Covert visual attention and extrafoveal information use during object identification

Three experiments are reported that examined the relationship between covert visual attention and a viewer's ability to use extrafoveal visual information during object identification. Subjects looked at arrays of four objects while their eye movements were recorded. Their task was to identify the objects in the array for an immediate probe memory test. During viewing, the number and location of objects visible during given fixations were manipulated. In Experiments 1 and 2, we found that multiple extrafoveal previews of an object did not afford any more benefit than a single extrafoveal preview, as assessed by means of time of fixation on the objects. In Experiment 3, we found evidence for a model in which extrafoveal information acquired during a fixation derives primarily from the location toward which the eyes will move next. The results are discussed in terms of their implications for the relationship between covert visual attention and extrafoveal information use, and a sequential attention model is proposed.     

Object–scene inconsistencies do not capture gaze: evidence from the flash-preview moving-window paradigm

In the present study, we investigated the influence of object-scene relationships on eye movement control during scene viewing. We specifically tested whether an object that is inconsistent with its scene context is able to capture gaze from the visual periphery. In four experiments, we presented rendered images of naturalistic scenes and compared baseline consistent objects with semantically, syntactically, or both semantically and syntactically inconsistent objects within those scenes. To disentangle the effects of extrafoveal and foveal object-scene processing on eye movement control, we used the flash-preview moving-window paradigm: A short scene preview was followed by an object search or free viewing of the scene, during which visual input was available only via a small gaze-contingent window. This method maximized extrafoveal processing during the preview but limited scene analysis to near-foveal regions during later stages of scene viewing. Across all experiments, there was no indication of an attraction of gaze toward object-scene inconsistencies. Rather than capturing gaze, the semantic inconsistency of an object weakened contextual guidance, resulting in impeded search performance and inefficient eye movement control. We conclude that inconsistent objects do not capture gaze from an initial glimpse of a scene.     

Identifying objects across saccades: effects of extrafoveal preview and flanker object context.

Two object-naming experiments explored the influence of extrafoveal preview information and flanker object context on transsaccadic object identification. Both the presence of an extrafoveal preview of the target object and the contextual constraint provided by extrafoveal flanker objects were found to influence the speed of object identification, but the latter effect occurred only when an extrafoveal preview of the target object was not presented prior to fixation. The context effect was found to be due to facilitation from related flankers rather than inhibition from unrelated flankers. No evidence was obtained for the hypothesis that constraining context can increase the usefulness of an extrafoveal preview of a to-be-fixated object.     

Are summary statistics enough? Evidence for the importance of shape in guiding visual search

Peripheral vision outside the focus of attention may rely on summary statistics. We used a gaze-contingent paradigm to directly test this assumption by asking whether search performance differed between targets and statistically-matched visualizations of the same targets. Four-object search displays included one statistically-matched object that was replaced by an unaltered version of the object during the first eye movement. Targets were designated by previews, which were never altered. Two types of statistically-matched objects were tested: One that maintained global shape and one that did not. Differences in guidance were found between targets and statistically-matched objects when shape was not preserved, suggesting that they were not informationally equivalent. Responses were also slower after target fixation when shape was not preserved, suggesting an extrafoveal processing of the target that again used shape information. We conclude that summary statistics must include some global shape information to approximate the peripheral information used during search.     

Role of spatial location in integration of pictorial information across saccades

Identification of a fixated object in a visual display is facilitated by integrating information from a preview of that object in the periphery with information extracted on the subsequent foveal fixation (Pollatsek, Rayner, & Collins, 1984). These experiments investigated the extent to which this integration is dependent on the spatial location of the information remaining constant. Two preview objects were presented in the periphery; Ss fixated that region and named a single target object that appeared in the same spatial location in which one of the two preview objects had been presented. Of primary interest was the facilitative effect when a preview object was identical to the target object as a function of whether they were in the same spatial location. The major finding was that although there was a small effect of switching, there was still a substantial preview benefit even when the location of the identical object switched. In addition, the switching effect did not interact with the level of identity between the preview and target. There was also a preview benefit in conditions in which there were no eye movements and the preview and target objects were at least 5 degrees apart. Thus, the data indicate that the process object identification is relatively insensitive to location information and that object information and location information are coded fairly independently.     

