A common perceptual parameter for stair climbing for children, young and old adults

Affordances for throwing: An uncontrolled manifold analysis

Movement systems are massively redundant, and there are always multiple movement solutions to any task demand; motor abundance. Movement consequently exhibits 'repetition without repetition', where movement outcomes are preserved but the kinematic details of the movement vary across repetitions. The uncontrolled manifold (UCM) concept is one of several methods that analyses movement variability with respect to task goals, to quantify repetition without repetition and test hypotheses about the control architecture producing a given abundant response to a task demand. However, like all these methods, UCM is under-constrained in how it decomposes a task and performance. In this paper, we propose and test a theoretical framework for constraining UCM analysis, specifically the perception of task-dynamical affordances. Participants threw tennis balls to hit a target set at 5m, 10m or 15m, and we performed UCM analysis on the shoulder-elbow-wrist joint angles with respect to variables derived from an affordance analysis of this task as well as more typical biomechanical variables. The affordance-based UCM analysis performed well, although data also showed thrower dynamics (effectivities) need to be accounted for as well. We discuss how the theoretical framework of affordances and affordance-based control can be connected to motor abundance methods in the future.

How the conception of control influences our understanding of actions

Wilful movement requires neural control. Commonly, neural computations are thought to generate motor commands that bring the musculoskeletal system - that is, the plant - from its current physical state into a desired physical state. The current state can be estimated from past motor commands and from sensory information. Modelling movement on the basis of this concept of plant control strives to explain behaviour by identifying the computational principles for control signals that can reproduce the observed features of movements. From an alternative perspective, movements emerge in a dynamically coupled agent-environment system from the pursuit of subjective perceptual goals. Modelling movement on the basis of this concept of perceptual control aims to identify the controlled percepts and their coupling rules that can give rise to the observed characteristics of behaviour. In this Perspective, we discuss a broad spectrum of approaches to modelling human motor control and their notions of control signals, internal models, handling of sensory feedback delays and learning. We focus on the influence that the plant control and the perceptual control perspective may have on decisions when modelling empirical data, which may in turn shape our understanding of actions.

Knee Extensor Muscle Strength Is More Important Than Postural Balance for Stair-Climbing Ability in Elderly Patients with Severe Knee Osteoarthritis

Knee osteoarthritis is a chronic joint disease which damages articular cartilage. In its severe stages, it results in impairments in balance and muscle strength loss, which affect daily life activities such as walking or climbing stairs. This study sought to investigate associated factors with stair-climbing ability in this population, with special interest in measuring the relevance of postural balance for this task. Forty-four patients scheduled to undergo unilateral total knee arthroplasty were assessed. Timed up and go test, stair ascent–descent test, three different isometric strength tests (knee flexion, knee extension and hip abduction), active knee extension and flexion range of movement and static postural balance assessment were evaluated. Spearman’s correlation coefficients and multiple linear regression analysis determined the strength of association between the different variables and stair-climbing time. No significant association between the stair-climbing time and static balance was found. Significant associations were found between stair-climbing time and timed up and go (r = 0.71; p < 0.0001) and maximal knee extensor strength (r = –0.52; p = 0.0003). One-year increase in age was associated with 0.15 s (95% CI 0.00 to 0.30) slower stair-climbing time. In conclusion, muscle strength is more important than postural balance for stair-climbing ability in this population.

Developmental differences across the lifespan in the use of perceptual information to guide action-based decisions

Perceptual information about unfolding events is important for guiding decisions about when and how to move in real-world action situations. As an exemplary case, road-crossing is a perceptual-motor task where age has been shown to be a strong predictor of risk due to errors in action-based decisions. The present study investigated age differences between three age groups (Children: 10-12 years old; Adults: 19-39 years old; Older Adults: 65 + year olds) in the use of perceptual information for selection, timing, and control of action when crossing a two-way street in an immersive, interactive virtual reality environment. Adults and children selected gaps to cross that were consistent with the use of a time-based information variable (tau), whereas older adults tuned less into the time-based variable (tau) to guide road-crossing decisions. For action initiation and control, children and adults also showed a strong ability to precisely time their entry with respect to the lead vehicle maximising the available time to cross and coordinating walking movements with the tail vehicle to ensure they were not on a collision course. In contrast, older adults delayed action initiation and showed difficulty coordinating self-movement with the approaching vehicle. This study and its results tie together age-based differences in the three components of action decision-making (selection, timing and control) within a unified framework based on perceptual information. The implications of these age-related differences in action decisions and crossing behaviours are discussed in the context of road safety.

