Continuous Response Monitoring of Relative Time-to-Contact Judgments: Does Effective Information Change During an Approach Event?

In many previous studies of time-to-contact (TTC) judgments of approaching objects, a response was measured after observers viewed the entire event and was used to infer the informational basis for the judgment. Such measures primarily reflect the information used at the end of the approach event and may not reveal whether observers used different information at different times during the event. Evidence indicates that observers use multiple information sources and that the effectiveness of information varies with distance. We introduce a method in which observers continuously report which of 2 approaching objects would reach them first, throughout the approach. We identified the occurrence and time of response reversals. Most observers changed their relative TTC judgments during the event. The pattern of responses indicated that observers did not use tau early during the approach when objects were far and did not use optical size later when the objects were closer. Most observers relied on either optical size or optical expansion rate early during the approach and expansion rate later during the event, although there were individual differences. A single relative TTC judgment measured after observers view an approach event may not reflect judgments or their informational basis throughout the entire event.     

Effects of texture and shape on perceived time to passage: knowing "what" influences judging "when"

In the present study, we examined whether it is easier to judge when an object will pass one's head if the object's surface is textured. There are three reasons to suspect that this might be so: First, the additional (local) optic flow may help one judge the rate of expansion and the angular velocity more reliably. Second, local deformations related to the change in angle between the object and the observer could help track the object's position along its path. Third, more reliable judgments of the object's shape could help separate global expansioncaused by changes in distance from expansion due to changes in the angle between the object and the observer. We can distinguish among these three reasons by comparing performance for textured and uniform spheres and disks. Moving objects were displayed for 0.5-0.7 sec. Subjects had to decide whether the object would pass them before or after a beep that was presented 1 sec after the object started moving. Subjects were not more precise with textured objects. When the disk rotated in order to compensate for the orientation-related contraction that its image would otherwise undergo during its motion, it appeared to arrive later, despite the fact that this strategy increases the global rate of expansion. We argue that this is because the expected deformation of the object's image during its motion is considered when time to passage is judged. Therefore, the most important role for texture in everyday judgments of time to passage is probably that it helps one judge the object's shape and thereby estimate how its image will deform as it moves.     

Judgments of relative time-to-contact of more than two approaching objects: Toward a method

Observers reported which of as many as eight computer-generated approaching objects would “hit” them first. Accuracy was above chance probability except when two-object displays contained pictorial relative size information that contradicted relative time-to-contact (TTC) information. Mean d’ and response time was greater, but mean efficiency (Barlow, 1978) was smaller with eight objects than with two. Performance was less effective when global expansion contradicted TTC information than when local expansion contradicted TTC. Results suggest that observers can judge relative TTC with as many as eight objects when certain sources of information are consistent with TTC and that observers rely on information other than, or in conjunction with, optical TTC. Also, the sources of visual information that affect performance may vary with set size, and identification (but not detection) judgments may be constrained by limited-capacity processing.     

The effect of body posture on long-range time-to-contact estimation

On Earth, gravity accelerates freely moving objects downward, whereas upward-moving objects are being decelerated. Do humans take internalised knowledge of gravity into account when estimating time-to-contact (TTC, the time remaining before the moving object reaches the observer)? To answer this question, we created a motion-prediction task in which participants saw the initial part of an object's trajectory moving on a collision course prior to an occlusion. Observers had to judge when the object would make contact with them. The visual scene was presented with a head-mounted display. Participants lay either supine (looking up) or prone (looking down), suggestive of the ball either rising up or falling down toward them. Results showed that body posture had a significant effect on time-to-contact estimation, but only when occlusion times were long (2.5 s). The effect was also rather small. This lack of immediacy in the posture effect suggests that TTC estimation is initially robust toward the effect of gravity, which comes to bear only as more time is allowed for post-processing of the visual information.     

Visual impressions of penetration in the perception of objects in motion

Observers viewed visual stimuli in which one object moved to a position of partial occlusion by another. The objects were presented as two-dimensional profiles moving in an undefined space, so the partial occlusion supports several different physical interpretations. In fact some stimuli reliably gave rise to a perceptual impression that the moving object penetrated or pierced the stationary one. This kind of interaction impression has not previously been reported. The impression was maximized by rapid deceleration to a halt with minimal occlusion. If the object decelerated more slowly, so that it was completely occluded or projected from the far side of the stationary object, it was perceived as moving behind the stationary object. The shape of the moving object and its speed prior to occlusion had significant but small effects.     

