The scaling of information to action in visually guided braking

Exploring perceptual grouping by proximity principle in multistable dot lattices: Dissociation between vision-for-perception and vision-for-action

Perceptual grouping, a fundamental mechanism in our visual system, significantly influences our interpretation of and interaction with the surrounding world. This study explores the impact of the proximity principle from the perspective of the Two Visual Systems (TVS) model. The TVS model argues that the visual system comprises two distinct streams: the ventral stream, which forms the neural basis for "vision-for-perception," and the dorsal stream, which underlies "vision-for-action." We designed a perceptual grouping task using dot lattices as well as a line-orientation discrimination task. Data were collected using vocal and mouse methods for the vision-for-perception mode, and joystick and pen-paper methods for the vision-for-action mode. Each method, except for vocal, included separate blocks for right and left hands. The proximity data were fitted using exponential and power models. Linear mixed-effects models were used for the statistical analyses. The results revealed similar line-orientation discrimination accuracy across all conditions. The exponential model emerged as the best fit, demonstrating adherence to the Pure Distance Law in both perceptual modes. Sensitivity to the proximity principle was higher in the vision-for-action mode compared to the vision-for-perception. In terms of orientation biases, a strong preference for vertical orientation was observed in the vision-for-perception mode, whereas a noticeable preference toward either of the oblique orientations was detected in the vision-for-action mode. Analysis of free-drawn lines demonstrated an affordance bias in the vision-for-action mode. This suggests a remarkable tendency to perceive organizations within specific orientations that offer more affordances due to the interaction between the body postures and tools.

Higher order affordances

Affordances are opportunities for action for a given animal (or animals) in a given environment or situation. The concept of affordance has been widely adopted in the behavioral sciences, but important questions remain. We propose a new way of understanding the nature of affordances; in particular, how affordances are related to one another. We claim that many - perhaps most - affordances emerge from non-additive relations among other affordances, such that some affordances are of higher order relative to other affordances. That is, we propose that affordances form a continuous category of perceiveables that differ only in whether and how they relate to other affordances. We argue that: (1) opportunities for behaviors of all kinds can be described as affordances, (2) some affordances emerge from relations between animal and environment, whereas most affordances emerge from relations between other affordances, and (3) all affordances lawfully structure ambient energy arrays and, therefore, can be perceived directly. Our concept of higher order affordances provides a general account of behavioral phenomena that traditionally have been interpreted in terms of cognitive processes (e.g., remembering or imagining) as well as behavioral phenomena that have traditionally been interpreted in terms of cultural rules, such as conventions, or customs.

Can I catch this ball and do I know if I can? Characterizing the affordance of interceptability for oneself

In this study, we aimed to characterize the affordance of interceptability for oneself using a manual lateral interception paradigm. We asked a two-fold research question: (1) What makes a virtual ball interceptable or not? (2) How reliably can individuals perceive this affordance for oneself? We hypothesized that a spatiotemporal boundary would determine the interceptability of a ball, and that individuals would be able to perceive this boundary and make accurate perceptual judgments regarding their own interceptability. To test our hypotheses, we administered a manual lateral interception task to 15 subjects. They were first trained on the task, which was followed by two experimental sessions: action and judging. In the former, participants were instructed to intercept as many virtual balls as possible using a hand-held slider to control an on-screen paddle. In the latter session, while making interceptions, participants were instructed to call "no" as soon as they perceived a ball to be uninterceptable. Using generalized linear modeling on the data, we found a handful of factors that best characterized the affordance of interceptability. As hypothesized, distance to be covered and ball flight time shaped the boundary between interceptable and uninterceptable balls. Surprisingly, the angle of approach of the ball also co-determined interceptability. Altogether, these variables characterized the actualized interceptability. Secondly, participants accurately perceived their own ability to intercept balls on over 75% of trials, thus supporting our hypothesis on perceived interceptability. Analyses revealed that participants considered this action boundary while making their perceptual judgments. Our results imply that the perceiving and actualizing of interceptability are characterized by a combination of the same set of variables.