Effects of foveal priming and extrafoveal preview on object identification

The results of three different experiments suggested that the relation between an object in the fovea on fixation n and an object subsequently brought into the fovea on fixation n + 1 affects the time to identify the second object. In Experiment 1 we extended previous work by demonstrating that a previously seen related priming object speeded the time to name a target object even when a saccade intervened between the two objects. In Experiment 2 we replicated this result and further showed that the benefit on naming time was due to facilitation from the related object rather than inhibition from the unrelated object. In addition, naming of the target object was much slower in both experiments when there was not a peripheral preview of the target object on fixation n. However, because the effect of the foveal priming object was greater when the target was not present than when it was present, priming did not appear to make extraction of the extrafoveal information more efficient. In Experiment 3, fixation times were recorded while subjects looked at four objects in order to identify them. Fixation time on an object was shorter when a related object was fixated immediately before it, even though the four objects did not form a scene. The size of the facilitation was roughly comparable to that in several analogous experiments where scenes were used. The results suggest that the effects of a predictive scene context on object identification may be explainable in terms of an object-to-object or "intralevel" priming mechanism.     

Is attention necessary for object identification? Evidence from eye movements during the inspection of real-world scenes

Eye movements were recorded during the display of two images of a real-world scene that were inspected to determine whether they were the same or not (a comparative visual search task). In the displays where the pictures were different, one object had been changed, and this object was sometimes taken from another scene and was incongruent with the gist. The experiment established that incongruous objects attract eye fixations earlier than the congruous counterparts, but that this effect is not apparent until the picture has been displayed for several seconds. By controlling the visual saliency of the objects the experiment eliminates the possibility that the incongruency effect is dependent upon the conspicuity of the changed objects. A model of scene perception is suggested whereby attention is unnecessary for the partial recognition of an object that delivers sufficient information about its visual characteristics for the viewer to know that the object is improbable in that particular scene, and in which full identification requires foveal inspection.     

A behavioral task for the validation of a gaze-contingent simulated scotoma

Gaze-contingent displays provide a valuable method in visual research for controlling visual input and investigating its visual and cognitive processing. Although the body of research using gaze-contingent retinal stabilization techniques has grown considerably during the last decade, only few studies have been concerned with the reliability of the specific real-time simulations applied. Using a Landolt ring discrimination task, we present a behavioral validation of gaze-contingent central scotoma simulation in healthy observers. Importantly, behavioral testing is necessary to show whether the simulation impairs foveal processing of visual information. This test becomes even more crucial when researchers are faced with null results in a task performed with the scotoma, as compared with a control condition. It must be ruled out that the lack of behavioral effects results from a type II error caused by improper implementation before conclusions about foveal contributions to the given task may be drawn. In our experiment, the scotoma effectively prevented foveal processing of the visual stimuli, leading to significantly reduced response accuracies, as compared with unimpaired vision. Moreover, the final fixation at the time of the participants’ responses was placed close to the target position in the unimpaired condition, whereas the distance to the target was enhanced with the scotoma, indicating that the observers were not able to discriminate visual target stimuli from distractors, due to the scotoma. The present work presents a validated behavioral testing method for the efficiency of gaze-contingent scotoma simulations, including code for implementation. In addition, solutions for common methodological problems are discussed.     

Extrafoveal Processing in Categorical Search for Geometric Shapes: General Tendencies and Individual Variations

The paper addresses the capabilities and limitations of extrafoveal processing during a categorical visual search. Previous research has established that a target could be identified from the very first or without any saccade, suggesting that extrafoveal perception is necessarily involved. However, the limits in complexity defining the processed information are still not clear. We performed four experiments with a gradual increase of stimuli complexity to determine the role of extrafoveal processing in searching for the categorically defined geometric shape. The series of experiments demonstrated a significant role of extrafoveal processing while searching for simple two-dimensional shapes and its gradual decrease in a condition with more complicated three-dimensional shapes. The factors of objects’ spatial orientation and distractor homogeneity significantly influenced both reaction time and the number of saccades required to identify a categorically defined target. An analysis of the individual p-value distributions revealed pronounced individual differences in using extrafoveal analysis and allowed examination of the performance of each particular participant. The condition with the forced prohibition of eye movements enabled us to investigate the efficacy of covert attention in the condition with complicated shapes. Our results indicate that both foveal and extrafoveal processing are simultaneously involved during a categorical search, and the specificity of their interaction is determined by the spatial orientation of objects, type of distractors, the prohibition to use overt attention, and individual characteristics of the participants.     

