Does Binocular Disparity or Familiar Size Information Override Effects of Relative Size on Judgements of Time to Contact?

Does the Size-Arrival Effect Occur With an Active Collision-Avoidance Task in an Immersive 3D Virtual Reality Environment?

OBJECTIVE

Determine whether the size-arrival effect (SAE) occurs with immersive, 3D visual experiences and active collision-avoidance responses.

BACKGROUND

When a small near object and a large far object approach the observer at the same speeds, the large object appears to arrive before the small object, known as the size-arrival effect (SAE), which may contribute to crashes between motorcycles and cars. Prior studies of the SAE were limited because they used two dimensional displays and asked participants to make passive judgments.

METHOD

Participants viewed approaching objects using a virtual reality (VR) headset. In an active task, participants ducked before the object hit them. In a passive prediction-motion (PM) judgment, the approaching object disappeared, and participants pressed a button when they thought the object would hit them. In a passive relative TTC judgment, participants reported which of two approaching objects would reach them first.

RESULTS

The SAE occurred with the PM and relative TTC tasks but not with the ducking task. The SAE can occur in immersive 3D environments but is limited by the nature of the task and display.

APPLICATION

Certain traffic situations may be more prone to the SAE and have higher risk for collisions. For example, in left-turn scenarios (e.g., see Levulis, 2018), drivers make passive judgments when oncoming vehicles are far and optical expansion is slow, and binocular disparity putatively is ineffective. Collision-avoidance warning systems may be needed more in such scenarios than when vehicles are near and drivers' judgments of TTC may be more accurate (DeLucia, 2008).

Semantic modulation of time-to-collision judgments

Observers are able to make generally accurate judgments of the time-to-collision (TTC) of approaching stimuli. Traditional theories have emphasized the role of optical cues about the expansion of the retinal image in this ability. Recent work, however, has further emphasized the role of semantic information about the object. Here we investigate the role of semantic information in TTC judgments by presenting a range of real-world objects, which varied widely in size, weight, and hardness. Our results show that the physical characteristics of looming stimuli predict observers' TTC estimations. Bigger, heavier, and harder objects were underestimated more, relative to smaller, lighter, and softer objects. As expected, actual TTC and stimulus size were also significant predictors of TTC judgments. In estimating the arrival time of looming stimuli, observers automatically take into account several characteristics of the stimuli, even though these characteristics are completely task irrelevant. This suggests that semantic properties of seen objects and the consequences of their impact on the observer's body are processed automatically.

Examining the Role of Familiarity in the Perception of Depth

Bishop Berkeley suggested that the distance of an object can be estimated if the object’s size is familiar to the observer. It has been suggested that humans can perceive the distance of the object by using such “familiarity” information, but most or many of the prior experiments that found an effect of familiarity were not designed to minimize or eliminate potential influences of: higher cognitive factors on the observers’ responses, or the influences of low-level image features in the visual stimuli used. We looked for the familiarity effect in two experiments conducted both in Russia and Japan. The visual stimuli used were images of three coins used in Russia and Japan. The participants’ depth perception was measured with a multiple-choice task testing the perceived depth-order of the coins. Our expectation was that any effect of “familiarity” on depth perception would only be observed with the coins of the participant’s country. We expected a substantial familiarity effect based on our meta-analysis of the “familiarity” effects observed in prior experiments. But, our results in both experiments showed that the familiarity effect was virtually zero. These findings suggest that the importance of a familiarity effect in depth perception should be reconsidered.

