Egocentric metric representations in peripersonal space: A bridge between motor resources and spatial memory

Research on visuospatial memory has shown that egocentric (subject-to-object) and allocentric (object-to-object) reference frames are connected to categorical (non-metric) and coordinate (metric) spatial relations, and that motor resources are recruited especially when processing spatial information in peripersonal (within arm reaching) than extrapersonal (outside arm reaching) space. In order to perform our daily-life activities, these spatial components cooperate along a continuum from recognition-related (e.g., recognizing stimuli) to action-related (e.g., reaching stimuli) purposes. Therefore, it is possible that some types of spatial representations rely more on action/motor processes than others. Here, we explored the role of motor resources in the combinations of these visuospatial memory components. A motor interference paradigm was adopted in which participants had their arms bent behind their back or free during a spatial memory task. This task consisted in memorizing triads of objects and then verbally judging what was the object: (1) closest to/farthest from the participant (egocentric coordinate); (2) to the right/left of the participant (egocentric categorical); (3) closest to/farthest from a target object (allocentric coordinate); and (4) on the right/left of a target object (allocentric categorical). The triads appeared in participants' peripersonal (Experiment 1) or extrapersonal (Experiment 2) space. The results of Experiment 1 showed that motor interference selectively damaged egocentric-coordinate judgements but not the other spatial combinations. The results of Experiment 2 showed that the interference effect disappeared when the objects were in the extrapersonal space. A third follow-up study using a within-subject design confirmed the overall pattern of results. Our findings provide evidence that motor resources play an important role in the combination of coordinate spatial relations and egocentric representations in peripersonal space.     

Categorical perception of familiar objects

We report three experiments where the categorical perception of familiar, three-dimensional objects was investigated. A continuum of shape change between 15 pairs of objects was created and the images along the continuum were used as stimuli. In Experiment 1 participants were first required to discriminate pairs of images of objects that lay along the shape continuum. Then participants were asked to classify each morph-image into one of two pre-specified classes. We found evidence for categorical perception in some but not all of our object pairs. In Experiment 2 we varied the viewpoint of the objects in the discrimination task and found that effects of categorical perception generalized across changes in view. In Experiment 3 similarity ratings for each object pair were collected. These similarity scores correlated with the degree of perceptual categorization found for the object pairs. Our findings suggest that some familiar objects are perceived categorically and that categorical perception is closely tied to inter-object perceptual similarity.     

Oculomotion mediates attentional guidance toward temporarily close objects

Previous research has identified multiple features of individual objects that are capable of guiding visual attention. However, in dynamic multi-element displays not only individual object features but also changing spatial relations between two or more objects might signal relevance. Here we report a series of experiments that investigated the hypothesis that reduced inter-object spacing guides visual attention toward the corresponding objects. Our participants discriminated between different probes that appeared on moving objects while we manipulated spatial proximity between the objects at the moment of probe onset. Indeed, our results confirm that there is a bias toward temporarily close objects, which persists even when such a bias is harmful for the actual task (Experiments 1a and 1b). Remarkably, this bias is mediated by oculomotor processes. Controlling for eye-movements reverses the pattern of results (Experiment 2a), whereas the location of the gaze tends toward the temporarily close objects under free viewing conditions (Experiment 2b). Taken together, our results provide insights into the interplay of attentional and oculomotor processes during dynamic scene processing. Thereby, they also add to the growing body of evidence showing that within dynamic perception, attentional and oculomotor processes act conjointly and are hardly separable.     

Distinguishing the effects of action relations and scene context on object perception

Objects are rarely viewed in isolation, and so how they are perceived is influenced by the context in which they are viewed and their interaction with other objects (e.g., whether objects are colocated for action). We investigated the combined effects of action relations and scene context on an object decision task. Experiment 1 investigated whether the benefit for positioning objects so that they interact is enhanced when objects are viewed within contextually congruent scenes. The results indicated that scene context influenced perception of nonaction-related objects (e.g., monitor and keyboard), but had no effect on responses to action-related objects (e.g., bottle and glass) that were processed more rapidly. In Experiment 2, we reduced the saliency of the object stimuli and found that, under these circumstances, scene context influenced responses to action-related objects. We discuss the data in terms of relatively late effects of scene processing on object perception.     

