Athletic experience influences shoulder rotations when running through apertures

The effect of experience on the perception of affordances for aperture crossing in cycling

To ride successfully and safely, cyclists must perceive and act on the affordances that are available in a given situation. This study investigated whether experience in perceiving and acting with respect to a person-plus-object system would influence whether and how a person choses to cross an aperture of different widths, especially in relation to their maximal action capabilities. We also explore whether the distribution of action modes reflects this effect. We examined the performance (i.e., the probability of successfully crossing the aperture) and the decision (i.e., the probability of attempting to cross the aperture) of 8 experienced cyclists and 16 occasional cyclists in an aperture crossing task. In term of performance, experienced cyclists demonstrated greater ability to cross narrower apertures than occasional cyclists, but there were no such differences when aperture width was scaled to maximal action capabilities. In term of decision, both experienced and occasional cyclists tended to over-estimate their abilities, but the experienced cyclists did so to a greater extent. Our findings indicate that experience improves the ability to perform more complex tasks due to utilizing a wider repertoire of actions, but not necessarily the ability to perceive and actualize (action-scaled) affordances.

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.

Affordance-based control of braking in cycling: Experience reveals differences in the style of control

We investigated whether in an in-situ collision avoidance experiment cyclists regulate braking by adopting an affordance-based control strategy. Within an affordance-based control strategy for braking, deceleration is controlled relative to the maximum achievable deceleration rather than by nulling out deviations from ideal deceleration, and potentially allowing for different braking styles. Twenty active- and eighteen inactive-cyclists were asked to cycle on a straight path in an indoor gym and to stop as close as possible in front of a stationary obstacle. Maximum achievable deceleration was manipulated by loading the bike: no-load, load-5 kg, and load-10 kg. Two approach distances were used to vary cycling speed. Participants in both groups stopped farther from the obstacle when approaching with long- than short-initial distance conditions. No systematic effects of loading on braking performance and control were found across the two groups. However, both groups did increase the magnitude of brake adjustments as ideal deceleration increased and got closer to the action boundary, even when current deceleration approached the ideal deceleration. This indicates that participants adopted an affordance-based control strategy for braking. Two braking styles were identified: an aggressive style, characterized by a late braking onset and a high, steep peak in ideal deceleration, and a conservative style, characterized by an early braking onset and gradual, linear increase in ideal deceleration. The aggressive braking style was more prevalent among the active-cyclists. We suggest that the braking styles emerge from differences in calibration between information and action. The novelty of our work lies in confirming that cyclists adopt an affordance-based control strategy in an in-situ experiment and in demonstrating and explicating how affordance-based control can incorporate the emergence of different styles of braking.

Created stepping-stone configurations depend on task constraints

Previous studies have shown that choices about how to configure stepping-stones to be used as playground or exercise equipment reflect a person's action capabilities. In two experiments, we investigated whether choices about how to configure stepping-stones to be used as a path for locomotion additionally reflect the goals for which or the constraints under which the path is to be used. In Experiment 1, participants created stepping-stone configurations (with rubber mats) that would allow them to cross a given space quickly, comfortably, or carefully. Configurations in the "Quickly" condition consisted of fewer mats, and longer mean (linear) distances between mats, and greater "challenge" (relative to maximum stepping distance) than in the other two conditions. In Experiment 2, participants created stepping-stone configurations that would be fun to use or that would be easy to use to cross a given space. Configurations in the "Fun" condition consisted of more mats, longer linear distances between mats, and greater "challenge" than those in the "Easy" condition. Moreover, paths in the "Fun" condition were also wider, longer, and exhibited larger changes in distances and angles between consecutive mats than in the "Easy" condition. The results are discussed both in terms of implications for understanding affordances and for the design of stepping-stone paths.

Perception of Affordances in Female Volleyball Players: Serving Short versus Serving to the Sideline

Purpose: We investigated youth volleyball players' perception of affordances for different types of serves. Methods: Participants were separated into Less Experienced (n = 13, maximum of 3 years of competitive volleyball experience) and More Experienced (n = 11, minimum of 4 years of competitive volleyball experience) groups. In the Sideline Condition, participants were asked to report the narrowest gap, relative to either the left or right sideline, into which they could serve the ball. In the Short Condition, participants were asked to report the narrowest gap, relative to the net, into which they could serve the ball. Participants then attempted to serve into their reported gaps. Results: The proportion of successful serves was greater for the More Experienced group than for the Less Experienced group, but a statistically significant interaction revealed that this was true only when performing sideline serves. As expected, reported servable gaps were larger for the Short Serve condition (M = 3.66 m, SD = 0.67 m) than for the Sideline Serve condition (M = 1.93 m, SD = 0.71 m), F(1, 22) = 80.45, p < .001, partial η2 = 0.79. Conclusions: Our study extends previous work to a different sport (volleyball) and to different sport-specific actions (serving the ball). The finding that perceived minimum servable gap sizes were larger for short serves than for sideline serves is consistent with differences in the constraints operating on the two types of serves in the context of game play.