Grasping of extrafoveal targets: A robotic model

We present a computational model of grasping of non-fixated (extrafoveal) target objects which is implemented on a robot setup, consisting of a robot arm with cameras and gripper. This model is based on the premotor theory of attention (Rizzolatti et al., 1994) which states that spatial attention is a consequence of the preparation of goal-directed, spatially coded movements (especially saccadic eye movements). In our model, we add the hypothesis that saccade planning is accompanied by the prediction of the retinal images after the saccade. The foveal region of these predicted images can be used to determine the orientation and shape of objects at the target location of the attention shift. This information is necessary for precise grasping. Our model consists of a saccade controller for target fixation, a visual forward model for the prediction of retinal images, and an arm controller which generates arm postures for grasping. We compare the precision of the robotic model in different task conditions, among them grasping (1) towards fixated target objects using the actual retinal images, (2) towards non-fixated target objects using visual prediction, and (3) towards non-fixated target objects without visual prediction. The first and second setting result in good grasping performance, while the third setting causes considerable errors of the gripper orientation, demonstrating that visual prediction might be an important component of eye–hand coordination. Finally, based on the present study we argue that the use of robots is a valuable research methodology within psychology.     

Priorities for representation: Task settings and object interaction both influence object memory

Following an active task, the memory representations for used and unused objects are different. However, it is not clear whether these differences arise due to prioritizing objects that are task-relevant, objects that are physically interacted with, or a combination of the two factors. The present study allowed us to tease apart the relative importance of task-relevance and physical manipulation on object memory. A paradigm was designed in which objects were either necessary to complete a task (target), moved out of the way (obstructing, but interacted with), or simply present in the environment (background). Participants’ eye movements were recorded with a portable tracker during the task, and they received a memory test on the objects after the task was completed. Results showed that manipulating an object is sufficient to change how information is extracted and retained from fixations, compared to background objects. Task-relevance provides an additional influence: information is accumulated and retained differently for manipulated target objects than manipulated obstructing objects. These findings demonstrate that object memory is influenced both by whether we physically interact with an object, and the relevance of that object to our behavioral goals.     

Semantically incongruent objects attract eye gaze when viewing scenes for change

Past research has shown that change detection performance is often more efficient for target objects that are semantically incongruent with a surrounding scene context than for target objects that are semantically congruent with the scene context. One account of these findings is that attention is attracted to objects for which the identity of the object conflicts with the meaning of the scene, perhaps as a violation of expectancies created by earlier recruitment of scene gist information. An alternative account of the performance benefit for incongruent objects is that attention is more apt to linger on incongruent objects, as perhaps identifying these objects is more difficult due to conflicting information from the scene context. In the current experiment, we present natural scenes in a change detection task while monitoring eye movements. We find that eye gaze is attracted to these objects relatively early during scene processing.     

Effect of background information on object identification

Previous research using briefly presented displays has indicated that objects in a coherent scene are easier to identify than are objects in incoherent backgrounds. Of interest is whether the identification of the target object depends on the identification of the scene or the identification of other diagnostic objects in the scene. Experiment 1 indicated objects are more difficult to identify when located in an "episodically" inconsistent background even when the same diagnostic objects are present in both inconsistent and consistent backgrounds. Experiment 2 demonstrated that the degree to which noncued (cohort) objects are consistent with the target object has no effect on the object identification task. Experiment 3 showed consistent episodic background information facilitated object identification and inconsistent episodic background information did not interfere relative to "nonsense" backgrounds roughly equated on visual characteristics. Implications for models of scene perception are discussed.     

Selective attention and the organization of visual information

Theories of visual attention deal with the limit on our ability to see (and later report) several things at once. These theories fall into three broad classes. Object-based theories propose a limit on the number of separate objects that can be perceived simultaneously. Discrimination-based theories propose a limit on the number of separate discriminations that can be made. Space-based theories propose a limit on the spatial area from which information can be taken up. To distinguish these views, the present experiments used small (less than 1 degree), brief, foveal displays, each consisting of two overlapping objects (a box with a line struck through it). It was found that two judgments that concern the same object can be made simultaneously without loss of accuracy, whereas two judgments that concern different objects cannot. Neither the similarity nor the difficulty of required discriminations, nor the spatial distribution of information, could account for the results. The experiments support a view in which parallel, preattentive processes serve to segment the field into separate objects, followed by a process of focal attention that deals with only one object at a time. This view is also able to account for results taken to support both discrimination-based and space-based theories.     