Scene perception: Detecting and judging objects undergoing relational violations

Five classes of relations between an object and its setting can characterize the organization of objects into real-world scenes. The relations are (1) Interposition (objects interrupt their background), (2) Support (objects tend to rest on surfaces), (3) Probability (objects tend to be found in some scenes but not others), (4) Position (given an object is probable in a scene, it often is found in some positions and not others), and (5) familiar Size (objects have a limited set of size relations with other objects). In two experiments subjects viewed brief (150 msec) presentations of slides of scenes in which an object in a cued location in the scene was either in a normal relation to its background or violated from one to three of the relations. Such objects appear to (1) have the background pass through them, (2) float in air, (3) be unlikely in that particular scene, (4) be in an inappropriate position, and (5) be too large or too small relative to the other objects in the scene. In Experiment I, subjects attempted to determine whether the cued object corresponded to a target object which had been specified in advance by name. With the exception of the Interposition violation, violation costs were incurred in that the detection of objects undergoing violations was less accurate and slower than when those same objects were in normal relations to their setting. However, the detection of objects in normal relations to their setting (innocent bystanders) was unaffected by the presence of another object undergoing a violation in that same setting. This indicates that the violation costs were incurred not because of an unsuccessful elicitation of a frame or schema for the scene but because properly formed frames interfered with (or did not facilitate) the perceptibility of objects undergoing violations. As the number of violations increased, target detectability generally decreased. Thus, the relations were accessed from the results of a single fixation and were available sufficiently early during the time course of scene perception to affect the perception of the objects in the scene. Contrary to expectations from a bottom-up account of scene perception, violations of the pervasive physical relations of Support and Interposition were not more disruptive on object detection than the semantic violations of Probability, Position and Size. These are termed semantic because they require access to the referential meaning of the object. In Experiment II, subjects attempted to detect the presence of the violations themselves. Violations of the semantic relations were detected more accurately than violations of Interposition and at least as accurately as violations of Support. As the number of violations increased, the detectability of the incongruities between an object and its setting increased. These results provide converging evidence that semantic relations can be accessed from the results of a single fixation. In both experiments information about Position was accessed at least as quickly as information on Probability. Thus in Experiment I, the interference that resulted from placing a fire hydrant in a kitchen was not greater than the interference from placing it on top of a mail ? in a street scene. Similarly, violations of Probability in Experiment II were not more detectable than violations of Position. Thus, the semantic relations which were accessed included information about the detailed interactions among the objects—information which is more specific than what can be inferred from the general setting. Access to the semantic relations among the entities in a scene is not deferred until the completion of spatial and depth processing and object identification. Instead, an object's semantic relations are accessed simultaneously with its physical relations as well as with its own identification.     

Gaze cues influence the allocation of attention in natural scene viewing

In two experiments we examined whether the allocation of attention in natural scene viewing is influenced by the gaze cues (head and eye direction) of an individual appearing in the scene. Each experiment employed a variant of the flicker paradigm in which alternating versions of a scene and a modified version of that scene were separated by a brief blank field. In Experiment 1, participants were able to detect the change made to the scene sooner when an individual appearing in the scene was gazing at the changing object than when the individual was absent, gazing straight ahead, or gazing at a nonchanging object. In addition, participants' ability to detect change deteriorated linearly as the changing object was located progressively further from the line of regard of the gazer. Experiment 2 replicated this change detection advantage of gaze-cued objects in a modified procedure using more critical scenes, a forced-choice change/no-change decision, and accuracy as the dependent variable. These findings establish that in the perception of static natural scenes and in a change detection task, attention is preferentially allocated to objects that are the target of another's social attention.     

Gaze cues influence the allocation of attention in natural scene viewing

In two experiments we examined whether the allocation of attention in natural scene viewing is influenced by the gaze cues (head and eye direction) of an individual appearing in the scene. Each experiment employed a variant of the flicker paradigm in which alternating versions of a scene and a modified version of that scene were separated by a brief blank field. In Experiment 1, participants were able to detect the change made to the scene sooner when an individual appearing in the scene was gazing at the changing object than when the individual was absent, gazing straight ahead, or gazing at a nonchanging object. In addition, participants' ability to detect change deteriorated linearly as the changing object was located progressively further from the line of regard of the gazer. Experiment 2 replicated this change detection advantage of gaze-cued objects in a modified procedure using more critical scenes, a forced-choice change/no-change decision, and accuracy as the dependent variable. These findings establish that in the perception of static natural scenes and in a change detection task, attention is preferentially allocated to objects that are the target of another's social attention.     

