Tracking unique objects

Is content addressable in the representation that subserves performance in multiple-object-tracking (MOT) experiments? We devised an MOT variant that featured unique, nameable objects (cartoon animals) as stimuli. There were two possible response modes: standard, in which observers were asked to report the locations of all target items, and specific, in which observers had to report the location of a particular object (e.g., “Where is the zebra?”). A measure of capacity derived from accuracy allowed for comparisons of the results between conditions. We found that capacity in the specific condition (1.4 to 2.6 items across several experiments) was always reliably lower than capacity in the standard condition (2.3 to 3.4 items). Observers could locate specific objects, indicating a content-addressable representation. However, capacity differences between conditions, as well as differing responses to the experimental manipulations, suggest that there may be two separate systems involved in tracking, one carrying only positional information, and one carrying identity information as well.     

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.     

Is color an intrinsic property of object representation?

The role of color in object representation was examined by using a variation of the Stroop paradigm in which observers named the displayed colors of objects or words. In experiment 1, colors of color-diagnostic objects were manipulated to be either typical or atypical of the object (eg a yellow banana versus a purple banana). A Stroop-like effect was obtained, with faster color-naming times for the typical as compared to the atypical condition. In experiment 2, naming colors on words specifying these same color-diagnostic objects reversed this pattern, with the typical condition producing longer response times than the atypical condition. In experiment 3, a blocked condition design that used the same words and colors as experiment 2 produced the standard Stroop-like facilitation for the typical condition. These results indicate that color is an intrinsic property of an object's representation at multiple levels. In experiment 4, we examined the specific level(s) at which color-shape associations arise by following the tasks used in experiments 1 and 2 with a lexical-decision task in which some items were conceptually related to items shown during color naming (eg banana/monkey). Priming for these associates was observed following color naming of words, but not pictures, providing further evidence that the color-shape associations responsible for the differing effects obtained in experiments 1 and 2 are due to the automatic activation of color-shape associations at different levels of representation.     

Multiple object juggling: Changing what is tracked during extended multiple object tracking

The multiple object tracking (MOT) task has been a useful tool for studying the deployment of limited-capacity visual resources over time. Since it involves sustained attention to multiple objects, this task is a promising model for real-world visual cognition. However, real-world tasks differ in two critical ways from standard laboratory MOT designs. First, in real-world tracking, it is unusual for the set of tracked items to be identified all at once and to remain unchanged over time. Second, real-world tracking tasks may need to be sustained over a period of minutes, and not mere seconds. How well is MOT performance maintained over extended periods of time? In four experiments, we demonstrate that observers can dynamically “juggle” objects in and out of the tracked set with little apparent cost, and can sustain this performance for up to 10 min at a time. This performance requires implicit or explicit feedback. In the absence of feedback, performance tracking drops steadily over the course of several minutes.     

不同目标标记方式对多目标追踪表现的影响

有关多目标追踪的研究多采用目标闪烁数次或目标周围出现方框等视觉方式对目标进行标记。在已有研究基础上,通过2个实验比较了不同目标数量下视觉平行标记、视觉序列标记、听觉序列标记(视听跨通道标记)和视听双通道序列标记4种目标标记方式对多目标追踪表现的影响。研究结果表明在多目标追踪任务中,线索阶段目标的视觉标记比视听跨通道标记更有效,且不受目标的序列标记或平行标记的影响,而视觉和听觉编码结合（视听双通道标记）可以促进任务难度较高时的追踪表现。     

Working memory for relations among objects

Across many areas of study in cognition, the capacity of working memory (WM) is widely agreed to be roughly three to five items: three to five objects (i.e., bound collections of object features) in the literature on visual WM or three to five role bindings (i.e., objects in specific relational roles) in the literature on memory and reasoning. Three experiments investigated the capacity of observers’ WM for the spatial relations among objects in a visual display, and the results suggest that the “items” in WM are neither simply objects nor simply role bindings. The results of Experiment 1 are most consistent with a model that treats an “item” in visual WM as an object, along with the roles of all its relations to one other object. Experiment 2 compared observers’ WM for object size with their memory for relative size and provided evidence that observers compute and store objects’ relations per se (rather than just absolute size) in WM. Experiment 3 tested and confirmed several more nuanced predictions of the model supported by Experiment 1. Together, these findings suggest that objects are stored in visual WM in pairs (along with all the relations between the objects in a pair) and that, from the perspective of WM, a given object in one pair is not the same “item” as that same object in a different pair.     