Targeted reaching with monocular depth information and haptic feedback: Comparing between monocular patients and normally sighted observers

Monocular blindness impairs visual depth perception, yet patients seldom report difficulties in targeted actions like reaching, walking, or driving. We hypothesized that by utilizing monocular depth information and calibrating actions with haptic feedback, monocular patients can perceive egocentric distance and perform targeted actions. We compared targeted reaching in monocular patients, monocular-viewing, and binocular-viewing normal controls. Sixty observers reached either a far or a near target, calibrating reaches to the near target with accurate or false feedback while leaving reaches to the far target uncalibrated. Reaching accuracy and precision were analyzed. Results indicated no difference in reaching accuracy between monocular patients and normal controls; all groups initially underestimated distances before until calibration. Monocular patients responded to calibration sensitively, achieving accuracy in calibrated reaches and generalizing this effect to uncalibrated distances. Thus, with monocular depth information and haptic feedback, monocular patients could perceive distance and accomplish targeted reaching.

The visual control of locomotion when stepping onto moving surfaces: A comparison of younger and older adults

Stepping between static and moving surfaces presents a locomotor challenge associated with increased injury frequency and severity in older adults. The current study evaluates younger and older adults' behaviours when overcoming challenges sampling moving walkway and escalator environments. Twelve younger adults (18-40 years, Male = 8) and 15 older adults (60-81 years, Male = 5) were examined using an integration of optoelectronic motion capture and mobile eye-tracking. Participants were investigated approaching and stepping onto a flat conveyor belt (static or moving; with or without surface (demarcation) lines). Specifically, the four conditions were: (i) static surface without demarcation lines; (ii) static surface with demarcation lines; (iii) moving surface without demarcation lines; and (iv) moving surface with demarcation lines. A two (age group) x two (surface-condition) x two (demarcation-condition) linear mixed-model revealed no main or interaction effects (p > .05) for perturbation magnitude, indicating participants maintained successful locomotion. However, different adaptive behaviours were identified between conditions with moving and accuracy demands (e.g., moving surfaces increased step length, demarcations reduced step length). Between subject effects identified differences between age groups. Older adults utilised different behaviours, such as earlier gaze transfer from the final approach walkway step location. Overall, the current study suggests that adaptive behaviours emerge relative to the environment's specific demands and the individual's action capabilities.

A Skill Acquisition Perspective on the Impact of Exergaming Technology on Foundational Movement Skill Development in Children 3-12 Years: A Systematic Review and Meta-analysis

BACKGROUND

Sedentary, digital screen time in children represents a major concern due to its detrimental effect on children's development. Nowadays, however, advances in technology allow children to actively interact with a digital screen using their whole body (e.g., exergaming), providing potential for movement learning. Exergaming technology may prove valuable in supporting children's development of foundational movement skills (FMS).

OBJECTIVE

To examine the impact of exergaming technology on the development of FMS in children 3-12 years through a skill acquisition lens.

METHODS

Systematic review and meta-analysis were conducted following the PRISMA guidelines. Web of Science, PubMed, PsycINFO and SPORTDiscus databases were searched between 2007 and 2022. Studies were eligible if they conducted an exergaming intervention to improve FMS in typically developing children aged three to twelve with a control group, using a baseline and post-intervention assessment design. FMS outcomes were pooled with a random effects model.

RESULTS

Nine trials (4 RCTs, 2 cluster RCTs and 3 non-randomized trials) of varying methodological quality (2 had low, 6 had some concerns, and 1 had a high risk of bias) were included, with a total of 783 participants. FMS outcome measures across studies comprised object control skills, locomotor skills, coordination, agility, balance and balance-related skills. The meta-analysis included showed a small positive effect in favor of the exergaming intervention (r = 0.24 [95% confidence interval: 0.11-0.36]).

CONCLUSION

Our results indicate that screen-based technology that requires an active engagement of the child can promote the development of FMS. Considering that FMS are the foundation of a child's physical, mental, health and academic development, this finding could lead to a reshaping of the perception of digital screen-based technology and the role this should play in children's lives. We speculate that the observed benefits most likely depend upon the quality of information-movement coupling specificity and the motor learning strategies built into the exergame and/or the intervention design. We do not believe this is dependent on the type of FMS being performed or the amount of practice. We recommend therefore that future research should examine how practitioners (school teachers, coaches and parents) can facilitate the interaction between a child and exergaming technology.