A systematic review of perception of affordances for the person-plus-object system

Human behavior often involves the use of an object held by or attached to the body, which modifies the individual's action capabilities. Moreover, most everyday behaviors consist of sets of behaviors that are nested over multiple spatial and temporal scales, which require perceiving and acting on nested affordances for the person-plus-object system. This systematic review investigates how individuals attune to information about affordances involving the person-plus-object system and how they (re)calibrate their actions to relevant information. We analyzed 71 articles-34 on attunement and 37 on (re)calibration with healthy participants-that experimentally investigated the processes involved in the perception of affordances for the person-plus-object system (including attunement, calibration, and recalibration). With respect to attunement, objects attached to the body create a multiplicity of affordances for the person-plus-object system, and individuals learned (1) to detect information about affordances of (and for) the person-plus-object system in a task and (2) to choose whether, when, and how to exploit those affordances to perform that task. Concerning (re)calibration, individuals were able (1) to quickly scale their actions in relation to the (changed) action capabilities of the person-plus-object system and (2) to perceive multiple functionally equivalent ways to exploit the affordances of that system, and these abilities improved with practice. Perceiving affordances for the person-plus-object system involves learning to detect the information about such affordances (attunement) and the scaling of behaviors to such information (calibration). These processes imply a general ability to incorporate an object attached to the body into an integrated person-plus-object system.

Generalizing the optic flow equalization control law to an asymmetrical person-plus-object system

Visually guided action in humans occurs in part through the use of control laws, which are dynamical equations in which optical information modulates an actor's interaction with their environment. For example, humans locomote through the center of a corridor by equalizing the speed of optic flow across their left and right fields of view. This optic flow equalization control law relies on a crucial assumption: that the shape of the body relative to the eyes is laterally symmetrical. Humans engaging in tool use are often producing person-plus-object systems that are not laterally symmetrical, such as when they hold a tool, bag, or briefcase in one hand, or when they drive a vehicle. This experiment tests a new generalized control law for centered steering that accounts for asymmetries produced by external tool use. Participants held an asymmetrical bar and centered themselves within a virtual moving hallway while the speed of the virtual walls were systematically changed. The results demonstrate that humans engaging with an asymmetrical tool can (1) perceive the asymmetry of a person-plus-object system, (2) use that information to modulate the use of optic flow equalization control laws for centered steering, and (3) functionally incorporate the asymmetrical tool into their perception-action system to successfully navigate their environment.

The effect of fatigue on climbing fluidity and hand movements

In rock climbing, climbers use their arms to regulate their posture on the wall, which can lead to localised muscle fatigue. Evidence shows fatigue is the primary cause of falls, but little is known about how fatigue specifically affects climbing rhythm and hand movements. The present study examined climbing fluidity and hand movements on an indoor climbing wall before and after a specific fatiguing protocol. Seventeen climbers completed three repetitions of a challenging climbing route (21 on Ewbank scale) with different levels of localised arm fatigue. Climbers' movements were tracked using 3D motion capture, and their hand actions assessed using notational analysis. Seventy markers were used to create 15 rigid body segments and the participants' centre of mass. The global entropy index was calculated on the path of the participants' centre of mass. Climbers fell more often when fatigued, but there were no significant differences in hip jerk or global entropy index when fatigued. No significant differences were found between the number of exploratory or performatory hand movements with different amounts of fatigue. The results suggest that localised arm fatigue affects a climber's ability to prevent themselves from falling, but it does not specifically affect their fluidity.

Training for walking through an opening improves collision avoidance behavior in subacute patients with stroke: a randomized controlled trial

PURPOSE

Paretic side collisions frequently occur in stroke patients, especially while walking through narrow spaces. We determined whether training for walking through an opening (T-WTO) while entering from the paretic side would improve collision avoidance behavior and prevent falls after 6 months.

MATERIALS AND METHODS

Thirty-eight adults with moderate-to-mild hemiparetic gait after stroke who were hospitalized in a rehabilitation setting were randomly allocated to the T-WTO (n = 20) or regular rehabilitation (R-Control; n = 18) program. Both groups received five sessions of 40 min per week, for three weeks total. T-WTO included walking through openings of various widths while rotating with the paretic side in front, and R-Control involved normal walking without body rotation. Obstacle avoidance ability, 10-m walking test, timed Up and Go test, Berg Balance Scale, Activities-specific Balance Confidence, the perceptual judgment of passability, and fall incidence were assessed.

RESULTS

Collision rate and time to passage of the opening in obstacle avoidance task significantly improved in the T-WTO group compared with those in the R-Control group. Contrast, T-WTO did not lead to significant improvements in other outcomes.

CONCLUSIONS

T-WTO improved efficiency and safety in managing subacute stroke patients. Such training could improve patient outcomes/safety because of the paretic body side during walking.

CLINICAL TRIAL REGISTRATION NO.

R000038375 UMIN000033926.

CrossFit® open performance is affected by the nature of past competition experiences

Purpose

To examine the relationships between past competition performances and 2020 CrossFit® Open (CFO) performance.

Methods

A random selection from the top one thousand athletes (n = 220, 28.5 ± 4.4 years, 178 ± 7 cm, 87.5 ± 10.2 kg) were selected for this study. Overall and weekly performances (including ranks and scores) of the 2020 CFO, as well as overall ranks from all previous CFO, regional, and Games™ competitions in which they competed, were recorded from their publicly available online profile. The highest, lowest, average, and standard deviation (SD) of past rankings, as well as participation statistics (i.e., years since first appearance, total and consecutive appearances, and participation rate), were calculated for each competition stage. Relationships were then assessed between 2020 CFO performance and all past competition experience variables by calculating Kendall’s tau (τ) correlation coefficients and Bayes factors (BF₁₀).

