Attentive tracking of objects versus substances

Recent research in vision science, infant cognition, and word learning suggests a special role for the processing of discrete objects. But what counts as an object? Answers to this question often depend on contrasting object-based processing with the processing of spatial areas or unbound visual features. In infant cognition and word learning, though, another salient contrast has been between rigid cohesive objects and nonsolid substances. Whereas objects may move from one location to another, a nonsolid substance must pour from one location to another. In the study reported here, we explored whether attentive tracking processes are sensitive to dynamic information of this type. Using a multiple-object tracking task, we found that subjects could easily track four items in a display of eight identical unpredictably moving entities that moved as discrete objects from one location to another, but could not track similar entities that noncohesively "poured" from one location to another-even when the items in both conditions followed the same trajectories at the same speeds. Other conditions revealed that this inability to track multiple "substances" stemmed not from violations of rigidity or cohesiveness per se, because subjects were able to track multiple noncohesive collections and multiple nonrigid deforming objects. Rather, the impairment was due to the dynamic extension and contraction during the substancelike motion, which rendered the location of the entity ambiguous. These results demonstrate a convergence between processes of midlevel adult vision and infant cognition, and in general help to clarify what can count as a persisting dynamic object of attention.     

Multiple object tracking in people with Williams syndrome and in normally developing children

Multiple object tracking is hypothesized to utilize visual indexes, which may provide rapid, parallel access to a limited number of visual objects, thereby supporting a variety of spatial tasks. We examined whether faulty indexing might play a role in the severe visuospatial deficits found in Williams syndrome. We asked observers to track from one to four targets in a display of eight identical objects. Objects remained stationary (static condition) or moved randomly and independently (moving condition) for 6 s, after which observers pointed to the objects they thought were targets. People with Williams syndrome were impaired in the moving condition, but not the static condition, compared with mental-age-matched control participants. Normal children who were younger than the mental-age-matched control children did not show the same profile as individuals with Williams syndrome, which suggests that the difference between the tasks in Williams syndrome did not reflect simple developmental immaturity. Error analysis revealed that all groups had "slippery" indexes, falsely identifying target neighbors, and further suggested that people with Williams syndrome deploy fewer indexes than do people without this disorder.     

Looking ahead: Attending to anticipatory locations increases perception of control

When people manipulate a moving object, such as writing with a pen or driving a car, they experience their actions as intimately related to the object’s motion, that is they perceive control. Here, we tested the hypothesis that observers would feel more control over a moving object if an unrelated task drew attention to a location to which the object subsequently moved. Participants steered an object within a narrow path and discriminated the color of a flash that appeared briefly close to the object. Across two experiments, participants provided higher ratings of perceived control when an object moved over a flash’s location than when an object moved away from a flash’s location. This result suggests that we use the location of spatial attention to determine the perception of control. If an object goes where we are attending, we feel like we made it go there.     

The distribution of attention within objects in multiple-object scenes: prioritization by spatial probabilities and a center bias

This study investigates how the attentional distribution within objects is affected by spatial probabilities, bias toward objects' centers (Alvarez & Scholl, 2005), and object motion. In a multiple-object tracking task, observers tracked line objects while simultaneously detecting probes appearing on the objects. Experiments 1 and 2 manipulated the probabilities of probes appearing at the centers and ends of objects. Overall, probe detection was better at centers than at ends, but it was also affected by probe location probabilities; when probe locations were 100% certain, the center advantage was eliminated. Experiment 3 manipulated rotational, translational, and size-change components of object motion. The center advantage still occurred with stationary objects, and its magnitude was not affected by different motion types. These results indicate that attention is biased toward the centers of objects in multiple-object scenes, both for stationary and moving objects. They also imply that attentional prioritizations based on spatial probabilities can accompany moving objects.     

Interacting with objects compresses environmental representations in spatial memory

People perceive individual objects as being closer when they have the ability to interact with the objects than when they do not. We asked how interaction with multiple objects impacts representations of the environment. Participants studied multiple-object layouts, by manually exploring or simply observing each object, and then drew a scaled version of the environment (Exp. 1) or reconstructed a copy of the environment and its boundaries (Exp. 2) from memory. The participants who interacted with multiple objects remembered these objects as being closer together and reconstructed smaller environment boundaries than did the participants who looked without touching. These findings provide evidence that action-based perceptual distortions endure in memory over a moving observer’s multiple interactions, compressing not only representations between touched objects, but also untouched environmental boundaries.     