Does it still fit? - Adapting affordance judgments to altered body properties in young and older adults

Actor-related affordance judgments are decisions about potential actions that arise from environmental as well as bodily and cognitive conditions. The system can be challenged by sudden changes to otherwise rather stable actor references e.g. due to accidental bodily injuries or due to brain damage and resulting motor and cognitive constraints. The current study investigated adaptation to suddenly artificially altered body properties and its reversibility in healthy young versus older adults. Participants were asked to judge whether they would be able to fit their hand through a given horizontal opening (Aperture Task). Body alterations were induced by equipping participants with one hand splint for 24 hours that enlarged the hand in width and height. Participants were tested before and directly after putting the splint on as well as after a habituation period of 24 hours. To assess reversibility, participants were tested again directly after removing the splint and one day later. Judgment accuracy values and detection theory measures were reported. Both, young and older adults judged more conservatively when body properties were altered compared to initial judgments for normal body properties. Especially older adults showed major difficulties in such quick adaptation. Older adults' judgment accuracy as well as perceptual sensitivity were significantly lowered when body properties were suddenly altered. Importantly, lowered judgment performance occurred for both, the splinted as well as the non-splinted hand in older adults. Only after 24 hours of habituation, older adults tended to regain initial performance levels showing adaptive behavior to the altered condition. Removing the hand splint for one day was sufficient to reverse these adaptive effects. Our study results suggest that aging slows down adaptation to sudden bodily alterations affecting actor-related affordance judgments. We propose that these altered processes may go along with uncertainty and a heightened concern about potential consequences of misjudgments. Clearly, future studies are needed to further elucidate the underlying processes of adaptation in affordance judgments. These may reveal major implications for the aging society and its associated problems with an increased risk of falling or stroke related bodily constraints.

Reliability and construct validity of the stepping-forward affordance perception test for fall risk assessment in community-dwelling older adults

Thus far, few studies have examined the estimation and actual performance of locomotor ability in older adults. To our knowledge, there are no studies examining the relationship between stepping-forward estimation versus ability and fall occurrence. The aim of this study was to develop and assess the reliability and validity of a new test for fall risk assessment in community-dwelling older adults. In total, 347 participants (73.1 ± 6.2 years; 266 women) were assessed for their perception of maximum distance for the stepping-forward and action boundary. The test was developed following the existing literature and expert opinions. The task showed strong internal consistency. Intraclass correlation ranged from 0.99 to 1 for intrarater agreement and from 0.83 to 0.97 for interrater agreement. Multivariate binary regression analysis models revealed an area under the curve (AUC) of 0.665 (95% CI: 0.608–0.723) for fallers and 0.728 (95% CI: 0.655–0.797) for recurrent fallers. The stepping-forward affordance perception test (SF-APT) was demonstrated to be accurate, reliable and valid for fall risk assessment. The results showed that a large estimated stepping-forward associated with an underestimated absolute error works as a protective mechanism for fallers and recurrent fallers in community-dwelling older adults. SF-APT is safe, quick, easy to administer, well accepted and reproducible for application in community or clinical settings by either clinical or nonclinical care professionals.

Mind the Gap: Gap Affordance Judgments of Children, Teens, and Adults in an Immersive Virtual Environment

Affordances are possibilities for action that depend on both an observer's capabilities and the properties of the environment. Immersive Virtual Environments (IVEs) have been used to examine affordances in adults, demonstrating that judgments about action capabilities are made similarly to the real world. However, less is known about affordance judgments in middle-aged children and adolescents in IVEs. Differences in rate of growth, decision criteria, and perceived risk could influence affordance judgments for children. In Experiment 1, children, teens, and adults stood in an IVE at ground level or at a height of 15 m, and were asked to view gaps of different widths. Across all age groups, estimates of gap crossing were underestimated at the higher height compared to the ground, consistent with reports of fear and risk of falling. Children, compared to adults, underestimated their maximum crossable gap compared to their actual crossable gap. To test whether this difference was specific to IVEs or a more generalized age effect, children and adults were tested on gap estimates in the real world in Experiment 2. This real world study showed no difference between children and adults, suggesting a unique contribution of the IVE to children's affordance judgments. We discuss the implications for using IVEs to study children's affordances.