Keeping the driver in the loop through semi-automated or manual lane changes in conditionally automated driving

In the current study we investigated if drivers of conditionally automated vehicles can be kept in the loop through lane change maneuvers. More specifically, we examined whether involving drivers in lane-changes during a conditionally automated ride can influence critical take-over behavior and keep drivers' gaze on the road. In a repeated measures driving simulator study (n = 85), drivers drove the same route three times, each trial containing four lane changes that were all either (1) automated, (2) semi-automated or (3) manual. Each ride ended with a critical take-over situation that could be solved by braking and/or steering. Critical take-over reactions were analyzed with a linear mixed model and parametric accelerated failure time survival analysis. As expected, semi-automated and manual lane changes throughout the ride led to 13.5% and 17.0% faster maximum deceleration compared to automated lane changes. Additionally, semi-automated and manual lane changes improved the quality of the take-over by significantly decreasing standard deviation of the steering wheel angle. Unexpectedly, drivers in the semi-automated condition were slowest to start the braking maneuver. This may have been caused by the drivers' confusion as to how the semi-automated system would react. Additionally, the percentage gaze off-the-road was significantly decreased by the semi-automated (6.0%) and manual (6.6%) lane changes. Taken together, the results suggest that semi-automated and manual transitions may be an alarm-free instrument which developers could use to help maintain drivers' perception-action loop and improve automated driving safety.

Time for Space and the Stability of Prospective Control: Reaching-to-Grasp Gibson

Gibson formulated an approach to goal-directed behavior using prospective information in the context of visually guided locomotion and manual behavior. The former was Gibson's paradigm case, but it is the rapidity of targeted reaching that has provided the special challenge for stable control. Recent treatments of visually guided reaching assume that internal forward models are required to generate stable behavior given delays caused by neural transmission times. Internal models are representations of the sort eschewed by Gibson in favor of prospective information. Reaching is usually described as guided using relative distances of hand and target, but prospective information is usually temporal rather than spatial. We describe proportional rate control models that incorporate time dimensioned prospective information and show they remain stable in the face of delays. The use of time-dimensioned prospective information removes the need for internal models for stable behavior despite neural transmission delays and allows Gibson's approach to prevail.

The Influence of Perceptual-Motor Variability on the Perception of Action Boundaries for Reaching in a Real-World Setting

The ability to accurately perceive the extent over which one can act is requisite for the successful execution of visually guided actions. Yet, like other outcomes of perceptual-motor experience, our perceived action boundaries are not stagnant, but in constant flux. Hence, the perceptual systems must account for variability in one's action capabilities in order for the perceiver to determine when they are capable of successfully performing an action. Recent work has found that, after reaching with a virtual arm that varied between short and long each time they reach, individuals determined their perceived action boundaries using the most liberal reaching experience. However, these studies were conducted in virtual reality, and the perceptual systems may handle variability differently in a real-world setting. To test this hypothesis, we created a modified orthopedic elbow brace that mimics injury in the upper limb by restricting elbow extension via remote control. Participants were asked to make reachability judgments after training in which the maximum extent of their reaching ability was either unconstricted, constricted or variable over several calibration trials. Findings from the current study did not conform to those in virtual reality; participants were more conservative with their reachability estimates after experiencing variability in a real-world setting.

How far can I reach? The perception of upper body action capabilities in Parkinson's disease

Successful interaction within the environment is contingent upon one’s ability to accurately perceive the extent over which they can successfully perform actions, known as action boundaries. Healthy young adults are accurate in estimating their action boundaries and can flexibly update them to accommodate stable changes in their action capabilities. However, there are conditions in which motor abilities are subject to variability over time such as in Parkinson’s disease (PD). PD impairs the ability to perform actions and can lead to variability in perceptual-motor experience, but the effect on the perceptions of their action boundaries remains unknown. This study investigated the influence of altered perceptual-motor experience during PD, on the perceptions of action boundaries for reaching, grasping, and aperture passing. Thirty participants with mild-to-moderate idiopathic PD and 26 healthy older adults provided estimates of their reaching, grasping, and aperture-passing ability. Participants’ estimates were compared with their actual capabilities. There was no evidence that individuals with PD’s perceptions were less accurate than those of healthy controls. Furthermore, there was some evidence for more conservative estimates than seen in young healthy adults in reaching (both groups) and aperture passing (PD group). This suggests that the ability to judge action capabilities is preserved in mild to moderate PD.