Impending Collision Judgment from an Egocentric Perspective in Real and Virtual Environments: A Review

The human egocentric perception of approaching objects and the related perceptual processes have been of interest to researchers for several decades. This article gives a literature review on numerous studies that investigated the phenomenon when an object approaches an observer (or the other way around) with the goal to single out factors that influence the perceptual process. A taxonomy of metrics is followed by a breakdown of different experimental measurement methods. Thereinafter, potential factors affecting the judgment of approaching objects are compiled and debated while divided into human factors (e.g., gender, age, and driving experience), compositional factors (e.g., approaching velocity, spatial distance, and observation time), and technical factors (e.g., field of view, stereoscopy, and display contrast). Experimental findings are collated, juxtaposed, and critically discussed. With virtual-reality devices having taken a tremendous developmental leap forward in the past few years, they have been able to gain ground in experimental research. Therefore, special attention in this article is also given to the perception of approaching objects in virtual environments and put in contrast to the perception in reality.

Availability of attention affects time-to-contact estimation

To estimate the time-to-contact (TTC) of a moving object, numerous studies have focused on the type of information or gaze strategy used by the observer. However, it remains to be determined whether and how attention could affect TTC estimation. In particular, how does TTC estimation operate when less attention is available? To answer this question, we conducted two experiments in which the participants had to perform an absolute (Experiment 1) or relative (Experiment 2) prediction-motion task, either alone (i.e., in single-task condition) or along with a secondary, visual working-memory task (i.e., in dual-task condition). In both experiments, we found that TTC estimation was superior in dual-task condition relative to single-task condition. This finding suggests that the reduction of available attention actually improves TTC estimation. We discuss possible explanations as well as theoretical implications for this seemingly counter-intuitive finding. Further research is needed to investigate if (in)attention facilitates or only shifts TTC estimation.

Perception of time to contact of slow- and fast-moving objects using monocular and binocular motion information

The role of the monocular-flow-based optical variable τ in the perception of the time to contact of approaching objects has been well-studied. There are additional contributions from binocular sources of information, such as changes in disparity over time (CDOT), but these are less understood. We conducted an experiment to determine whether an object's velocity affects which source is most effective for perceiving time to contact. We presented participants with stimuli that simulated two approaching squares. During approach the squares disappeared, and participants indicated which square would have contacted them first. Approach was specified by (a) only disparity-based information, (b) only monocular flow, or (c) all sources of information in normal viewing conditions. As expected, participants were more accurate at judging fast objects when only monocular flow was available than when only CDOT was. In contrast, participants were more accurate judging slow objects with only CDOT than with only monocular flow. For both ranges of velocity, the condition with both information sources yielded performance equivalent to the better of the single-source conditions. These results show that different sources of motion information are used to perceive time to contact and play different roles in allowing for stable perception across a variety of conditions.

Gibson and Crooks (1938): Vision and Validation

Gibson and Crooks (1938) is a landmark article that was ahead of its time, has had sustained and significant impact, and raised issues that are still being considered now. Although most influential in driving research, the concepts Gibson and Crooks presented influenced other domains, including surgery and naval operations. After summarizing the key concepts in Gibson and Crooks, we show how those concepts foreshadowed key principles of Gibson’s ecological approach to visual perception (Gibson, 1979/1986). We then describe research that validates and builds on the analyses of Gibson and Crooks. We conclude that Gibson and Crooks will continue to have impact and generate research for years to come.

Integration of Action and Size Perception Through Practice

Size perception is known to influence our usual interactions with environment. Numerous studies highlighted that during the visual presentation of an object, the properties of manual actions vary as a function of this object's size. In order to better understand the dynamic variations of relationships between size perception and action, we used an experimental paradigm consisting in two phases. During a previous implicit learning phase, a manual response (right or left) was specifically associated with the appearance of a large or small stimulus. During further test phase, participants were required to prepare a response while discriminating the color of a stimulus (GO/No GO task). We observed that the response execution was faster when the size of the stimulus was congruent with the size that had been associated to this response (during implicit learning phase). These results suggest that when a response usually co-occurs with visual stimuli characterized by a specific size pattern, the response and the size pattern become integrated. Any subsequent preparation and execution of this action are therefore influenced by the reactivation of this visual pattern. This result brings out new insights on how sensorimotor interactions may modulate the ability to anticipate perceptive size variations in the environment.