Results

Overall and weekly ranking of the 2020 CFO was extremely favored (p < 0.001, BF₁₀ > 100) to be related to the athlete’s highest previous CFO rank (τ = 0.26–0.39) and individual regional appearances (τ = − 0.26 to − 0.34), as well as individual Games™ appearances (overall and for weeks 1, 3, and 4; τ = − 0.20 to − 0.22, p < 0.001, BF₁₀ > 100). Evidence for all other significant relationships ranged from moderate to very strong (p < 0.05, BF₁₀ = 3–100) and varied among specific 2020 CFO workouts. Few associations were noted for team competition experience, and these were generally limited to Games™ appearances (τ = − 0.12 to − 0.18, p < 0.05, BF₁₀ = 3.3–100).

Conclusions

Although specific relationships were found between 2020 CFO performance and individual appearances at regional and Games™ competitions, the most consistent relationships were seen with participation and ranking in past CFO competitions.

Perception of Affordances in Soccer: Kicking for Power Versus Kicking for Precision

Purpose: We investigated youth soccer players' perception of affordances for different types of kicks. Method: In the Power task, players judged the maximum distance they could kick the ball. In the Precision task, players judged how close to a designated target line they could kick the ball. Following judgments, players performed each task. Both judgments and performance were assessed immediately before and immediately after players competed in a regulation soccer match, thereby permitting us to assess possible effects of long-term experience on perceptual sensitivity to short-term changes in ability. We compared players from two league groups: U16 (mean age = 15.45 years, SD = 0.52 years) versus U18 (mean age = 17.55 years, SD = 0.52 years). Results: As expected, for the Power task actual kicking ability was greater for the U18 group (p < .05). In statistically significant interactions, we found that judgments of Power kicking ability differed before versus after match play, but only for the U16 group. We found no statistically significant effects for the Precision task. Conclusions: We identified interactions between long-term and short-term soccer experience which revealed that the effects of long-term experience on affordance perception were not general. Two additional years of playing experience (in the U18 group, relative to the U16 group) did not lead to an overall improvement in the perception of kicking-related affordances. Rather, variation in long-term experience was associated with changes in affordance perception which were situation-specific, being manifested only after playing a soccer match, and not before.

Experience-Dependent Modulation of Rubber Hand Illusion in Badminton Players

Badminton players have a plastic modification of their arm representation in the brain due to the prolonged use of their racket. However, it is not known whether their arm representation can be altered through short-term visuotactile integration. The neural representation of the body is easily altered when multiple sensory signals are integrated in the brain. One of the most popular experimental paradigms for investigating this phenomenon is the "rubber hand illusion." This study was designed to investigate the effect of prolonged use of a racket on the modulation of arm representation during the rubber hand illusion in badminton players. When badminton players hold the racket, their badminton experience in years is negatively correlated with the magnitude of the rubber hand illusion. This finding suggests that tool embodiment obtained by the prolonged use of the badminton racket is less likely to be disturbed when holding the racket.

Perception of Affordances for Vertical and Horizontal Jumping in Children: Gymnasts Versus Non-Athletes

Purpose: We investigated the perception of affordances for vertical jumping-and-reaching and horizontal jumping by children. Method: In the horizontal task, children were asked to judge their ability in the standing long jump. In the vertical task, children were asked to judge the height of a ball that they could run to, jump up, and reach with their fingertips. Following judgments, children performed both types of jumps. We compared gymnasts (children with at least 2 years of gymnastics training; 7.92 ± 0.91 years) versus children with no competitive athletic experience (7.74 ± 0.86 years). Results: As expected, actual ability was greater in gymnasts than in non-athletes, for both types of jump (each p < .001). We separately analyzed Constant Error and Absolute Error of judgments (relative to actual performance). Results revealed that gymnasts tended toward underestimation, while non-athletes tended toward overestimation. Absolute error differed between tasks for the non-athletes (p < .001), but for the gymnasts the difference between conditions was not significant (p = .25). Absolute error differed between groups for vertical jump-and-reach (p < .01) but not for horizonal jump (p = .17). Conclusions: Gymnastics experience was associated with a generalized tendency for children to underestimate their jumping ability. In addition, gymnastics experience was associated with judgment accuracy that was consistent across tasks. The results reveal that gymnastics training is associated with changes in athletic ability, but also with changes in the perception of affordances.

The influence of skill and task complexity on perception of nested affordances

This study investigated how skill level and task complexity influence the calibration of perception–action and particularly how close an individual acts relative to his or her maximal action capabilities. Complexity was manipulated between two (Touch, Grasp) and more than two (Removing, Moving Up) nested affordance conditions. For all conditions, we examined whether advanced climbers had greater maximal action capabilities than intermediate climbers or whether they better scaled their action (i.e., acted nearer to their maximal action capabilities) or both. Eleven intermediate and 11 advanced male climbers were first asked to estimate the maximum distance that they could reach a climbing hold. The hold was moved along a slide and fixed once requested by the participant; subsequently, the distance to the starting hold was measured. After each estimation, the participant was required to execute the climbing action. After four estimation-action trials in each of the four conditions, the maximal action capability (i.e., actual maximal reaching distance) was determined. Advanced climbers demonstrated greater actual maximal reaching distances than intermediate climbers for all conditions, but they only estimated greater maximal reaching distances for the more complex conditions, which featured more than two nested affordances. When estimated maximal reaching distances were scaled to actual maximal reaching distances, advanced climbers did not differ from intermediate climbers for any condition, and there were no differences between conditions. Our findings indicate that expertise was a function of greater action capabilities, but not due to the accuracy of calibration.