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.     

Why don't we see changes?: The role of attentional bottlenecks and limited visual memory

Seven experiments explore the role of bottlenecks in selective attention and access to visual short-term memory in the failure of observers to identify clearly visible changes in otherwise stable visual displays. Experiment One shows that observers fail to register a color change in an object even if they are cued to the location of the object by a transient at that location as the change is occurring. Experiment Two shows the same for orientation change. In Experiments Three and Four, attention is directed to specific objects prior to making changes in those objects. Observers have only a very limited memory for the status of recently attended items. Experiment Five reveals that observers have no ability to detect changes that happen after attention has been directed to an object and before attention returns to that object. In Experiment Six, attention is cued at rates that more closely resemble natural rates and Experiment Seven uses natural images. Memory capacity remains very small (<4 items).     

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.     

Simultaneous control of attention by multiple working memory representations

Working memory representations play a key role in controlling attention by making it possible to shift attention to task-relevant objects. Visual working memory has a capacity of three to four objects, but recent studies suggest that only one representation can guide attention at a given moment. We directly tested this proposal by monitoring eye movements while observers performed a visual search task in which they attempted to limit attention to objects drawn in two colors. When the observers were motivated to attend to one color at a time, they searched many consecutive items of one color (long run lengths) and exhibited a delay prior to switching gaze from one color to the other (switch cost). In contrast, when they were motivated to attend to both colors simultaneously, observers' gaze switched back and forth between the two colors frequently (short run lengths), with no switch cost. Thus, multiple working memory representations can concurrently guide attention.     

Direction information in multiple object tracking is limited by a graded resource

Is multiple object tracking (MOT) limited by a fixed set of structures (slots), a limited but divisible resource, or both? Here, we answer this question by measuring the precision of the direction representation for tracked targets. The signature of a limited resource is a decrease in precision as the square root of the tracking load. The signature of fixed slots is a fixed precision. Hybrid models predict a rapid decrease to asymptotic precision. In two experiments, observers tracked moving disks and reported target motion direction by adjusting a probe arrow. We derived the precision of representation of correctly tracked targets using a mixture distribution analysis. Precision declined with target load according to the square-root law up to six targets. This finding is inconsistent with both pure and hybrid slot models. Instead, directional information in MOT appears to be limited by a continuously divisible resource.     

Eye movements and scene perception: memory for things observed

In this study, we examined the characteristics of on-line scene representations, using a partial-report procedure. Subjects inspected a simple scene containing seven objects for 1, 3, 5, 9, or 15 fixations; shortly after scene offset, a marker cued one scene location for report. Consistent with previous research, the results indicated that scene representations are relatively sparse; even after 15 fixations on a scene, the subjects remembered the position/identity pairings for only about 78% of the objects in the scene, or the equivalent of about five objects-worth of information. Report of the last three objects that were foveated and of the object about to be foveated was very accurate, however, suggesting that recently attended information in a scene is represented quite well. Information about the scene appeared to accumulate over multiple fixations, but the capacity of the on-line scene representation appeared to be limited to about five items. Implications for recent theories of scene representation are discussed.     

Wheatstone—Panum limiting case: Occlusion, camouflage, and vergence-induced disparity cues