Effects of oncoming vehicle size on overtaking judgments

During overtaking maneuvers on two-way highways drivers must temporarily cross into the opposite lane of traffic, and may face oncoming vehicles. To judge when it is safe to overtake, drivers must estimate the time-to-contact (TTC) of the oncoming vehicle. Information about an oncoming vehicle's TTC is available in the optical expansion pattern, but it is below threshold during high-speed overtaking maneuvers, which require a large passing distance. Consequently, we hypothesized that drivers would rely on perceived distance and velocity, and that their overtaking judgments would be influenced by oncoming vehicle size. A driving simulator was used to examine whether overtaking judgments are influenced by the size of an oncoming vehicle, and by whether a driver actively conducts the overtaking maneuver or passively judges whether it is safe to overtake. Oncoming motorcycles resulted in more accepted gaps and false alarms than larger cars or trucks. Results were due to vehicle size independently of vehicle type, and reflected shifts in response bias rather than sensitivity. Drivers may misjudge the distances of motorcycles due to their relatively small sizes, contributing to accidents due to right-of-way violations. Results have implications for traffic safety and the potential role of driver-assistance technologies.

The time course of estimating time-to-contact: switching between sources of information

The different sources of information that can be used to estimate time-to-contact may have different degrees of reliability across time. For example, after a given presentation or display time, an absolute change of angular size can be more reliable than the corresponding estimation of the rate of angular expansion (e.g. motion information). One could then expect systematic biases in the observer's responses for different times of stimulus exposure. In one experiment, observers judged whether approaching objects arrived at the point of observation before or after a reference beep (1.2s) under monocular, and binocular plus monocular vision. Five display times from 0.1 to 0.9s were used. Unlike monocular viewing, where accuracy increased monotonically with display time, an interesting non-linearity occurred for objects with small size when binocular information was available. Accuracy reached maximum values for small objects with only 0.3s of vision with stereopsis. This accuracy, however, dropped significantly after 0.4s of exposure and increased again linearly with time. This is consistent with subjects switching from using binocular information to using monocular motion information when it started to become more reliable. We also explored whether monocular cues were combined differently across time by fitting a model that relates visual angle to its rate of expansion. Results show that subjects relied more on angular motion information (i.e. rate of expansion) with presentation time but interrupting this motion integration process led to a loss of accuracy in time-to-contact judgments.

Effects of Size on Collision Perception and Implications for Perceptual Theory and Transportation Safety

People avoid collisions when they walk or drive, and they create collisions when they hit balls or tackle opponents. To do so, people rely on the perception of depth (perception of objects’ locations) and time-to-collision (perception of when a collision will occur), which are supported by different information sources. Depth cues, such as relative size, provide heuristics for relative depth, whereas optical invariants, such as tau, provide reliable time-to-collision information. One would expect people to rely on invariants rather than depth cues, but the size-arrival effect shows the contrary: People reported that a large far approaching object would hit them sooner than a small near object that would have hit first. This effect of size on collision perception violates theories of time-to-collision perception based solely on the invariant tau and suggests that perception is based on multiple information sources, including heuristics. The size-arrival effect potentially can lead drivers to misjudge when a vehicle would arrive at an intersection and is considered a contributing factor in motorcycle accidents. In this article, I review research on the size-arrival effect and its theoretical and practical implications.

Threatening pictures induce shortened time-to-contact estimates

The ability to estimate the time remaining until collision occurs with an approaching object (time-to-collision, TTC) is crucial for any mobile animal. In the present study, we report three experiments examining whether higher level cognitive factors, represented by affective value of approaching objects, could affect judgments of TTC. A theory of TTC estimates based purely on the optical variable tau does not predict an influence of the affective value of an approaching object. In Experiments 1 and 2, we compared TTC estimates of threatening and neutral pictures that approached our participants on a screen and disappeared from view before a collision would have occurred. Images were taken from the International Affective Picture System. Threatening pictures-in particular, the picture of a frontal attack-were judged to collide earlier than neutral pictures. In Experiment 3, the approaching stimuli were faces with different emotional expressions. TTC tended to be underestimated for angry faces. We discuss these results, considering the roles of affective and cognitive mechanisms modulating TTC estimation and general time perception.