It's in your hands: How variable perception affects grasping estimates in virtual reality

Successful interaction within one’s environment is contingent upon one’s ability to accurately perceive the extent over which actions can be performed, referred to as action boundaries. As our possibilities for action are subject to variability, it is necessary for individuals to be able to update their perceived action boundaries to accommodate for variance. While research has shown that individuals can update their action boundaries to accommodate for variability, it is unclear how the perceptual system calibrates to this variance to inform our action boundaries. This study investigated the influence of perceptual motor variability by analysing the effect of random and systematic variability on perceived grasp ability in virtual reality. Participants estimated grasp ability following perceptual-motor experience with a constricted, normal, extended, or variable grasp. In Experiment 1, participants experienced all three grasping abilities (constricted, normal, extended) 33% of the time. In Experiment 2 participants experienced the constricted and normal grasps 25% of the time, and the extended grasp 50% of the time. The results indicated that when perceptual-motor feedback is inconsistent, the perceptual system disregards the frequency of perceptual-motor experience with the different action capabilities and considers each action capability experienced as a type, and subsequently calibrates to the average action boundary experienced by type.

Control of visually guided braking using constant-[Formula: see text] and proportional rate

This study investigated the optical information and control strategies used in visually guided braking. In such tasks, drivers exhibit two different braking behaviors: impulsive braking and continuously regulated braking. We designed two experiments involving a simulated braking task to investigate these two behaviors. Participants viewed computer displays simulating an approach along a linear path over a textured ground surface toward a set of road signs. The task was to use a joystick as a brake to stop as close as possible to the road signs. Our results showed that participants relied on a weak constant-[Formula: see text] strategy (Bingham 1995) when regulating the brake impulsively. They used discrete [Formula: see text] values as critical values and they regulated the brake so as not to let [Formula: see text] fall below these values. Our results also showed that proportional rate control (Anderson and Bingham 2010, 2011) is used in continuously regulated braking. Participants initiated braking at a certain proportional rate value and controlled braking so as to maintain that value constant during the approach. Proportional rate control is robust because the value can fluctuate within a range to yield good performance. We argue that proportional rate control unifies the information-based approach and affordance-based approach to visually guided braking.

Anxiety Influences the Perceptual-Motor Calibration of Visually Guided Braking to Avoid Collisions

We investigated whether anxiety influences perceptual-motor calibration in a braking to avoid a collision task. Participants performed either a discrete braking task (Experiment 1) or a continuous braking task (Experiment 2), with the goal of stopping before colliding with a stop sign. Half of participants performed the braking task after an anxiety induction. We investigated whether anxiety reduced the frequency of crashing and if it influenced the calibration of perception (visual information) and action (brake pressure) dynamically between-trials in Experiment 1 and within-trials in Experiment 2. In the discrete braking task, anxious participants crashed less often and made larger corrective adjustments trial-to-trial after crashing, suggesting that the influence of anxiety on behavior did not occur uniformly, but rather dynamically with anxiety amplifying the reaction to previous crashes. However, when performing continuous braking, anxious participants crashed more often, and their within-trial adjustments of deceleration were less related to visual information compared to controls. Taken together, these findings suggest that the timescale and nature of the task mediates the influence of anxiety on the performance of goal-directed actions.

Perceptual Modification of the Built Environment to Influence Behavior Associated with Physical Activity: Quasi-Experimental Field Studies of a Stair Banister Illusion

BACKGROUND

Re-engineering the built environment to influence behaviors associated with physical activity potentially provides an opportunity to promote healthier lifestyles at a population level. Here we present evidence from two quasi-experimental field studies in which we tested a novel, yet deceptively simple, intervention designed to alter perception of, and walking behavior associated with, stairs in an urban area.

OBJECTIVES

Our objectives were to examine whether adjusting a stair banister has an influence on perceptions of stair steepness or on walking behavior when approaching the stairs.