身份交换对多身份追踪表现的影响

本研究探讨了身份交换对多身份追踪表现的影响。实验1和实验2分别考察了全部报告法和部分报告法下身份交换对多身份追踪表现的具体影响。结果均发现, 身份交换对身份−位置绑定干扰程度越大, 位置追踪和身份识别容量也均越低, 但位置容量始终高于身份容量, 并且这些特性在不同追踪负荷上相同。此外, 部分报告法比全部报告法更具有容量测量优势。实验3则进一步从听觉通道上控制了语音复述对当前任务的干扰, 所得结果仍支持实验1和实验2。这表明, 身份交换对多身份追踪的干扰机制是身份−位置绑定机制受到损害, 而非语音复述的作用。     

Constraints on Multiple Object Tracking in Williams Syndrome: How Atypical Development Can Inform Theories of Visual Processing

The ability to track moving objects is a crucial skill for performance in everyday spatial tasks. The tracking mechanism depends on representation of moving items as coherent entities, which follow the spatiotemporal constraints of objects in the world. In the present experiment, participants tracked 1 to 4 targets in a display of 8 identical objects. Objects moved randomly and independently (moving condition), passed behind an invisible bar (occluded condition), or momentarily disappeared by shrinking (implosion condition). Scholl and Pylyshyn (1999) found that adults can track entities under the moving and occluded conditions, but not under implosion. This finding suggests that the tracking mechanism is constrained by the spatiotemporal properties of physical objects as they move in the world. In the present study, we adapt these conditions to investigate whether this constraint holds for people with severe spatial impairments associated with Williams syndrome (WS). In Experiment 1, we compare the performance of individuals with WS and typically developing (TD) adults. TD adults replicated Scholl and Pylyshyn’s findings; performance was no different between the moving and occluded conditions but was worse under implosion. People with WS had reduced tracking capacity but demonstrated the same pattern across conditions. In Experiment 2, we tested TD 4-, 5-, and 7-year-olds. People with WS performed at a level that fell between TD 4- and 5-year-olds. These results suggest that the multiple object tracking system in WS operates under the same object-based constraints that hold in typical development.     

Age-related changes in attentional tracking of multiple moving objects

In a multiple-object tracking (MOT) task, young and older adults attentively tracked a subset of 10 identical, randomly moving disks for several seconds, and then tried to identify those disks that had comprised the subset. Young adults who habitually played video games performed significantly better than those who did not. Compared to young subjects (mean age = 20.6 years) with whom they were matched for video game experience, older subjects (mean age = 75.3 years) showed much reduced ability to track multiple moving objects, particularly with faster movement or longer tracking times. Control measurements with stationary disks show that the age-related decline in MOT was not caused by a general change in memory per se. To generate an item-wise performance measure, we examined older subjects' proportion correct according to the serial order in which individual disks were identified. Correct identification of target disks declined with the order in which targets were reported, suggesting that attentional tracking produced graded, rather than all-or-none, outcomes.     

The role of location and motion information in the tracking and recovery of moving objects

Observers in a multiple object tracking task can track about four to five independently moving targets among several moving distractors, even if all of the stimuli disappear for a 300-msec gap. How observers reacquire targets following such a gap reveals what kind of information they can maintain for targets. Previous research has suggested that participants maintain minimal information about a set of moving objects--namely, just their present spatial locations. We report five new experiments that demonstrate retention of location information for at least four objects, and extrapolated motion information for around two objects.     

Infants' representations of three-dimensional occluded objects

Infants' ability to represent objects has received significant attention from the developmental research community. With the advent of eye-tracking technology, detailed analysis of infants' looking patterns during object occlusion have revealed much about the nature of infants' representations. The current study continues this research by analyzing infants' looking patterns in a novel manner and by comparing infants' looking at a simple display in which a single three-dimensional (3D) object moves along a continuous trajectory to a more complex display in which two 3D objects undergo trajectories that are interrupted behind an occluder. Six-month-old infants saw an occlusion sequence in which a ball moved along a linear path, disappeared behind a rectangular screen, and then a ball (ball-ball event) or a box (ball-box event) emerged at the other edge. An eye-tracking system recorded infants' eye-movements during the event sequence. Results from examination of infants' attention to the occluder indicate that during the occlusion interval infants looked longer to the side of the occluder behind which the moving occluded object was located, shifting gaze from one side of the occluder to the other as the object(s) moved behind the screen. Furthermore, when events included two objects, infants attended to the spatiotemporal coordinates of the objects longer than when a single object was involved. These results provide clear evidence that infants' visual tracking is different in response to a one-object display than to a two-object display. Furthermore, this finding suggests that infants may require more focused attention to the hidden position of objects in more complex multiple-object displays and provides additional evidence that infants represent the spatial location of moving occluded objects.     