The Critical Point to Step into a Hole is Similar in Young and Older Adults

The avoidance of a hole in the pathway while walking has been systematically investigated; however, depending on the dimensions of the hole, the option to avoid it is infeasible, and it is necessary to use the so-called accommodation strategy to step into the hole. We investigated the critical point between the avoidance and accommodation strategies when dealing with a hole in the ground during locomotion of young and older adults. Young and older adults performed two tasks: verbal estimation and walking. We used holes of different lengths and constant depth (12 cm). In the verbal estimation task, participants stood and looked at each hole and verbally respond if they would step into or avoid it. In the walking task, they walked and chose to either step or avoid the hole. Both age groups preferred to step into the hole when it was larger than 1.3 times their foot length in both tasks. The perception of affordances of young and older adults to step into a hole was similar, and it was unaffected by the investigated tasks. Thus, our participants preferred to have a safety margin that was large enough to guarantee that the whole foot would accommodate within the hole.

Age-related differences in the perception of gap affordances: Impact of standardized action capabilities on road-crossing judgements

Recent road-crossing literature has found that older adults show performance differences between estimation and perception-action tasks suggesting an age-related difficulty in accurately calibrating the information picked up from the surrounding environment to their action capabilities (Lobjois and Cavallo, 2009). The present study investigated whether participants could accurately perceive gap affordances via information that specifies the time-to-arrival of the approaching cars. To ensure the opportunities for action were the same across different age groups, independent of the actor's action capabilities, the action of crossing the road was standardised. A total of 45 participants (15 children, aged 10-12, 15 adults aged 19-39, 15 older adults aged 65+) were asked to judge, by pressing a button in a head-mounted display, whether the gap between oncoming cars afforded crossing. When the participant pressed the button, they moved across the road at a fixed speed. Adherence to a time-based variable (namely tau) explained 85% and 84% of the variance in both the children and adults' choices, respectively. Older adults tuned less into the time-based variable (tau) with it only accounting for 59% of the variance in road-crossing decisions. These findings suggest that, the ability to use tau information which specifies whether a gap affords crossing or not, deteriorates with age.

Does it fit? - Trainability of affordance judgments in young and older adults

Will I fit into the overcrowded subway? Advanced aging can change our abilities associated with accurately judging the fit between perceived environmental properties and our own actual physical capabilities (affordance judgments). Two experimental studies examined the effects of aging and trainability in affordance judgments. Participants were asked to decide whether their hand fits into a given opening (Aperture Task). We used a detection theory approach to evaluate different judgment characteristics. Study 1 demonstrated that older (N = 39) compared to younger adults (N = 39) produced rather conservative judgments, but did not differ in perceptual sensitivity. Distributions of Hit and False-Alarm rates, as well as risk-perception statements (DOSPERT questionnaire), indicated a heightened concern about potential consequences of misjudgments in older adults. In Study 2, 20 younger and 22 older adults were trained by actually trying to fit their hand into each presented opening. Training included acoustic, haptic and visual feedback. Compared to pre-training, both groups demonstrated significant increases in accuracy when assessed post-training and after a one-week follow-up. While younger adults improved in perceptual sensitivity in post-training as well as in follow-up, the older group adjusted their tendency towards less conservative judgments in both following sessions. Our results are consistent with affordance models that propose a complex and dynamic interplay of different neural processes involved in this skill. Future studies are needed to further elucidate that interplay and the trainability of affordance judgments.

Affordance Realization in Climbing: Learning and Transfer

The aim of this study was to investigate how the affordances of an indoor climbing wall changed for intermediate climbers following a period of practice during which hold orientation was manipulated within a learning and transfer protocol. The learning protocol consisted of four sessions, in which eight climbers randomly ascended three different routes of fixed absolute difficulty (5c on the French scale), as fluently as possible. All three routes were 10.3 m in height and composed of 20 hand-holds at the same locations on an artificial climbing wall; only hold orientations were altered: (i) a horizontal-edge route (H) was designed to afford horizontal hold grasping, (ii) a vertical-edge route (V) afforded vertical hold grasping, and (iii), a double-edge route (D) was designed to afford both horizontal and vertical hold grasping. Five inertial measurement units (IMU) (3D accelerometer, 3D gyroscope, 3D magnetometer) were attached to the hip, feet and forearms to analyze the vertical acceleration and direction (3D unitary vector) of each limb and hip in ambient space during the entire ascent. Segmentation and classification processes supported detection of movement and stationary phases for each IMU. Depending on whether limbs and/or hip were moving, a decision tree distinguished four states of behavior: stationary (absence of limb and hip motion), hold exploration (absence of hip motion but at least one limb in motion), hip movement (hip in motion but absence of limb motion) and global motion (hip in motion and at least one limb in motion). Results showed that with practice, the learners decreased the relative duration of hold exploration, suggesting that they improved affordance perception of hold grasp-ability. The number of performatory movements also decreased as performance increased during learning sessions, confirming that participants' climbing efficacy improved as a function of practice. Last, the results were more marked for the H route, while the D route led to longer relative stationary duration and a shorter relative duration of performatory states. Together, these findings emphasized the benefit of manipulating task constraints to promote safe exploration during learning, which is particularly relevant in extreme sports involving climbing tasks.