Exogenous attention differentially modulates the processing of categorical and coordinate spatial relations

Carrasco and her colleagues have suggested that exogenous attention reduces the size of receptive fields at an attended location (Gobell & Carrasco, 2005; Yeshurun & Carrasco, 1998, 2000). Based on the hypothesis that categorical and coordinate spatial relations are more efficiently processed by smaller and larger receptive fields, respectively, we predicted that exogenous attention would be more beneficial to the processing of categorical spatial relations than coordinate spatial relations while it would disrupt the processing of coordinate spatial relations. To test these hypotheses, participants were tested using a variant of Posner's (1980) attentional cueing paradigm. Exogenous attention produced larger facilitative effects on categorical spatial processing than on coordinate spatial processing at a short cue-target stimulus onset asynchrony (100 ms, Experiment 1, N = 28), and this result was replicated regardless of cue size in Experiment 2 (N = 24). When the coordinate judgment was sufficiently difficult, exogenous attention disrupted the processing of coordinate spatial relations (Experiment 3, N = 28). These findings indicate that exogenous attention can differentially modulate the processing of categorical and coordinate spatial relations.     

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。     

语言标签和自我关联对新颖客体类别知觉的影响

类别知觉(Categorical perception)是人类最基本的认知活动之一, 探讨语言对类别知觉的影响是心理语言学领域的热门话题之一。在这个研究的3个实验中, 分别在高、低不同的语言标签表征强度下、高、低不同的客体自我关联程度下观察新颖客体类别知觉的过程。研究发现, 语言标签表征程度的增强可促进新颖客体类别知觉的右视野优势效应; 客体与自我关联程度的提高会促进左、右视野的类别知觉效应; 语言标签的表征程度和客体与自我关联程度同时增强时, 语言标签的作用依旧表现出来, 但与自我关联的影响产生权衡分配, 且其影响力并不足以产生右视野优势效应。     

Detection and Identification of Change in Naturalistic Scenes

Research using change detection paradigms has demonstrated that only limited scene information remains available for conscious report following initial inspection of a scene. Previous researchers have found higher change identification rates for deletions of parts of objects in line drawings of scenes than additions. Other researchers, however, have found an asymmetry in the opposite direction for addition/deletion of whole objects in line drawings of scenes. Experiment 1 investigated subjects' accuracy in detecting and identifying changes made to successive views of high quality photographs of naturalistic scenes that involved the addition and deletion of objects, colour changes to objects, and changes to the spatial location of objects. Identification accuracy for deletions from scenes was highest, with lower identification rates for object additions and colour changes, and the lowest rates for identification of location changes. Data further suggested that change identification rates for the presence/absence of objects were a function of the number of identical items present in the scene. Experiment 2 examined this possibility further, and also investigated whether the higher identification rates for deletions found in Experiment 1 were found for changes involving whole objects or parts of objects. Results showed higher identification rates for deletions, but only where a unique object was deleted from a scene. The presence of an identical object in the scene abolished this deletion identification advantage. Results further showed that the deletion/addition asymmetry occurs both when the objects are parts of a larger object and when they are entire objects in the scene.     

Effects of spatial configurations on visual change detection: An account of bias changes

In order to determine whether people encode spatial configuration information when encoding visual displays, in four experiments, we investigated whether changes in task-irrelevant spatial configuration information would influence color change detection accuracy. In a change detection task, when objects in the test display were presented in new random locations, rather than identical or different locations preserving the overall configuration, participants were more likely to report that the colors had changed. This consistent bias across four experiments suggested that people encode task-irrelevant spatial configuration along with object information. Experiment 4 also demonstrated that only a low-false-alarm group of participants effectively bound spatial configuration information to object information, suggesting that these types of binding processes are open to strategic influences.     

Categorical perception of relative orientation in visual object recognition

The purpose of the present investigation was to determine whether the orientation between an object's parts is coded categorically for object recognition and physical discrimination. In three experiments, line drawings of novel objects in which the relative orientation of object parts varied by steps of 30 degrees were used. Participants performed either an object recognition task, in which they had to determine whether two objects were composed of the same set of parts, or a physical discrimination task, in which they had to determine whether two objects were physically identical. For object recognition, participants found it more difficult to compare the 0 degrees and 30 degrees versions and the 90 degrees and 60 degrees versions of an object than to compare the 30 degrees and 60 degrees versions, but only at an extended interstimulus interval (ISI). Categorical coding was also found in the physical discrimination task. These results suggest that relative orientation is coded categorically for both object recognition and physical discrimination, although metric information appears to be coded as well, especially at brief ISIs.     

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.     