Workout Pacing Predictors of Crossfit® Open Performance: A Pilot Study

To observe workout repetition and rest interval pacing strategies and determine which best predicted performance during the 2016 CrossFit® Open, five male (34.4 ± 3.8 years, 176 ± 5 cm, 80.3 ± 9.7 kg) and six female (35.2 ± 6.3 years, 158 ± 7 cm, 75.9 ± 19.3 kg) recreational competitors were recruited for this observational, pilot study. Exercise, round, and rest time were quantified via a stopwatch for all competitors on their first attempt of each of the five workouts. Subsequently, pacing was calculated as a repetition rate (repetitions·s^-1) to determine the fastest, slowest, and average rate for each exercise, round, and rest interval, as well as how these changed (i.e., slope, Δ rate / round) across each workout. Spearman’s rank correlation coefficients indicated that several pacing variables were significantly (p < 0.05) related to performance on each workout. However, stepwise regression analysis indicated that the average round rate best predicted (p < 0.001) performance on the first (R² = 0.89), second (R² = 0.99), and fifth (R² = 0.94) workouts, while the competitors’ rate on their slowest round best predicted workout three performance (R² = 0.94, p < 0.001). The wall ball completion rate (R² = 0.89, p = 0.002) was the best predictor of workout four performance, which was improved by 9.8% with the inclusion of the deadlift completion rate. These data suggest that when CrossFit^® Open workouts consist of multiple rounds, competitors should employ a fast and sustainable pace to improve performance. Otherwise, focusing on one or two key exercises may be the best approach.

Predicting aperture crossing behavior from within-trial metrics of motor control reliability

Actors utilize intrinsically scaled information about their geometric and dynamic properties when perceiving their ability to pass through openings. Research about dynamic factors of affordance perception have shown that the reliability of a given movement, or the precision of one's motor control for that movement, increase the buffer space used when interacting with the environment. While previous work has assessed motor control reliability as a person-level variable (i.e., behavior is aggregated across many trials), the current study assessed how characteristics of motor control and movement reliability within a single trial impact real-time action strategies for passing through apertures. Participants walked 5 m and then passed through apertures of various widths while their motions were tracked. For each trial, we collected walking time-series data, then calculated the magnitude and complexity of the lateral sway. Assessing two behavioral measures of the buffer, we found that trial-level metrics of motor control reliability, in addition to the person-level metrics previously studied, significantly predicted the buffer on each trial. This study supports previous claims that actors pick up real-time information about their dynamic capabilities in order to perceive and act within their environment. Further, the study recommends that future affordance research consider trial-level movement data, including nonlinear analyses that inform the pattern and structure of motor control reliability.

How Does a Walker Pass Between Two People Standing in Different Configurations? Influence of Personal Space on Aperture Passing Methods

Most studies on aperture passability focus on aperture passing involving non-human physical objects. In this study, we examined experimentally how participants pass between two box-shaped frames and between the same frames, each with a human confederate in it, facing various directions. Seven configuration conditions were set up, six of which differed in terms of the human confederates’ sets of directions in the two frames: face-to-face, back-to-back, facing toward or away from the participants, facing leftward or rightward from the participants’ perspective, and the empty frames condition without human confederates. There were seven aperture-width conditions—50, 55, 60, 65, 70, 75, and 80 cm—and participants walked at their normal speed through the apertures. We found that the participants’ shoulder rotation angle in the face-to-face condition was significantly greater than that in the empty frames condition. Further, the participants preferred to rotate their shoulders counterclockwise when our confederates in the aperture faced leftward, and clockwise, when they faced rightward. These results suggest that people change their passing-through methods by considering the social nature of the aperture as well as its width.

Sensory substitution: The affordance of passability, body-scaled perception, and exploratory movements

The theory of affordances states that perception is of environmental properties that are relevant to action-capabilities of perceivers. The present study illustrates how concepts and methodological tools from the theory of affordances may help to advance research in the field of sensory substitution. The sensory substitution device (SSD) that was used consisted of two horizontal rows of 12 coin motors that each vibrated as a function of the distance to the nearest object. Sixty blindfolded participants used the SSD to explore virtual horizontal apertures with different widths. They were asked to judge the passability of the apertures. Participants with narrow shoulders judged narrower apertures as passable than participants with wide shoulders. This difference disappeared when aperture width was scaled to shoulder width, demonstrating that perception was body scaled. The actual aperture width was closely related to aspects of the exploratory movements and to aspects of the vibrotactile stimulation that was obtained with the exploratory movements. This implies that the exploratory movements themselves and the vibrotactile stimulation were both informative about the aperture width, and hence that the perception of passability may have been based on either of them or on a global variable that spans vibrotactile as well as kinaesthetic stimulation. Similar performance was observed for participants who accomplished the 7-trial familiarization phase with or without vision, meaning that practice with vision is not indispensable to learn to use the SSD.