Effect of distance instructions on size judgments

The proposition that in a reduced-cue setting subjects could use cognitive information about an object's distance to make accurate judgments of its size was tested. An improved paradigm was used to determine the effects of distance instructions per se. This paradigm also allowed independent tests of the effectiveness of cue reduction. The data indicated that cue reduction was successful and that the specific distance tendency governed size judgments when there were no distance instructions. When distance instructions were given, they produced size judgments in precisely the ratio predicted by the size-distance invariance hypothesis. However, there was a large constant error, which reflects a tendency of college students to overestimate the amount of distance signified by a verbal instruction. Hence, cognitive information in the form of verbal distance instructions has precise effects on size judgments, but the latter are not veridical, even in the absence of anchor effects from the specific distance tendency and residual perceptual cues.     

Time course of amodal completion revealed by a shape discrimination task

We measured the extent of amodal completion as a function of stimulus duration over the range of 15–210 msec, for both moving and stationary stimuli. Completion was assessed using a performancebased measure: a shape discrimination task that is easy if the stimulus is amodally completed and difficult if it is not. Specifically, participants judged whether an upright rectangle was longer horizontally or vertically, when the rectangle was unoccluded, occluded at its corners by four negative-contrast squares, or occluded at its corners by four zero-contrast squares. In the zero-contrast condition, amodal completion did not occur because there were no occlusion cues; in the unoccluded condition, the entire figure was present. Thus, comparing performance in the negative-contrast condition to these two extremes provided a quantitative measure of amodal completion. This measure revealed a rapid but measurable time course for amodal completion. Moving and stationary stimuli took the same amount of time to be completed (≈ 75 msec), but moving stimuli had slightly stronger completion at long durations.     

Estimating the relative weights of visual and auditory tau versus heuristic-based cues for time-to-contact judgments in realistic,familiar scenes by older and younger adults

Estimating time to contact (TTC) involves multiple sensory systems, including vision and audition. Previous findings suggested that the ratio of an object’s instantaneous optical size/sound intensity to its instantaneous rate of change in optical size/sound intensity (τ) drives TTC judgments. Other evidence has shown that heuristic-based cues are used, including final optical size or final sound pressure level. Most previous studies have used decontextualized and unfamiliar stimuli (e.g., geometric shapes on a blank background). Here we evaluated TTC estimates by using a traffic scene with an approaching vehicle to evaluate the weights of visual and auditory TTC cues under more realistic conditions. Younger (18–39 years) and older (65+ years) participants made TTC estimates in three sensory conditions: visual-only, auditory-only, and audio–visual. Stimuli were presented within an immersive virtual-reality environment, and cue weights were calculated for both visual cues (e.g., visual τ, final optical size) and auditory cues (e.g., auditory τ, final sound pressure level). The results demonstrated the use of visual τ as well as heuristic cues in the visual-only condition. TTC estimates in the auditory-only condition, however, were primarily based on an auditory heuristic cue (final sound pressure level), rather than on auditory τ. In the audio–visual condition, the visual cues dominated overall, with the highest weight being assigned to visual τ by younger adults, and a more equal weighting of visual τ and heuristic cues in older adults. Overall, better characterizing the effects of combined sensory inputs, stimulus characteristics, and age on the cues used to estimate TTC will provide important insights into how these factors may affect everyday behavior.     

碰撞时间估计的影响因素研究

本研究采用遮挡范式,考察了专职公交车驾驶员对不同类型、速度和方向运动物体的碰撞时间(TTC)估计.结果发现,被试对不同类别和速度运动物体的TTC估计有显著差异.这表明,除了视觉信息和物理信息之外,运动物体的概念信息也是影响横向运动TTC估计的重要因素.     

A Comparison of Time Estimations in Driving With Target-Only in Motion,Self-Only in Motion,and Self-and-Target in Motion

Using an occlusion paradigm, estimates of the time taken to reach a point with the target-only in motion (approaching vehicle judged by a stationary observer), self-only in motion (moving observer judgment of a stationary target), and both self-and-target in motion (moving observer judgment of an approaching vehicle), were contrasted. Judgments were made in built-up urban and textureless rural roadsides and on straight and curved roads. Thirty drivers with an average experience of 3.3 years drove a simulator and estimated when they should have passed vehicles that were occluded when the vehicles were 2.5 sec away. Target-only in motion estimates were more accurate (less underestimated) than self-only and self-and-target in motion estimates, which in turn were more accurate than self-only in motion judgments. The roadside manipulation only influenced estimates when participants were moving. Judgments were more accurate in the urban environment when other vehicles were stationary, but in the rural environment accuracy was greater when the other vehicles were approaching. Self-and-target in motion judgments were less accurate on curves than on straight roads. Possible theoretical explanations for the results are highlighted.     