Evaluating methods to measure time-to-contact

Many every-day activities necessitate an estimate of the time remaining until an object will hit us: the time-to-contact (TTC). Observers' skill in estimating TTC has been studied by considering the use and combination of key visual signals (e.g. looming and disparity). However, establishing observers' proficiency in estimating TTC can be complicated, as the variable of interest (time) is typically highly correlated with other signals (e.g. target velocity or displacement). As a result, observers' responses may be based on correlates of TTC rather than on TTC itself. Here we evaluate two widely-used TTC tasks: one absolute task in which observers pressed a button to indicate the estimated TTC, and a relative task in which TTC was judged relative to a reference. We test how a wide range of experimental variables that co-vary with TTC contribute to observers' judgments. We systematically vary the correlation between TTC and its covariates and test how psychophysical judgments are affected. We show that for both absolute and relative estimation tasks, observers' responses are best explained on the basis that they judge TTC rather than one (or more) of its covariates. Our results suggest that relative tasks are preferable when assessing TTC, and we suggest a number of analyses methods to ensure that participants' judgements correspond to the variable under investigation.

The effects of familiar size and object trajectories on time-to-contact judgements

Many interceptive actions involve interactions with objects that are familiar to the observer and have known sizes. Two experiments investigated how known size influences observers' perception of time-to-contact (T(c)). Participants made T(c) judgements of objects that were either ambiguously sized, standard-size in identity/familiarity, or off-size in identity/familiarity, and simulated as approaching on linear trajectories (Experiment 1), or linear versus parabolic trajectories (Experiment 2). In Experiment 1, T(c) judgements were influenced by the size of the object in the three object identity/familiarity conditions; the greatest size effect occurred in the off-size condition compared to the ambiguous size and standard-size conditions. The results of Experiment 2 replicated these results and found that size effects were not reduced with displays simulating parabolic trajectories, that is, displays simulating ecologically valid free-falling objects. Taken together, the finding that T(c) judgements are influenced by object identity/familiarity does not provide support for the tau hypothesis, nor the hypothesis that T(c) judgements are based solely on optic expansion rates. However, the results do provide support for the proposition that T(c) judgements are based on a combination of rate of retinal image expansion and object identity/familiarity information, the latter information requiring observers to have prior experience with, or knowledge about, the objects.

Extrapolation of vertical target motion through a brief visual occlusion

It is known that arbitrary target accelerations along the horizontal generally are extrapolated much less accurately than target speed through a visual occlusion. The extent to which vertical accelerations can be extrapolated through an occlusion is much less understood. Here, we presented a virtual target rapidly descending on a blank screen with different motion laws. The target accelerated under gravity (1g), decelerated under reversed gravity (-1g), or moved at constant speed (0g). Probability of each type of acceleration differed across experiments: one acceleration at a time, or two to three different accelerations randomly intermingled could be presented. After a given viewing period, the target disappeared for a brief, variable period until arrival (occluded trials) or it remained visible throughout (visible trials). Subjects were asked to press a button when the target arrived at destination. We found that, in visible trials, the average performance with 1g targets could be better or worse than that with 0g targets depending on the acceleration probability, and both were always superior to the performance with -1g targets. By contrast, the average performance with 1g targets was always superior to that with 0g and -1g targets in occluded trials. Moreover, the response times of 1g trials tended to approach the ideal value with practice in occluded protocols. To gain insight into the mechanisms of extrapolation, we modeled the response timing based on different types of threshold models. We found that occlusion was accompanied by an adaptation of model parameters (threshold time and central processing time) in a direction that suggests a strategy oriented to the interception of 1g targets at the expense of the interception of the other types of tested targets. We argue that the prediction of occluded vertical motion may incorporate an expectation of gravity effects.