Tracking objects that move where they are headed

Previous work has demonstrated that the ability to keep track of moving objects is improved when the objects have unique visual features, such as color or shape. In the present study, we investigated how orientation information is used during the tracking of objects. Orientation is an interesting feature to explore in moving objects because it is directional and is often informative of the direction of motion. Most objects move forward, in the direction they are oriented. In the present experiments, participants tracked a subset of moving isosceles triangles whose orientations were constant, related, or unrelated to the direction of motion. In the standard multiple object tracking (MOT) task, tracking performance improved when orientations were unique and remained constant, but not when orientation and direction of motion were aligned. In the target recovery task, in which MOT was interrupted by a brief blanking of the display, performance did improve when orientation and direction were aligned. In the final experiment, results showed that orientation was not used before the blank to predict future target locations, but was instead used after the blank. We concluded that people use orientation to compare a stored representation to target position for recovery of lost targets.     

Developmental profiles for multiple object tracking and spatial memory: typically developing preschoolers and people with Williams syndrome

The ability to track moving objects, a crucial skill for mature performance on everyday spatial tasks, has been hypothesized to require a specialized mechanism that may be available in infancy (i.e. indexes). Consistent with the idea of specialization, our previous work showed that object tracking was more impaired than a matched spatial memory task in individuals with Williams syndrome (WS), a genetic disorder characterized by severe visuo‐spatial impairment. We now ask whether this unusual pattern of performance is a reflection of general immaturity or of true abnormality, possibly reflecting the atypical brain development in WS. To examine these two possibilities, we tested typically developing 3‐ and 4‐year‐olds and people with WS on multiple object tracking (MOT) and memory for static spatial location. The maximum number of objects that could be correctly tracked or remembered (estimated from the k‐statistic) showed similar developmental profiles in typically developing 3‐ and 4‐year‐old children, but the WS profile differed from either age group. People with WS could track more objects than 3‐year‐olds, and the same number as 4‐year‐olds, but they could remember the locations of more static objects than both 3‐ and 4‐year‐olds. Combining these data with those from our previous studies, we found that typically developing children show increases in the number of objects they can track or remember between the ages of 3 and 6, and these increases grow in parallel across the two tasks. In contrast, object tracking in older children and adults with WS remains at the level of 4‐year‐olds, whereas the ability to remember multiple locations of static objects develops further. As a whole, the evidence suggests that MOT and memory for static location develop in tandem typically, but not in WS. Atypical development of the parietal lobe in people with WS could play a causal role in the abnormal, uneven pattern of performance in WS. This interpretation is consistent with the idea that multiple object tracking engages different mechanisms from those involved in memory for static object location, and that the former can be particularly disrupted by atypical development.     

多身份追踪中基于表情特征的分组效应

探讨了表情因素作为身份特征对多身份追踪中分组效应的影响。采用多身份追踪范式, 8个客体为表情图片(正性、负性、中性)其中4个为目标, 对45名被试进行了有无眉毛线索对追踪表现影响的测查。实验条件分别为：目标表情与非目标表情完全不相同组(4水平, 简称分组)、目标表情与非目标表情都由两种相同数量的表情混合组成(3水平, 简称配对)与基线组(8个客体表情相同)。发现分组水平的成绩显著优于基线组, 配对水平的成绩显著低于基线组, 并表现出了负性表情的追踪优势; 另外, 有无眉毛线索对追踪表现无显著影响。这一结果说明多身份追踪中存在基于表情特征的分组效应, 负性表情的分组知觉高于正性表情。     

Close encounters of the distracting kind: Identifying the cause of visual tracking errors

Why can we track only so many objects? We addressed this question by asking when and how tracking errors emerge. To test the hypothesis that many tracking errors are target/nontarget confusions emerging from close encounters, we compared standard multiple-object tracking trials with trials on which a nontarget turned a random color whenever it approached within 4° of a target. This manipulation significantly improved performance by alleviating the correspondence challenge of a close encounter. Two control experiments showed that color change benefits were not merely due to target recovery. Follow-up experiments demonstrated that color change benefits did not accrue monotonically with distance but, instead, seemed to obey a step function; and an additional experiment demonstrated that, without color changes, the frequency of close encounters predicts tracking performance. Taken together, these experiments suggest that uncertainty about target location imposes the primary constraint on tracking, at times causing errors by leading to confusions between targets and nontargets.     