Top-down attentional modulation of spatial frequency processing in scene perception

Recent evidence suggests that spatial frequency (SF) processing of simple and complex visual patterns is flexible. The use of spatial scale in scene perception seems to be influenced by people's expectations. However as yet there is no direct evidence for top-down attentional effects on flexible scale use in scene perception. In two experiments we provide such evidence. We presented participants with low- and high-pass SF filtered scenes and cued their attention to the relevant scale. In Experiment 1 we subsequently presented them with hybrid scenes (both low- and high-pass scenes present). We observed that participants reported detecting the cued component of hybrids. To explore if this might be due to decision biases, in Experiment 2, we replaced hybrids with images containing meaningful scenes at uncued SFs and noise at the cued SFs (invalid cueing). We found that participants performed poorly on invalid cueing trials. These findings are consistent with top-down attentional modulation of early spatial frequency processing in scene perception.     

Attention and perceptual implicit memory: effects of selective versus divided attention and number of visual objects

Extant research presents conflicting results on whether manipulations of attention during encoding affect perceptual priming. Two suggested mediating factors are type of manipulation (selective vs divided) and whether attention is manipulated across multiple objects or within a single object. Words printed in different colors (Experiment 1) or flanked by colored blocks (Experiment 2) were presented at encoding. In the full-attention condition, participants always read the word, in the unattended condition they always identified the color, and in the divided-attention conditions, participants attended to both word identity and color. Perceptual priming was assessed with perceptual identification and explicit memory with recognition. Relative to the full-attention condition, attending to color always reduced priming. Dividing attention between word identity and color, however, only disrupted priming when these attributes were presented as multiple objects (Experiment 2) but not when they were dimensions of a common object (Experiment 1). On the explicit test, manipulations of attention always affected recognition accuracy.     

Egocentric/allocentric and coordinate/categorical haptic encoding in blind people

In this research, the impact of visual experience on the capacity to use egocentric (body-centered) and allocentric (object-centered) representations in combination with categorical (invariant non-metric) and coordinate (variable metric) spatial relations was examined. Participants memorized through haptic (congenitally blind, adventitiously blind, and blindfolded) and haptic + visual (sighted) exploration triads of 3D objects and then they were asked to judge: "which object was closest/farthest to you?" (egocentric-coordinate); "which object was on your left/right?" (egocentric-categorical); "which object was closest/farthest to a target object (e.g., cone)?" (allocentric-coordinate); "which object was on the left/right of the target object (e.g., cone)?" (allocentric-categorical). The results showed a slowdown in processing time when congenitally blind people provided allocentric-coordinate judgments and adventitiously blind people egocentric-categorical judgments. Moreover, in egocentric judgments, adventitiously blind participants were less accurate than sighted participants. However, the overall performance was quite good and this supports the idea that the differences observed are more quantitative than qualitative. The theoretical implications of these results are discussed.     

Attentional allocation during the perception of scenes

Semantic influences on attention during the 1st fixation on a scene were explored in 3 experiments. Subjects viewed briefly presented scenes; following scene presentation, a spatial probe was presented at the location of an object whose identity was consistent or inconsistent with the scene category. Responses to the probe served as an index of attention. The results of Experiment 1 suggest that within approximately 150 ms of scene onset, subjects attend preferentially to inconsistent objects. The results of Experiment 2, in which additional scene durations were used, confirm the presence of an inconsistent-object advantage that emerges within approximately 150 ms. Finally, the results of Experiment 3 demonstrate that the inconsistent-object advantage does not reflect strategic allocation of attention to likely probe locations. Implications of the results for scene perception and exploration are discussed.     

Object detection in natural scenes: Independent effects of spatial and category-based attention

Humans are remarkably efficient in detecting highly familiar object categories in natural scenes, with evidence suggesting that such object detection can be performed in the (near) absence of attention. Here we systematically explored the influences of both spatial attention and category-based attention on the accuracy of object detection in natural scenes. Manipulating both types of attention additionally allowed for addressing how these factors interact: whether the requirement for spatial attention depends on the extent to which observers are prepared to detect a specific object category—that is, on category-based attention. The results showed that the detection of targets from one category (animals or vehicles) was better than the detection of targets from two categories (animals and vehicles), demonstrating the beneficial effect of category-based attention. This effect did not depend on the semantic congruency of the target object and the background scene, indicating that observers attended to visual features diagnostic of the foreground target objects from the cued category. Importantly, in three experiments the detection of objects in scenes presented in the periphery was significantly impaired when observers simultaneously performed an attentionally demanding task at fixation, showing that spatial attention affects natural scene perception. In all experiments, the effects of category-based attention and spatial attention on object detection performance were additive rather than interactive. Finally, neither spatial nor category-based attention influenced metacognitive ability for object detection performance. These findings demonstrate that efficient object detection in natural scenes is independently facilitated by spatial and category-based attention.