The effects of sport specific training of rugby players on avoidance behaviours during a head-on collision course with an approaching person

Individuals use visual information to plan and adapt movements to dynamically changing environments. This information is used to accurately determine when and where they may come in contact with an object. More specifically, individuals may determine the time prior to contacting an object, known as time-to-contact (TTC). Sport provides a scenario where athletes compete in dynamically changing environments and must interact with opposing players. The effects of sport-specific training on obstacle avoidance is highly controversial and research suggests the quantifiable differences in behaviours compared to non-athletes is highly context specific. The current study aimed to examine if sport-specific training has an impact on the avoidance behaviours of rugby players during a head-on collision course with an approaching person. Female rugby players (N = 10, x- = 20 ± 0.94 years) and non-athletes (N = 10, x- = 21.9 ± 1.6 years) were instructed to walk along a 10 m path towards a goal located along the midline. A female confederate initially positioned along the midline 180° from the participant walked towards the participant to one of four predetermined final positions: 1) along the midline in the participants' starting position; 2) stopped along the midline 2.5 m from her starting position; 3) to the left of the participants' starting position; and 4) to the right of the participants' starting position. Results revealed when the path of the confederate was uncertain, individuals used a consistent TTC to determine when to change their path. The rugby players in the current study were found to avoid significantly later (i.e. smaller TTC) than non-athletes. However, following a change in path, sport-specific training did not impact the avoidance behaviours of the groups, but rather the environment was the regulating factor. When the path of the confederate was uncertain, individuals did not use a single avoidance strategy, instead considered the fit between their individual characteristics (i.e., action capabilities) and components of the environment (i.e. path of the confederate and task constraints). Athletes who are specifically trained to pass through spaces and avoid obstacles (i.e., rugby backs) may consider their action capabilities in conjunction with their visual information to determine time of avoidance.

Avoidance behaviours of young adults during a head-on collision course with an approaching person

Individuals use visual information to guide their avoidance behaviours. More specifically, individuals may directly perceive the time prior to colliding with an approaching obstacle (i.e., time to contact, TTC) to determine when to avoid. In addition, individuals use body-scaled information to control their movements. These avoidance behaviours differ when avoiding a human obstacle compared to an inanimate object. As such, the purpose of this experiment was to examine the avoidance behaviours of individuals during a head-on collision course with an approaching person. Young adults (N = 20, [Formula: see text] = 22.25 ± 1.5 years, 10 males) were instructed to walk along a 10 m path towards a goal located along the midline. A female confederate positioned along the midline walked towards the participants to one of the four predetermined final positions: (1) along the midline in the participants' starting position; (2) stopped along the midline 2.5 m from her starting position; (3) to the left of the participants' starting position; and (4) to the right of the participants' starting position. Results revealed when the path of the confederate was certain, individuals used a greater TTC to determine when to change their path in comparison with when the path of the confederate was uncertain. Males were found to avoid significantly earlier (i.e., larger TTC) than females. However, following a change in path, sex did not impact the avoidance behaviours of the groups, but rather, the environment was the regulating factor.

The Effects of Obstacle Type and Locomotion Form on Path Selection in Rugby Players

The current study investigated whether path selection of athletes specifically trained to fit through gaps is affected by the location of human obstacle and the form of locomotion. Female rugby players were instructed to walk, walk with the ball, or run with the ball along a path toward a goal while avoiding three obstacles (three vertical poles or two vertical poles and a confederate) placed halfway along the path, creating two equal apertures of 80 cm. Regardless of the form of locomotion, rugby players chose paths furthest from the confederate, suggesting that confederate location affects path selection. Furthermore, medial-lateral spatial requirements were more variable when participants were walking without the ball than while moving with the ball. Avoidance behaviors, but not path selection, appear to be impacted and minimized during sport-specific movements.

Rate of recalibration to changing affordances for squeezing through doorways reveals the role of feedback

Recalibration of affordance perception in response to changing motor abilities can only occur if observers detect appropriate perceptual information. Recent work suggests that although many affordances can be recalibrated without practicing the specific action to gather outcome feedback-information about whether the attempted action succeeded or failed-calibration of other affordances might depend on outcome feedback (Franchak, Attent Percept Psychophys 79:1816-1829, 2017). However, past work could not rule out the possibility that practicing the action produced perceptual-motor feedback besides outcome feedback that facilitated recalibration. The results of two experiments support the hypothesis that recalibration in a doorway squeezing task depends on outcome feedback as opposed to perceptual-motor feedback. After putting on a backpack that changed participants' doorway squeezing ability, affordance judgments were uncalibrated and remained so even after making repeated judgments. However, after practicing the action, which produced outcome feedback, judgments rapidly calibrated. Moreover, the order of feedback information directly impacted participants' judgments: Participants did not recalibrate if they received only success experience or only failure experience. Recalibration only occurred after participants received both types of feedback experiences, suggesting that outcome feedback is necessary for recalibration in the doorway squeezing task. More generally, the results of the current study support a key tenet of ecological psychology-that affordance perception depends on action-specific information about body-environment relations.

Exploratory behaviors and recalibration: What processes are shared between functionally similar affordances?

Recalibration of affordance perception allows observers to adapt to changes in the body's size or abilities that alter possibilities for action. Of key interest is understanding how exploratory behaviors lead to successful recalibration. The present study was designed to test a novel hypothesis-that the same processes of exploration and recalibration should generalize between affordances that share a similar function. Most affordances for fitting the body through openings are recalibrated without feedback from practicing the action; locomotion exploration is sufficient. The present study used a different fitting task, squeezing through doorways, to determine whether locomotor experience was sufficient for recalibrating to changes in body size that altered affordances. Participants were unable to recalibrate from locomotor experience, demonstrating that exploratory behaviors do not necessarily generalize between functionally similar affordances. Participants only recalibrated following action practice or after receiving feedback about judgment accuracy, suggesting that the informational requirements of the squeezing task may differ from those of other fitting tasks. Implications for affordance theory are discussed.