Effects of colored lights, spacing between stimuli, and viewing distance on error in a depth-matching task

A previous study indicated that color of a comparison stimulus, colored light, and illumination significantly affected the error in perceived depth with binocular and monocular vision. Here, the effects of spacing between standard and comparison stimuli, viewing distance, and five colored lights were investigated. 32 Taiwanese university students in five groups were assigned to one of five colored light conditions. Spacing between comparison and standard stimuli significantly affected error in a depth-matching task. Errors increased with increased spacing. Colored light also had a significant effect; error rate in the depth-matching task under the green light condition was significantly greater than the rates under the white, yellow, and red light conditions, but the difference in error rates between blue and green and among the white, yellow, and red light conditions were not significant. The error rate at a viewing distance of 110 cm was significantly less than errors under 70- and 150-cm conditions. In addition, a two-way interaction effect was detected: viewing distance with spacing between standard and comparison stimuli.

Detection of collision events on curved trajectories: optical information from invariant rate-of-bearing change

Previous research (Andersen & Kim, 2001) has shown that a linear trajectory collision event (i.e., a collision between a moving object and an observer) is specified by objects that expand and maintain a constant bearing (the object location remains constant in the visual field). In the present study, we examined the optical information for detecting a collision event when the trajectory was of constant curvature. Under these conditions, a collision event is specified by expansion of an object and a constant rate-of-bearing change. Three experiments were conducted in which trajectory curvature and display duration were varied while time to contact, speed, and initial image position of the collision objects were maintained. The results indicated that collision detection performance decreased with an increase in trajectory curvature and decreased with a decrease in display duration, especially for highly curved trajectories. In Experiment 3, we found that the presentation of a constant rate-of-bearing change in noncollision stimuli resulted in an increase in the false alarm rate. These results demonstrate that observers can detect collision events on curved trajectories and that observers utilize bearing change information.

Temporal integration limits of stereovision in reaching and grasping

Even though there have been extensive investigations of the temporal integration limits of binocular vision in perceptual tasks, relatively little is known about temporal integration limits during the completion of visuomotor tasks. To assess the temporal integration limits of binocular disparity within the action domain, accuracy of reach kinematics in a reaching and grasping task under continuous binocular and monocular viewing conditions were compared with those obtained under alternating monocular viewing conditions with interocular delays ranging from 14 to 58 ms. Even the shortest of the interocular delays resulted in larger grip apertures than those in the continuous monocular and binocular viewing conditions. The short temporal integration interval of stereovision obtained in this study cannot be accounted for by differential visual feedback in the binocular and interocular delay conditions, nor is it likely to be a consequence of visual disruption due to the interocular delays. Our findings suggest that the visuomotor system has little tolerance to interocular delay.

Vestibular Nuclei and Cerebellum Put Visual Gravitational Motion in Context

Animal survival in the forest, and human success on the sports field, often depend on the ability to seize a target on the fly. All bodies fall at the same rate in the gravitational field, but the corresponding retinal motion varies with apparent viewing distance. How then does the brain predict time-to-collision under gravity? A perspective context from natural or pictorial settings might afford accurate predictions of gravity's effects via the recovery of an environmental reference from the scene structure. We report that embedding motion in a pictorial scene facilitates interception of gravitational acceleration over unnatural acceleration, whereas a blank scene eliminates such bias. Functional magnetic resonance imaging (fMRI) revealed blood-oxygen-level-dependent correlates of these visual context effects on gravitational motion processing in the vestibular nuclei and posterior cerebellar vermis. Our results suggest an early stage of integration of high-level visual analysis with gravity-related motion information, which may represent the substrate for perceptual constancy of ubiquitous gravitational motion.

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.