We examined effects of binocular occlusion, binocular camouflage, and vergence-induced disparity cues on the perceived depth between two objects when two stimuli are presented to one eye and a single stimulus to the other (Wheatstone—Panum limiting case). The perceived order and magnitude of the depth were examined in two experimental conditions: (1) The stimulus was presented on the temporal side (occlusion condition) and (2) the nasal side (camouflage condition) of the stimulus pair on one retina so as to fuse with the single stimulus on the other retina. In both conditions, the separation between the stimulus pair presented to one eye was systematically varied. Experiment 1, with 16 observers, showed that the fused object was seen in front of the nonfused object in the occlusion condition and was seen at the same distance as the nonfused object in the camouflage condition. The perceived depth between the two objects was constant and did not depend on the separation of the stimulus pair presented to one eye. Experiment 2, with 45 observers, showed that the disparity induced by vergence mainly determined the perceived depth, and the depth magnitude increased as the separation of the stimulus pair was made wider. The results suggest that (1) occlusion provides depth-order information but not depth-magnitude information, (2) camouflage provides neither depth-order nor depth-magnitude information, and (3) vergence-induced disparity provides both order and magnitude information.     

Wheatstone-Panum limiting case: occlusion, camouflage, and vergence-induced disparity cues.

We examined effects of binocular occlusion, binocular camouflage, and vergence-induced disparity cues on the perceived depth between two objects when two stimuli are presented to one eye and a single stimulus to the other (Wheatstone-Panum limiting case). The perceived order and magnitude of the depth were examined in two experimental conditions: (1) The stimulus was presented on the temporal side (occlusion condition) and (2) the nasal side (camouflage condition) of the stimulus pair on one retina so as to fuse with the single stimulus on the other retina. In both conditions, the separation between the stimulus pair presented to one eye was systematically varied. Experiment 1, with 16 observers, showed that the fused object was seen in front of the nonfused object in the occlusion condition and was seen at the same distance as the nonfused object in the camouflage condition. The perceived depth between the two objects was constant and did not depend on the separation of the stimulus pair presented to one eye. Experiment 2, with 45 observers, showed that the disparity induced by vergence mainly determined the perceived depth, and the depth magnitude increased as the separation of the stimulus pair was made wider. The results suggest that (1) occlusion provides depth-order information but not depth-magnitude information, (2) camouflage provides neither depth-order nor depth-magnitude information, and (3) vergence-induced disparity provides both order and magnitude information.     

知觉表征精度对工作记忆中抑制干扰能力的影响

工作记忆的容量十分有限,需要选择性地抑制与目标无关信息的干扰,工作记忆容量高的个体,其抑制干扰的能力也更强。本研究采用带有不同形状干扰刺激的色块颜色回忆任务考察干扰对工作记忆容量和表征精度的影响,结果发现,当负荷超出工作记忆容量范围时,干扰减少了记忆所能表征客体的个数;当负荷在工作记忆容量范围内时,干扰降低了记忆中表征客体的精度。更进一步,研究采用独立的知觉任务来测量知觉表征的精度,并探讨作为信息加工的初始阶段的知觉表征如何影响工作记忆加工过程中抑制干扰的能力。将实验中收集的48名有效被试按照知觉表征精度的高低平均分为两组,结果发现上述干扰效应主要表现在知觉表征精度较低的组中,并且该组中知觉表征精度越高的个体,其工作记忆抑制干扰的能力也越强。本研究为实践中通过知觉训练来提升工作记忆的抑制干扰能力提供了理论指导。     

Structural similarity and spatiotemporal noise effects on learning dynamic novel objects

The spatiotemporal pattern projected by a moving object is specific to that object, as it depends on both the shape and the dynamics of the object. Previous research has shown that observers learn to make use of this spatiotemporal signature to recognize dynamic faces and objects. In two experiments, we assessed the extent to which the structural similarity of the objects and the presence of spatiotemporal noise affect how these signatures are learned and subsequently used in recognition. Observers first learned to identify novel, structurally distinctive or structurally similar objects that rotated with a particular motion. At test, each learned object moved with its studied motion or with a non-studied motion. In the non-studied motion condition we manipulated either dynamic information alone (experiment 1) or both static and dynamic information (experiment 2). Across both experiments we found that changing the learned motion of an object impaired recognition performance when 3-D shape was similar or when the visual input was noisy during learning. These results are consistent with the hypothesis that observers use learned spatiotemporal signatures and that such information becomes progressively more important as shape information becomes less reliable.     

How do we track invisible objects?