Global and local contributions to the optical specification of time to contact: observer sensitivity to composite tau

First-order time remaining until a moving observer will pass an environmental element is optically specified in two different ways. The specification provided by global tau (based on the pattern of change of angular bearing) requires that the element is stationary and that the direction of motion is accurately detected, whereas the specification provided by composite tau (based on the patterns of change of optical size and optical distance) does not require either of these. We obtained converging evidence for our hypothesis that observers are sensitive to composite tau in four experiments involving relative judgments of time to passage with forced-choice methodology. Discrimination performance was enhanced in the presence of a local expansion component, while being unaffected when the detection of the direction of heading was impaired. Observers relied on the information carried in composite tau rather than on the information carried in its constituent components. Finally, performance was similar under conditions of observer motion and conditions of object motion. Because composite tau specifies first-order time remaining for a large number of situations, the different ways in which it may be detected are discussed.     

Time,change, and motion: The effects of stimulus movement on temporal perception

The effects of stimulus motion on time perception were examined in five experiments. Subjects judged the durations (6–18 sec) of a series of computer-generated visual displays comprised of varying numbers of simple geometrical forms. In Experiment 1, subjects reproduced the duration of displays consisting of stationary or moving (at 20 cm/sec) stimulus figures. In Experiment 2, subjects reproduced the durations of stimuli that were either stationary, moving slowly (at 10 cm/sec), or moving fast (at 30 cm/sec). In Experiment 3, subjects used the production method to generate specified durations for stationary, slow, and fast displays. In Experiments 4 and 5, subjects reproduced the duration of stimuli that moved at speeds ranging from 0 to 45 cm/sec. Each experiment showed that stimulus motion lengthened perceived time. In general, faster speeds lengthened perceived time to a greater degree than slower speeds. Varying the number of stimuli appearing in the displays had only limited effects on time judgments. Other findings indicated that shorter intervals tended to be overestimated and longer intervals underestimated (Vierordt’s law), an effect which applied to both stationary and moving stimuli. The results support a change model of perceived time, which maintains that intervals associated with more changes are perceived to be longer than intervals with fewer changes.     

Can semantic knowledge influence motion correspondence?

Semantic factors are presumed to have little influence on motion perception. Two experiments examined the effects of an object's semantic identity on motion correspondence using the Ternus paradigm. Motion correspondence was not influenced by whether the object depicted is typically moving or stationary, but it was influenced by the way(s) in which an object's components typically move relative to one another: perceived correspondence differed depending on whether the motion tokens constituted the feet of a person walking or the wheels of a car. Apparently, semantic knowledge can influence motion correspondence, although such influence is weak and may be restricted to certain types of semantic information. The adaptive significance of such restricted influences is considered.     

遮挡范式下运动速度和方向对碰撞时间估计绩效指标的影响

为探索运动速度和方向对碰撞时间（TTC）估计的影响,采用3运动速度×4运动方向的双因素设计开展了实验研究。结果发现,在相对慢速条件下,受试者TTC估计的准确性显著差于相对中速和相对快速条件;仅在相对慢速条件下受试者对竖直方向的TTC估计准确度显著差于水平方向、低估TTC的比例显著高于高估TTC的比例。结果表明,运动速度对TTC估计绩效指标的影响相对较强,运动方向对其影响相对较弱;两个因素的影响存在交互作用。     

The role of instructions and familiar size in absolute judgments of size and distance.

The effects of familiar size and instructions (apparent, objective) on direct reports of size and distance were evaluated. Subjects estimated the size and distance of two different-sized playing cards or two unfamiliar stimuli under either apparent or objective instructions. The stimuli were presented successively at a distance of 5.48 m under reduced-cue conditions. The form of the instructions selectively influenced the effect of familiar size on absolute judgments of size and distance, with apparent instructions minimizing, and objective instructions promoting, familiar-size effects. The ratio of the distance judgments of the first to the second presented stimuli approximated the relative retinal sizes of the two objects under both apparent and objective instructions, while the ratio of size judgments tended to be either influenced by or independent of the object's relative retinal sizes under apparent and objective instructions, respectively. These results are consistent with Gogel's theory of off-size perception and, in particular, with the claim that, in comparison with apparent instructions, objective instructions are more likely to direct observers to base their judgments on cognitive, as opposed to perceptual, sources of spatial information.     