Cognitive control of fixation duration in visual search: The role of extrafoveal processing

Participants' eye movements were monitored in two visual search experiments that manipulated target-distractor similarity (high vs. low) as well as the availability of distractors for extrafoveal processing (Free-Viewing vs. No-Preview). The influence of the target-distractor similarity by preview manipulation on the distributions of first fixation and second fixation duration was examined by using a survival analysis technique which provided precise estimates of the timing of the first discernible influence of target-distractor similarity on fixation duration. We found a significant influence of target-distractor similarity on first fixation duration in normal visual search (Free Viewing) as early as 26–28 ms from the start of fixation. In contrast, the influence of target-distractor similarity occurred much later (199–233 ms) in the No-Preview condition. The present study also documented robust and fast acting extrafoveal and foveal preview effects. Implications for models of eye-movement control and visual search are discussed.     

靶刺激变换与情景信息属性对真实情景再认的影响

采用眼动研究范式,通过两个实验考察靶刺激变换与情景信息属性对情景再认的影响。实验一结果显示,靶刺激变换对情景再认、靶刺激所属兴趣区的凝视时间均有显著影响,这表明在情景再认过程中,观察者会有意识地搜索靶刺激,靶刺激具有诊断效应;实验二应用了知觉信息与语义信息重合和分离两种情景材料。结果显示,观察者对语义信息的首次注视次数显著多于知觉信息;观察者对知觉信息和语义信息分离条件下语义信息的首次注视时间显著长于重合条件下。这一结果提示,在情景识别过程中,语义信息具有注意优先性,但其优先性会受到知觉信息启动的干扰。     

Identification of objects in scenes: the role of scene background in object naming.

Research with brief presentations of scenes has indicated that scene context facilitates object identification. In the present experiments we used a paradigm in which an object in a scene is "wiggled"--drawing both attention and an eye fixation to itself--and then named. Thus the effect of scene context on object identification can be examined in a situation in which the target object is fixated and hence is fully visible. Experiment 1 indicated that a scene background that was episodically consistent with a target object facilitated the speed of naming. In Experiments 2 and 3, we investigated the time course of scene background information acquisition using display changes contingent on eye movements to the target object. The results from Experiment 2 were inconclusive; however, Experiment 3 demonstrated that scene background information present only on either the first or second fixation on a scene significantly affected naming time. Thus background information appears to be both extracted and able to affect object identification continuously during scene viewing.     

Preschoolers search for hidden objects

The issue of whether young children use spatio-temporal information (e.g., movement of objects through time and space) and/or contact-mechanical information (e.g., interaction between objects) to search for a hidden object was investigated. To determine whether one cue can have priority over the other, a dynamic event that put these cues into conflict was created, with only spatio-temporal information being valid. The 3-year-olds used in the study were found to use the valid spatio-temporal cue exclusively and seemed to ignore the contact-mechanical cue. Both search behavior and eye tracking during the event support the view of a sophisticated sensitivity to the validity of a cue in indicating a target’s hidden location.     

聋人阅读中的副中央凹视觉注意增强效应——来自消失文本的证据

为适应失聪后的复杂环境, 聋人视觉注意资源的空间分布发生改变, 这对聋人的阅读加工产生了影响。本研究尝试提出“聋人阅读中的副中央凹视觉注意增强效应”, 并采用消失文本范式考察这一效应对聋人读者副中央凹及中央凹处词汇信息视觉编码效率的影响。结果发现, 在词n+1短暂呈现时, 聋生快速编码副中央凹处文本信息的加工效率与其生理年龄匹配组相近, 高于阅读能力匹配组; 但在词n短暂呈现时, 聋生快速编码中央凹处文本信息的加工效率落后于健听控制组, 其词汇通达和总阅读效率均受阻。综上所述, 本研究证实了聋人阅读中的副中央凹视觉注意增强效应, 表现为副中央凹加工效率增强, 但中央凹加工效率受阻。