Comparing eye movements during position tracking and identity tracking: No evidence for separate systems

There is an ongoing debate as to whether people track multiple moving objects in a serial fashion or with a parallel mechanism. One recent study compared eye movements when observers tracked identical objects (Multiple Object Tracking—MOT task) versus when they tracked the identities of different objects (Multiple Identity Tracking—MIT task). Distinct eye-movement patterns were found and attributed to two separate tracking systems. However, the same results could be caused by differences in the stimuli viewed during tracking. In the present study, object identities in the MIT task were invisible during tracking, so observers performed MOT and MIT tasks with identical stimuli. Observer were able to track either position and identity depending on the task. There was no difference in eye movements between position tracking and identity tracking. This result suggests that, while observers can use different eye-movement strategies in MOT and MIT, it is not necessary.     

Grouping and trajectory storage in multiple object tracking: impairments due to common item motions

In our natural viewing, we notice that objects change their locations across space and time. However, there has been relatively little consideration of the role of motion information in the construction and maintenance of object representations. We investigated this question in the context of the multiple object tracking (MOT) paradigm, wherein observers must keep track of target objects as they move randomly amid featurally identical distractors. In three experiments, we observed impairments in tracking ability when the motions of the target and distractor items shared particular properties. Specifically, we observed impairments when the target and distractor items were in a chasing relationship or moved in a uniform direction. Surprisingly, tracking ability was impaired by these manipulations even when observers failed to notice them. Our results suggest that differentiable trajectory information is an important factor in successful performance of MOT tasks. More generally, these results suggest that various types of common motion can serve as cues to form more global object representations even in the absence of other grouping cues.     

Body- and environmental-stabilized processing of spatial knowledge

In 5 experiments, the authors examined the perceptual and cognitive processes used to track the locations of objects during locomotion. Participants learned locations of 9 objects on the outer part of a turntable from a single viewpoint while standing in the middle of the turntable. They subsequently pointed to objects while facing the learning heading and a new heading, using imagined headings that corresponded to their current actual body heading and the other actual heading. Participants in 4 experiments were asked to imagine that the objects moved with them as they turned and were shown or only told that the objects would move with them; in Experiment 5, participants were shown that objects could move with them but were asked to ignore this as they turned. Results showed that participants tracked object locations as though the objects moved with them when shown but not when told about the consequences of their locomotion. Once activated, this processing mode could not be suppressed by instructions. Results indicated that people process object locations in a body- or an environment-stabilized manner during locomotion, depending on the perceptual consequences of locomotion.     

Independent resources for attentional tracking in the left and right visual hemifields

The ability to divide attention enables people to keep track of up to four independently moving objects. We now show that this tracking capacity is independently constrained in the left and right visual fields as if separate tracking systems were engaged, one in each field. Specifically, twice as many targets can be successfully tracked when they are divided between the left and right hemifields as when they are all presented within the same hemifield. This finding places broad constraints on the anatomy and mechanisms of attentive tracking, ruling out a single attentional focus, even one that moves quickly from target to target.     

Comparing dogs and great apes in their ability to visually track object transpositions

Knowing that objects continue to exist after disappearing from sight and tracking invisible object displacements are two basic elements of spatial cognition. The current study compares dogs and apes in an invisible transposition task. Food was hidden under one of two cups in full view of the subject. After that both cups were displaced, systematically varying two main factors, whether cups were crossed during displacement and whether the cups were substituted by the other cup or instead cups were moved to new locations. While the apes were successful in all conditions, the dogs had a strong preference to approach the location where they last saw the reward, especially if this location remained filled. In addition, dogs seem to have especial difficulties to track the reward when both containers crossed their path during displacement. These results confirm the substantial difference that exists between great apes and dogs with regard to mental representation abilities required to track the invisible displacements of objects.     

Are things that are hard to physically move also hard to imagine moving?

Are objects that are more difficult to physically manipulate also more difficult to mentally manipulate? In our study, participants interacted with wooden objects modeled after the figures from Shepard and Metzler’s (1971) classic mental rotation experiment. One pair of objects was easy to physically rotate while another pair was difficult. They then completed a standard mental rotation task on images of these objects. Participants were slower to mentally rotate objects that were harder to physically rotate when they engaged in motor imagery. Further, this cost accrued with increasing angles of rotation. We verified this was the result of motor imagery by showing that the costs can be eliminated by using a strictly visual imagery strategy (imagining the objects moving on their own). These results reveal a striking constraint imposed by our real-world motor experiences on mental imagery, and also demonstrate a way that we can overcome such constraints.