METHODS

In study 1, we asked participants (n = 143) to visually estimate the steepness of a set of stairs viewed from the top, when the stair banister was adjusted so that it converged with or diverged from the stairs (± 1.91°) or remained neutral (± 0°). In study 2, the walking behavior of participants (n = 36) was filmed as they approached the stairs to descend, unaware of whether the banister converged, diverged, or was neutral.

RESULTS

In study 1, participants estimated the stairs to be steeper if the banister diverged from, rather than converged with, the stairs. The effect was greater when participants were unaware of the adjustment. In study 2, walking speed was significantly slower when the banister diverged from, rather than converged with, the stairs.

CONCLUSIONS

These findings encourage us to speculate about the potential to economically re-engineer features of the built environment to provide opportunities for action (affordances) that invite physical activity behavior or even promote safer navigation of the environment.

When a Fly Ball Is Out of Reach: Catchability Judgments Are Not Based on Optical Acceleration Cancelation

The optical acceleration cancelation (OAC) strategy, based on Chapman's (1968) analysis of the outfielder problem, has been the dominant account for the control of running to intercept fly balls approaching head on. According to the OAC strategy, outfielders will arrive at the interception location just in time to catch the ball when they keep optical acceleration zero. However, the affordance aspect of this task, that is, whether or not an approaching fly ball is catchable, is not part of this account. The present contribution examines whether the scope of the OAC strategy can be extended to also include the affordance aspect of running to catch a fly ball. This is done by considering a fielder's action boundaries (i.e., maximum running velocity and -acceleration) in the context of the OAC strategy. From this, only when running velocity is maximal and optical acceleration is non-zero, a fielder would use OAC to perceive a fly ball as uncatchable. The present contribution puts this hypothesis to the test. Participants were required to try to intercept fly balls projected along their sagittal plane. Some fly balls were catchable whereas others were not. Participants were required to catch as many fly balls as possible and to call 'no' when they perceived a fly ball to be uncatchable. Participants' running velocity and -acceleration at the moment of calling 'no' were examined. Results showed that participants' running velocity was submaximal before or while calling 'no'. Also running acceleration was often submaximal. These results cannot be explained by the use of OAC in judging catchability and ultimately call for a new strategy of locomotor control in running to catch a fly ball.

The embodied dynamics of perceptual causality: a slippery slope?

In Michotte's launching displays, while the launcher (object A) seems to move autonomously, the target (object B) seems to be displaced passively. However, the impression of A actively launching B does not persist beyond a certain distance identified as the "radius of action" of A over B. If the target keeps moving beyond the radius of action, it loses its passivity and seems to move autonomously. Here, we manipulated implied friction by drawing (or not) a surface upon which A and B are traveling, and by varying the inclination of this surface in screen- and earth-centered reference frames. Among 72 participants (n = 52 in Experiment 1; n = 20 in Experiment 2), we show that both physical embodiment of the event (looking straight ahead at a screen displaying the event on a vertical plane vs. looking downwards at the event displayed on a horizontal plane) and contextual information (objects moving along a depicted surface or in isolation) affect interpretation of the event and modulate the radius of action of the launcher. Using classical mechanics equations, we show that representational consistency of friction from radius of action responses emphasizes the embodied nature of frictional force in our cognitive architecture.

Drivers' decision-making when attempting to cross an intersection results from choice between affordances

In theory, a safe approach to an intersection implies that drivers can simultaneously manage two scenarios: they either choose to cross or to give way to an oncoming vehicle. In this article we formalize the critical time for safe crossing (CT_cross) and the critical time for safe stopping (CT_stop) to represent crossing and stopping possibilities, respectively. We describe these critical times in terms of affordances and empirically test their respective contribution to the driver's decision-making process. Using a driving simulator, three groups of participants drove cars with identical acceleration capabilities and different braking capabilities. They were asked to try to cross an intersection where there was an oncoming vehicle, if they deemed the maneuver to be safe. If not, they could decide to stop or, as a last resort, make an emergency exit. The intersections were identical among groups. Results showed that although the crossing possibilities (CT_cross) were the same for all groups, there were between-group differences in crossing frequency. This suggests that stopping possibilities (CT_stop) play a role in the driver's decision-making process, in addition to the crossing possibilities. These results can be accounted for by a behavioral model of decision making, and provide support for the hypothesis of choice between affordances.