Dynamic Spatial Ability and Psychomotor Performance

Dynamic spatial ability is one's ability to estimate when a moving object will reach a destination, or one's skill in making time-to-contact (TTC) judgments. In 2 studies, we investigated the nature of dynamic spatial ability and its role in psychomotor (PM) task performance. In the first study, 405 basic military trainees were given both spatial and nonspatial versions of TTC and comparative arrival-time tasks, and we found that the spatial and nonspatial versions of the tasks were more highly correlated than the spatial tasks were to each other, suggesting that a timing, rather than a spatial, mechanism underlies performance of dynamic spatial tasks. In the second study with 376 military trainees, we found that performance on a set of PM tasks was predicted by a general working-memory (WM) Capacity factor (r = .45) and an orthogonal Temporal Processing (TP) factor (r = .55), suggesting the importance of the dynamic spatial, or of the TP factor, in many real-world activities.     

Object updating and the flash-lag effect

Flash lag is a misperception of spatial relations between a moving object and a briefly flashed stationary one. This study began with the observation that the illusion occurs when the moving object continues following the flash, but is eliminated if the object's motion path ends with the flash. The data show that disrupting the continuity of the moving object, via a transient change in size or color, also eliminates the illusion. We propose that this is because a large feature change leads to the formation of a second object representation. Direct evidence for this proposal is provided by the results for a corollary perceptual feature of the disruption in object continuity: the perception of two objects, rather than only one, on the motion path.     

Judging the contact-times of multiple objects: Evidence for asymmetric interference

The accuracy of time-to-contact (TTC) judgments for single approaching objects is well researched, however, close to nothing is known about our ability to make simultaneous TTC judgments for two or more objects. Such complex judgments are required in many everyday situations, for instance when crossing a multi-lane street or when engaged in multi-player ball games. We used a prediction-motion paradigm in which participants simultaneously estimated the absolute TTC of two objects, and compared the performance to a standard single-object condition. Results showed that the order of arrival of the two objects determined the accuracy of the TTC estimates: Estimation of the first-arriving object was unaffected by the added complexity compared to the one-object condition, whereas the TTC of the second-arriving object was systematically overestimated. This result has broad implications for complex everyday situations. We suggest that it is akin to effects observed in experiments on the psychological refractory period (PRP) and that the proactive interference of the first-arriving object indicates a bottleneck or capacity sharing at the central stage.     

Object and observer motion in the perception of objects by infants

Sixteen-week-old human infants distinguish optical displacements given by their own motion from displacements given by moving objects, and they use only the latter to perceive the unity of partly occluded objects. Optical changes produced by moving the observer around a stationary object produced attentional levels characteristic of stationary observers viewing stationary displays and much lower than those shown by stationary observers viewing moving displays. Real displacements of an object with no subject-relative displacement, produced by moving an object so as to maintain a constant relation to the moving observer, evoked attentional levels that were higher than with stationary displays and more characteristic of attention to moving displays, a finding suggesting detection of the real motion. Previously reported abilities of infants to perceive the unity of partly occluded objects from motion information were found to depend on real object motion rather than on optical displacements in general. The results suggest that object perception depends on registration of the motions of surfaces in the three-dimensional layout.     

Differential effects of shared attention on perception of heading and 3-D object motion

When a person moves in a straight line through a stationary environment, the images of object surfaces move in a radial pattern away from a single point. This point, known as the focus of expansion (FOE), corresponds to the person's direction of motion. People judge their heading from image motion quite well in this situation. They perform most accurately when they can see the region around the FOE, which contains the most useful information for this task. Furthermore, a large moving object in the scene has no effect on observer heading judgments unless it obscures the FOE. Therefore, observers may obtain the most accurate heading judgments by focusing their attention on the region around the FOE. However, in many situations (e.g., driving), the observer must pay attention to other moving objects in the scene (e.g., cars and pedestrians) to avoid collisions. These objects may be located far from the FOE in the visual field. We tested whether people can accurately judge their heading and the three-dimensional (3-D) motion of objects while paying attention to one or the other task. The results show that differential allocation of attention affects people's ability to judge 3-D object motion much more than it affects their ability to judge heading. This suggests that heading judgments are computed globally, whereas judgments about object motion may require more focused attention.