Designing Smart Objects to Support Affording Situations: Exploiting Affordance Through an Understanding of Forms of Engagement

In this paper I consider how the concept of “affordance” has been adapted from the original writings of Gibson and applied to interaction design. I argue that a clear understanding of affordance shifts the goal of interaction design from one of solely focusing on either the physical object or the capabilities of the person, toward an understanding of interactivity. To do this, I develop the concept of Forms of Engagement, originally proposed to account for tool use. Finally, I extend this concept to interacting with modified tangible user interfaces, or “animate objects.” These animate objects not only sense how they are being used, but also communicate with each other to develop a shared intent, and provide prompts and cues to encourage specific actions. In this way, the human-object-environment system creates affording situations in pursuit of shared intentions and goals. In order to determine when to provide prompts and cues, the objects need to have a model of how they ought to be used and what intention they are being used to achieve. Consequently, affordances become not only the means by which actions are encouraged but also the manner in which intentions are identified and agreed.

Walking through Apertures in Individuals with Stroke

Objective

Walking through a narrow aperture requires unique postural configurations, i.e., body rotation in the yaw dimension. Stroke individuals may have difficulty performing the body rotations due to motor paralysis on one side of their body. The present study was therefore designed to investigate how successfully such individuals walk through apertures and how they perform body rotation behavior.

Method

Stroke fallers (n = 10), stroke non-fallers (n = 13), and healthy controls (n = 23) participated. In the main task, participants walked for 4 m and passed through apertures of various widths (0.9–1.3 times the participant’s shoulder width). Accidental contact with the frame of an aperture and kinematic characteristics at the moment of aperture crossing were measured. Participants also performed a perceptual judgment task to measure the accuracy of their perceived aperture passability.

Results and Discussion

Stroke fallers made frequent contacts on their paretic side; however, the contacts were not frequent when they penetrated apertures from their paretic side. Stroke fallers and non-fallers rotated their body with multiple steps, rather than a single step, to deal with their motor paralysis. Although the minimum passable width was greater for stroke fallers, the body rotation angle was comparable among groups. This suggests that frequent contact in stroke fallers was due to insufficient body rotation. The fact that there was no significant group difference in the perceived aperture passability suggested that contact occurred mainly due to locomotor factors rather than perceptual factors. Two possible explanations (availability of vision and/or attention) were provided as to why accidental contact on the paretic side did not occur frequently when stroke fallers penetrated the apertures from their paretic side.

Perceiving nested affordances for another person's actions

Affordances are available behaviors that emerge out of relations between properties of animals and properties of their environment. Affordances are nested within one another. One way to conceptualize this nesting is through a mean-ends hierarchy. Previous research has shown that perceivers are sensitive to hierarchical means-ends relationships when perceiving affordances for their own actions. Affordances are also nested in a social context. We investigated perception of hierarchical mean-ends nesting of affordances for another person's actions. We asked participants to judge the maximum reaching height of another person (the "actor"). Judgments of the actor's maximum reaching height reflected manipulated constraints on the reaching task, suggesting that participants were sensitive (prospectively) to hierarchical relations between lower order affordances and higher order affordances. In addition, the results revealed that judgments scaled to the reaching ability of the actor and not that of the perceiver. We argue that perceivers were sensitive to hierarchical means-ends nesting of affordances for another person across two-levels of this hierarchy, and that perceivers' judgments were based upon perceptual information about the actor's action capabilities, rather than being based upon simulation of perceivers' own abilities.

The Independent Perceptual Calibration of Action-Neutral and -Referential Environmental Properties

Two experiments were conducted to explore how the calibration of perception of environmental properties taken with reference to an animal and their action capabilities (e.g., affordances) and those that are independent of action capabilities (e.g., metric properties) relate. In both experiments, participants provided reports of the maximum height they could reach above their head with a number of different stick(s) (reach-with-stick height) and the length of those stick(s), a property that is a constituent of reach-with-stick height. In Experiment 1 reach-with-stick height reports improved over trials whereas stick length reports remained constant. In Experiment 2, feedback about maximum reach-with-stick height improved perception of this affordance, but such improvements did not transfer to perception of stick length in a pretest/practice task/posttest design. The results suggest that the perceptual calibration with practice perceiving or feedback about actual dimensions of action-referential and action-neutral properties do not necessarily depend on one another.

The effects of obstacle proximity on aperture crossing behaviours

Affordance theory and behavioural dynamics have been used as theoretical constructs to explain how individuals interact with the environment in order to avoid obstacles. Features of obstacle distance and multiple obstacle avoidance have been discussed in unique studies, yet the interactions of these environmental features have yet to be explored. The purpose of this study was to asses the effects of obstacle distance, relative to the goal, on aperture crossing strategies. Kinematics and gaze behaviours were assessed in a cohort of female young adults (N = 24, 21.3 ± 1.4 years). Results identified that participants chose to navigate through gaps of 1.3× shoulder width or greater, regardless of obstacle distance. However, safety margin in the anterior-posterior direction was found to increase with increased obstacle distance, suggesting unique environmental affordances for each obstacle distance. Therefore, although decision making on whether to navigate through, or around, the aperture appears to be unaffected by obstacle location, specific environmental features result in unique kinematic behaviours. Such behaviours fit within, and add merit to, the tenets of both affordance theory and behavioural dynamics.