We previously demonstrated that observers in multiple object tracking experiments can successfully track targets when all the objects simultaneously vanish for periods lasting several hundred milliseconds (Alvarez, Horowitz, Arsenio, Dimase, &; Wolfe, 2005). How do observers do this? Since observers can track objects that move behind occluders (e.g., Scholl &; Pylyshyn, 1999), they may treat a temporal gap as a case of complete occlusion. If so, performance should improve if occlusion cues (deletion and accretion) are provided and items disappear and reappear one by one (asynchronously), rather than simultaneously. However, we found better performance with simultaneous than with asynchronous disappearance (Experiment 1), whereas occlusion cues were detrimental (Experiment 2). We propose that observers tolerate a gap in tracking by storing the current task state when objects vanish and resuming tracking on the basis of that memory when the objects reappear (a task-switching account).     

Category-based grouping in working memory and multiple object tracking

Two prominent cognitive capacity limitations are the maximal number of objects we can place in working memory (WM) and the maximal number of objects we can track in a display. Both are believed to have a numeric value of 3 or 4, which has led to the proposal that we have a general cognitive capacity, and that this capacity is most likely linked to limitations of how many objects we can attend simultaneously. Based on previous results showing that we can memorize more objects if they come from different categories than if they come from the same category (e.g., Feigenson & Halberda, 2008; Wong, Peterson, & Thompson, 2008; Wood, 2008), we compare how category-based grouping affects performance for WM and multiple object tracking (MOT). We present participants with either “pure” displays of either cars or faces, or with “mixed” displays of cars and faces. Overall, the effects of category are weak. In some analyses but not others, we replicate the mixed advantage for WM, albeit with a small effect size. In contrast, we observe a weak pure advantage for MOT tasks, at least in a meta-analysis of five experiments, but not in all experiments. Accordingly, WM and MOT tasks differed significantly in their sensitivity to category membership. We also find that WM is slightly better for faces than for cars, but that no such difference exists for MOT. We tentatively suggest that cognitive capacity limitations in different domains are at least partially due to the limitations of distinct mechanisms.     

视觉工作记忆的同类别存储优势

概念规律如记忆项间的类别关系如何影响视觉工作记忆容量是一个有争议的问题。针对该问题, 学界存在两种预测截然不同的假说：(1)混合类别优势假说, (2)同类别优势假说。综述文献发现, 该类研究均采用带有细节特征的真实客体作为实验材料, 因此前人研究中发现的混合类别优势效应或同类别优势效应中必然混有低水平知觉特征的影响。故本研究采用去除细节信息的动物剪影作为记忆材料来排除上述因素的影响, 旨在厘清上述两种假设, 并采用对侧延迟活动作为神经指标, 来进一步探讨概念规律影响工作记忆容量的内在机制。两个行为实验发现, 不论记忆项同时呈现还是序列呈现, 均存在同类别记忆优势效应。脑电实验结果发现相比记忆不同类别客体, 记忆同等数量的同类别客体诱发的对侧延迟活动的幅值更小。上述结果一致表明, 视觉工作记忆可借助概念的方式将同类别客体加以组织, 从而有效扩大视觉工作记忆容量, 支持了同类别优势假说。     

Active and passive scene recognition across views.

Recent evidence suggests that scene recognition across views is impaired when an array of objects rotates relative to a stationary observer, but not when the observer moves relative to a stationary display [Simons, D.J., Wang, R.F., 1998. Perceiving real-world viewpoint changes. Psychological Science 9, 315-320]. The experiments in this report examine whether the relatively poorer performance by stationary observers across view changes results from a lack of perceptual information for the rotation or from the lack of active control of the perspective change, both of which are present for viewpoint changes. Three experiments compared performance when observers passively experienced the view change and when they actively caused the change. Even with visual information and active control over the display rotation, change detection performance was still worse for orientation changes than for viewpoint changes. These findings suggest that observers can update a viewer-centered representation of a scene when they move to a different viewing position, but such updating does not occur during display rotations even with visual and motor information for the magnitude of the change. This experimental approach, using arrays of real objects rather than computer displays of isolated individual objects, can shed light on mechanisms that allow accurate recognition despite changes in the observer's position and orientation.