Guiding locomotion in complex, dynamic environments

Locomotion in complex, dynamic environments is an integral part of many daily activities, including walking in crowded spaces, driving on busy roadways, and playing sports. Many of the tasks that humans perform in such environments involve interactions with moving objects-that is, they require people to coordinate their own movement with the movements of other objects. A widely adopted framework for research on the detection, avoidance, and interception of moving objects is the bearing angle model, according to which observers move so as to keep the bearing angle of the object constant for interception and varying for obstacle avoidance. The bearing angle model offers a simple, parsimonious account of visual control but has several significant limitations and does not easily scale up to more complex tasks. In this paper, I introduce an alternative account of how humans choose actions and guide locomotion in the presence of moving objects. I show how the new approach addresses the limitations of the bearing angle model and accounts for a variety of behaviors involving moving objects, including (1) choosing whether to pass in front of or behind a moving obstacle, (2) perceiving whether a gap between a pair of moving obstacles is passable, (3) avoiding a collision while passing through single or multiple lanes of traffic, (4) coordinating speed and direction of locomotion during interception, (5) simultaneously intercepting a moving target while avoiding a stationary or moving obstacle, and (6) knowing whether to abandon the chase of a moving target. I also summarize data from recent studies that support the new approach.

A perceptual-motor deficit predicts social and communicative impairments in individuals with autism spectrum disorders

Individuals with autism spectrum disorders (ASDs) have known impairments in social and motor skills. Identifying putative underlying mechanisms of these impairments could lead to improved understanding of the etiology of core social/communicative deficits in ASDs, and identification of novel intervention targets. The ability to perceptually integrate one's physical capacities with one's environment (affordance perception) may be such a mechanism. This ability has been theorized to be impaired in ASDs, but this question has never been directly tested. Crucially, affordance perception has shown to be amenable to learning; thus, if it is implicated in deficits in ASDs, it may be a valuable unexplored intervention target. The present study compared affordance perception in adolescents and adults with ASDs to typically developing (TD) controls. Two groups of individuals (adolescents and adults) with ASDs and age-matched TD controls completed well-established action capability estimation tasks (reachability, graspability, and aperture passability). Their caregivers completed a measure of their lifetime social/communicative deficits. Compared with controls, individuals with ASDs showed unprecedented gross impairments in relating information about their bodies' action capabilities to visual information specifying the environment. The magnitude of these deficits strongly predicted the magnitude of social/communicative impairments in individuals with ASDs. Thus, social/communicative impairments in ASDs may derive, at least in part, from deficits in basic perceptual-motor processes (e.g. action capability estimation). Such deficits may impair the ability to maintain and calibrate the relationship between oneself and one's social and physical environments, and present fruitful, novel, and unexplored target for intervention.

Direct perception of action-scaled affordances: the shrinking gap problem

The aim of this study was to investigate the perception of possibilities for action (i.e., affordances) that depend on one's movement capabilities, and more specifically, the passability of a shrinking gap between converging obstacles. We introduce a new optical invariant that specifies in intrinsic units the minimum locomotor speed needed to safely pass through a shrinking gap. Detecting this information during self-motion requires recovering the component of the obstacles' local optical expansion attributable to obstacle motion, independent of self-motion. In principle, recovering the obstacle motion component could involve either visual or non-visual self-motion information. We investigated the visual and non-visual contributions in two experiments in which subjects walked through a virtual environment and made judgments about whether it was possible to pass through a shrinking gap. On a small percentage of trials, visual and non-visual self-motion information were independently manipulated by varying the speed with which subjects moved through the virtual environment. Comparisons of judgments on such catch trials with judgments on normal trials revealed both visual and non-visual contributions to the detection of information about minimum walking speed.