Dynamic perception of dynamic affordances: walking on a ship at sea

Motion of the surface of the sea (waves, and swell) causes oscillatory motion of ships at sea. Generally, ships are longer than they are wide. One consequence of this structural difference is that oscillatory ship motion typically will be greater in roll (i.e., the ship rolling from side to side) than in pitch (i.e., the bow and stern rising and falling). For persons on ships at sea, affordances for walking on the open deck should be differentially influenced by ship motion in roll and pitch. Specifically, the minimum width of a walkable path should be greater when walking along the ship's short, or athwart axis than when walking along its long, or fore-aft axis. On a ship at sea, we evaluated the effects of walking in different directions (fore-aft vs. athwart) on actual walking performance. We did this by laying out narrow paths on the deck and asking participants (experienced maritime crewmembers) to walk as far as they could while remaining within the lateral path boundaries. As predicted, participants walked farther along the athwart path than along the fore-aft path. Before actual walking, we evaluated participants' judgments of their walking ability in the fore-aft and athwart directions. These judgments mirrored the observed differences in walking performance, and the accuracy of judgments did not differ between the two directions. We conclude that experienced maritime crewmembers were sensitive to affordances for walking in which the relevant properties of the environment were exclusively dynamic.

Perceptual-motor behaviour during a simulated pedestrian crossing

This study used a novel research paradigm to examine gait control during real-time between-person collision avoidance. Ten young adults (M=20.1±1.52years) were required to walk across a six metre simulated pedestrian crossing, while avoiding a collision with one or two oncoming pedestrians. The potential for social interaction was manipulated by having the oncoming pedestrians walk with (2MP) or without (2P) looking at a mobile phone. Participants took longer to complete the crossing when avoiding a collision with two oncoming pedestrians (2MP: M=5.68s; 2P: M=5.74s) in comparison with baseline (M=4.96s). Gait velocity decreased and was more variable when avoiding a collision during the 2P condition, whilst the anterior-posterior separation distance between pedestrians and the participants at the initiation of peak mediolateral deviation was significantly smaller in 2MP compared to 2P. These findings offer preliminary understanding on how gait control may be adapted to changes in the availability of other persons' gaze orientation information. Future work is needed to further understand how different adaptive behaviours emerge relative to other persons during pedestrian crossings.

Does Visual Performance Influence Head Impact Severity Among High School Football Athletes?

OBJECTIVE

To compare the odds of sustaining moderate and severe head impacts, rather than mild, between high school football players with high and low visual performance.

DESIGN

Prospective quasi-experimental.

SETTING

Clinical Research Center/On-field.

PARTICIPANTS

Thirty-seven high school varsity football players.

INTERVENTIONS

Athletes completed the Nike SPARQ Sensory Station visual assessment before the season. Head impact biomechanics were captured at all practices and games using the Head Impact Telemetry System.

MAIN OUTCOME MEASURES

Each player was classified as either a high or low performer using a median split for each of the following visual performance measures: visual clarity, contrast sensitivity, depth perception, near-far quickness, target capture, perception span, eye-hand coordination, go/no go, and reaction time. We computed the odds of sustaining moderate and severe head impacts against the reference odds of sustaining mild head impacts across groups of high and low performers for each of the visual performance measures.

RESULTS

Players with better near-far quickness had increased odds of sustaining moderate [odds ratios (ORs), 1.27; 95% confidence intervals (CIs), 1.04-1.56] and severe head impacts (OR, 1.45; 95% CI, 1.05-2.01) as measured by Head Impact Technology severity profile. High and low performers were at equal odds on all other measures.

CONCLUSIONS

Better visual performance did not reduce the odds of sustaining higher magnitude head impacts. Visual performance may play less of a role than expected for protecting against higher magnitude head impacts among high school football players. Further research is needed to determine whether visual performance influences concussion risk.

CLINICAL RELEVANCE

Based on our results, we do not recommend using visual training programs at the high school level for the purpose of reducing the odds of sustaining higher magnitude head impacts.

Perception of maximum stepping and leaping distance: Stepping affordances as a special case of leaping affordances

Successfully performing everyday behaviors requires perceiving affordances-possibilities for behavior that depend on the fit between environmental properties and action capabilities. Whereas affordances for some behaviors are primarily constrained by relatively static geometric properties of the perceiver (non-launching behaviors such as stepping), others are additionally constrained by dynamic force production capabilities of the perceiver (launching behaviors such as leaping). This experiment used a transfer of calibration paradigm to investigate whether visual perception of launching and non-launching behaviors represent independent perception-action tasks. In particular, we investigated whether calibration of visual perception of maximum leaping distance transferred to visual perception of maximum stepping distance, and/or vice versa. The results showed that calibration of perception of maximum leaping distance transferred to perception of maximum stepping distance, suggesting that perception of launching and non-launching are not independent. Rather, perception of stepping affordances may be a special case of perception of leaping affordances.

The effects of narrow and elevated path walking on aperture crossing

The study investigated the impact that action capabilities have on identifying possibilities for action, particularly how postural threat influences the passability of apertures. To do this, the ability to maintain balance was challenged by manipulating the level of postural threat while walking. First, participants walked along a 7m path and passed through two vertical obstacles spaced 1.1-1.5×the shoulder width apart during normal walking. Next, postural threat was manipulated by having participants complete the task either walking on a narrow, ground level path or on an elevated/narrow path. Despite a decrease in walking speed as well as an increase in trunk sway in both the narrow and elevated/narrow walking conditions, the passability of apertures was only affected when the consequence of instability was greatest. In the elevated/narrow walking condition, individuals maintained a larger critical point (rotated their shoulders for larger aperture widths) compared to normal walking. However, this effect was not observed for the narrow path walking suggesting that the level of postural threat was not enough to impose similar changes to the critical point. Therefore, it appears that manipulating action capabilities by increasing postural threat does indeed influence aperture crossing behavior, however the consequence associated with instability must be high before both gait characteristics and the critical point are affected.

