facilitatory effects of visual attention and awareness is well established, no study has reported negative effects of spatial cueing on visual awareness. This failure is puzzling, given the claim that attention is a necessary precondition for awareness. If attention is necessary for awareness, inhibiting attention should also inhibit awareness. This leads to a slightly counterintuitive prediction: Spatial cueing will inhibit awareness at long cue–target latencies. This study shows that subliminal peripheral cues exaggerate change blindness at long cue–change latencies, demonstrating that IOR can suppress visual awareness of changes and suggesting that IOR can directly affect the contents of consciousness.     

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.     

Visual target detection is impaired at event boundaries

Boundaries between meaningful events are key moments in comprehending human action. At these points, viewers may focus on the event's contents at the expense of other information. We tested whether visual detection was impaired at those moments perceivers judged to be boundaries between events. Short animated football clips were used as stimulus material, and event boundaries were imposed by having the ball change possession. In a first experiment, we found that possession changes were perceived to be event boundaries. In a second experiment, participants were asked to keep track of 4 of 10 players and to watch for 120 ms probes appearing either at an event boundary or a nonboundary. Probe detection was less accurate at event boundaries. This result suggests that the segmentation of ongoing activity into events corresponds with the regulation of attention over time.     

Perception without attention: results of a new method.

Having found by the use of a new method for examining perception without attention that grouping and texture segregation do not seem to occur (see Mack, Tang, Tuma, Kahn, & Rock (1992) Cognitive Psychology, 24, we go on to ask what is perceived without attention using this new method. Our subjects receive only one inattention trial in a sequence of trials involving a visual distraction task. In addition to the distraction task in the inattention trial, subjects received a stimulus of which they had no prior knowledge or expectation and were questioned or tested directly afterward for their perception of that stimulus. Two subsequent trials containing test stimuli serve as within-subject controls. The results of a series of experiments indicate that the presence of one or more stimulus objects and their locations are preattentively perceived, as is their color, but shape is not. Because individual items are detected without attention, we conclude that perceptual organization is initially based on a principle in which connected regions of uniform stimulation are inferred to be discrete units (the principle of uniform connectedness). One striking, unexpected finding is that without attention many subjects have no awareness at all of the stimulus object, an effect we call inattentional blindness.     

Selective attention, inhibition for repeated events and hemispheric specialization

When two visual events appear consecutively in the same spatial location, our response to the second event is slower than to the first. This inhibition for repeated events may reflect a bias toward sampling novel locations, a bias useful for exploring visual space. It has been shown that the left hemisphere is more specialized in selective attentional processes than the right one. The aim of the present experiment was to test if this hemispheric specialization for selective attention may also affect the inhibition for repeated events. For this purpose, we asked 11 normal subjects to perform an identity-based discrimination task in which the target to be detected could appear alone or surrounded by flanking letters, in the left or in the right visual field. Results show that inhibition for repeated events is present only when selective attention is required and when the task is performed in the right specialized visual field.