Reconsidering the role of movement in perceiving action-scaled affordances

Many locomotor tasks require actors to choose among different categories of action, such as when deciding whether to cross the street in front of an approaching vehicle or wait until it passes. In such cases, the actor's locomotor capabilities partly determine which actions are possible, and therefore must be taken into account. The present study was designed to re-evaluate the claim that people do not know their locomotor capabilities until they begin moving because they rely entirely on information that is picked up "on the fly" (Oudejans, Michaels, Bakker, & Dolné, 1996). Three experiments were conducted in which participants judged while stationary or moving whether it was within their capabilities to catch a fly ball or pass through a shrinking gap. The main finding was that judgments were equally accurate regardless of whether participants were stationary or allowed to move for a brief period. We conclude that stationary and moving actors know their locomotor capabilities equally well, and that actors do not rely entirely on information that is picked up on the fly.

Look before you leap: jumping ability affects distance perception

Previous research has demonstrated that changing perceivers' action capabilities can affect their perception of the extent over which an action is performed. In the current study, we manipulated jumping ability by having participants wear ankle weights and examined the influence of this manipulation on the perception of jumpable and un-jumpable extents. When wearing ankle weights, jumpable gaps appeared longer than when not wearing ankle weights; however, for un-jumpable gaps, there was no difference in the apparent gap extent, regardless of whether the participant was wearing ankle weights. This suggests that the perception of a jumpable extent is affected by one's action boundary for jumping, but only if jumping is an action that can be performed over the extent.

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.

The contribution of stereo vision to the control of braking

In this study the contribution of stereo vision to the control of braking in front of a stationary target vehicle was investigated. Participants with normal (StereoN) and weak (StereoW) stereo vision drove a go-cart along a linear track towards a stationary vehicle. They could start braking from a distance of 4, 7, or 10m from the vehicle. Deceleration patterns were measured by means of a laser. A lack of stereo vision was associated with an earlier onset of braking, but the duration of the braking manoeuvre was similar. During the deceleration, the time of peak deceleration occurred earlier in drivers with weak stereo vision. Stopping distance was greater in those lacking in stereo vision. A lack of stereo vision was associated with a more prudent brake behaviour, in which the driver took into account a larger safety margin. This compensation might be caused either by an unconscious adaptation of the human perceptuo-motor system, or by a systematic underestimation of distance remaining due to the lack of stereo vision. In general, a lack of stereo vision did not seem to increase the risk of rear-end collisions.

Rapid recalibration based on optic flow in visually guided action

Action capabilities are always subject to limits. Whether on foot or in a vehicle, people can only move so fast, slow down so quickly, and turn so sharply. The successful performance of almost any perceptual-motor task requires actors to learn and continually relearn their ever-changing action capabilities. Such learning can be considered an example of perceptual-motor calibration. The present study includes two experiments designed to address basic questions about the nature of this calibration process. Subjects performed a simulated braking task, using a foot pedal to slow down to a stop in front of an obstacle in the path of motion. At one point in the experiment, the strength of the brake was increased or decreased unbeknownst to subjects, and behavior before and after the change in brake strength was analyzed for evidence of recalibration. Experiment 1 showed that actors rapidly recalibrate following a change in brake dynamics, even when they are unaware of the change. In Experiment 2, the scene turned black one second after braking was initiated. Subjects still recalibrated following the change in brake strength, suggesting that information in the sensory consequences of the initial brake adjustment is sufficient for recalibration, even in the absence of feedback about the outcome (i.e., in terms of final position error) of the task. Discussion focuses on the critical but often overlooked role of calibration in continuously controlled visually guided action, and the nature of the information used for recalibration.

Learning to control collisions: The role of perceptual attunement and action boundaries

The authors investigated the role of perceptual attunement in an emergency braking task in which participants waited until the last possible moment to slam on the brakes. Effects of the size of the approached object and initial speed on the initiation of braking were used to identify the optical variables on which participants relied at various stages of practice. In Experiments 1A and 1B, size and speed effects that were present early in practice diminished but were not eliminated as participants learned to initiate braking at a rate of optical expansion that varied with optical angle. When size and speed were manipulated together in Experiment 2, the size effect was quickly eliminated, and participants learned to use a 3rd optical variable (global optic flow rate) to nearly eliminate the speed effect. The authors conclude that perceptual attunement depends on the range of practice conditions, the availability of information, and the criteria for success.