An enhanced experimental procedure to rationalize on the impairment of perception of action capabilities

It is well documented that changes in the physiological states of the perceiver-actor influence the perception of action capabilities. However, because experimental procedures of most studies involved a limitless availability for stimuli visual encoding and perceptual strategies, it remains difficult to adopt a single position among the large range of alternative interpretations for impaired perception. A reaching-to-grasp paradigm under breathing restriction was adapted from Graydon et al. (Cogn Emot 26:1301-1305, 2012) to standardize the time for encoding of stimuli information and narrowed the involvement of perceptual strategies. In the present study, we propose a highly controlled environment where the discrete information is presented during 300 ms, congruently with neurophysiological studies focused on visuomotor transformation. An underestimation of the perception of action capabilities is found under breath restriction, suggesting that 300 ms for stimuli encoding is sufficient to induce altered visuomotor brain transformations when limiting the involvement of perceptual strategies. This result suggests that such behavior could refer to an impaired brain potentiation of the perceptual occurrence, providing strong hypotheses on the brain dynamics of sensorimotor integration that underlie impaired perception of action capabilities in stressful situations.

The effects of specific athletic training on path selection while running

Apertures that are smaller than 1.3 times the shoulder width (SW) require that individuals make an adjustment to their normal walking behavior [6]. When given a choice, individuals will choose to avoid apertures smaller than this ratio, rather than rotate their shoulders and walk through [7]. Research has yet to determine whether this choice in path selection can be influenced by the speed at which one approaches the aperture or by experience/training. Therefore, the current study investigated whether approach speed and/or specific athletic training influences the choice in path selection. Specifically-trained athletes (n=6) and non-trained (n=6) young adults ran toward a visible goal placed at the end of the path and avoided an aperture (created by two poles) placed along the midline of the path. The separation between the poles ranged between 0.6 and 1.8 times each participant's SW, in increments of 0.2. Participants were permitted to either run through or around the aperture to get to the end goal. Results demonstrated that regardless of training experience, participants ran around apertures smaller than 1.4× the SW and ran through apertures larger than this ratio. Increased approach speed (i.e., running) therefore appears to elicit similar aperture crossing behaviors as walking [2,3,6,7]. Additionally, when faced with the choice to run around or to run through apertures, individuals who are specifically-training to run through small spaces chose similar paths as individuals who are not trained to do so. Therefore, specific training does not appear to influence voluntary path selection.

Visuomotor deficits during locomotion in previously concussed athletes 30 or more days following return to play

Current protocols for returning athletes to play (RTP) center around resolution of physical symptoms of concussion. However, recent research has identified that balance and cognitive deficits persist beyond physical symptom recovery. Protocols that involve testing dynamic balance and visuomotor integration have been recommended as potential tools for better understanding of length of impairment following concussion. A dynamic, visuomotor paradigm was undertaken in the current study to assess decision making in athletes who had sustained a concussion >30 days before study participation and had been cleared to RTP (N = 10). Two obstacles created a gap that varied between 0.6 and 1.8× participants' individual shoulder width in open space. Participants made decisions to navigate through or deviate around the gap created by the two obstacles. The results revealed that previously concussed athletes were highly variable in their decision making and demonstrated variable Medial‐Lateral (ML) center of mass (COM) control when approaching the obstacles, when compared with nonconcussed, age‐matched controls. As such, they showed poor visuomotor control and decision making, as well as poor dynamic stability compared to controls. Visuomotor deficits were persistent in the sample of previously concussed individuals, well beyond deficits identified by current RTP standards. This study suggests that dynamic, visuomotor integration tasks may be of benefit to increase rigor in RTP protocols and increase safety of athletes returning to sport.

Cognitive recovery from concussion does not coincide with physical symptom recovery. Deficits of concussion persist well beyond the believed 30 days of recovery. Visuomotor paradigms in combination with balance control can determine concussion recovery.

Gut estimates: Pregnant women adapt to changing possibilities for squeezing through doorways

Possibilities for action depend on the fit between the body and the environment. Perceiving what actions are possible is challenging, because the body and the environment are always changing. How do people adapt to changes in body size and compression? In Experiment 1, we tested pregnant women monthly over the course of pregnancy to determine whether they adapted to changing possibilities for squeezing through doorways. As women gained belly girth and weight, previously passable doorways were no longer passable, but women's decisions to attempt passage tracked their changing abilities. Moreover, their accuracy was equivalent to that of nonpregnant adults. In Experiment 2, nonpregnant adults wore a "pregnancy pack" that instantly increased the size of their bellies, and they judged whether doorways were passable. Accuracy in the "pregnant" participants was only marginally worse than that of actual pregnant women, suggesting that participants adapted to the prosthesis during the test session. In Experiment 3, participants wore the pregnancy pack and gauged passability before and after attempting passage. The judgments were grossly inaccurate prior to receiving feedback. These findings indicate that experience facilitates perceptual-motor recalibration for certain types of actions.

Affordances as Probabilistic Functions: Implications for Development, Perception, and Decisions for Action

We propose a new way to describe affordances for action. Previous characterizations of affordances treat action possibilities as binary categories-either possible or impossible-separated by a critical point. Here, we show that affordances are probabilistic functions, thus accounting for variability in motor performance. By measuring an affordance function, researchers can describe the likelihood of success for every unit of the environment. We demonstrate how to fit an affordance function to performance data using established psychophysical procedures and illustrate how the threshold and variability parameters describe different possibilities for action. Finally, we discuss the implications of probabilistic affordances for development, perception, and decision-making.