Schizophrenia: An Impairment in the Capacity to Perceive Affordances

Phenomenological psychopathologists conceptualize schizophrenia as a self-disorder involving profound distortions of selfhood. For James Gibson, “to perceive the world is to coperceive oneself.” If the sense of self is disturbed in individuals with schizophrenia, this could also lead to disturbances in these individuals’ ability to perceive affordances, environmental properties taken with reference to the perceiver’s action capabilities (e.g., a rigid surface affording ‘walk-on-able,’ chairs ‘sit-on-able,’ and so on). To test this hypothesis, three experiments investigated schizophrenia patients’ affordance perception. Participants were presented with a photo of a common object on the computer and then asked to judge its secondary affordance (a non-designed function) in a two-choice reaction time task in Experiment 1 and in a yes/no task in Experiment 2. Schizophrenia participants performed less accurately and more slowly than controls. To rule out visual impairment as a contributing factor, in Experiment 3, participants identified physical properties (color, shape, material composition) of the objects. Schizophrenia participants were as accurate as controls and responded faster than in the previous experiments. Results suggest that the capacity to perceive affordances is likely impaired in people with schizophrenia, although the capacity to detect the object’s physical properties is kept intact. Inability to perceive affordances, those functionally significant properties of the surrounding environment, may help explain why schizophrenia patients may appear as somewhat detached from the world.

Falls, muscle strength, and functional abilities in community-dwelling elderly women

Abstract Introduction: Falls are among the most common and serious problems facing elderly women. Falling is associated with increased mortality, morbidity, reduced functioning, loss of independence and hospitalization. Objective: The aim of this study was to investigate the association among fear of falling, muscle strength, and functional abilities in community-dwelling elderly women. Methods: Forty-nine elderly women (70.57 ± 5.59 years) participated in this study. Records of falls, self-efficacy associated with falls (FES-I Brazil), functional abilities (the Timed Up and Down Stairs test [TUDS] and the Timed Up and Go test [TUG]), lower limb muscle strength (knee extensors and ankle plantar flexors), and hand grip strength were investigated as variables of interest. Descriptive statistics, the one-way ANOVA, and linear regression tests were used to analyze the association between fear of falling and falls with other variables (α = 0.05). Results: Elderly women who presented records of falls within the last year had lesser strength of knee extensors and plantar flexors (p ≤. 05). Those who had low self-efficacy associated with falls presented lower strength of knee extensors (p ≤. 01). Variables associated with functional abilities (r = 0.70) and lower limb strength (r = 0.53) showed a positive correlation (p ≤. 01). Conclusion: The concern with the fear of falling and falls may be negative effects caused by lower limb muscle weakness.

Towards an ecologically grounded functional practice in rehabilitation

According to the International Classification of Functioning, Disability and Health, effective rehabilitation requires interventions that go beyond minimizing pathological conditions and associated symptoms. The scope of practice must include promoting an individual's activity within relevant contexts. We argue that best practice requires decisions that are not only evidence-based but also theory-based. Perception and action theories are essential for interpreting evidence and clinical phenomena as well as for developing new interventions. It is our contention that rehabilitation goals can best be achieved if inspired by the ecological approach to perception and action, an approach that focuses on the dynamics of interacting constraints of performer, task and environment. This contrasts with organism-limited motor control theories that have important influence in clinical practice. Parallels between such theories and the medical model of care highlight their fundamental inconsistency with the current understanding of functioning. We contend that incorporating ecological principles into rehabilitation research and practice can help advance our understanding of the complexity of action and provide better grounding for the development of effective functional practice. Implications and initial suggestions for an ecologically grounded functional practice are outlined.

MULTI-SEGMENTED TRUNK MOTION OF HEALTHY NON-ELDERLY ADULTS IN DIFFERENT DECADES OF LIFE

Traditionally, gait analysis models the trunk as one rigid body segment. This approach has limitations; it does not capture all the movements of this area of the body throughout locomotion. Lower-extremity-gait kinematics do not routinely change in healthy non-elderly adults in different decades of life; however, it is unknown if trunk kinematics will be altered during different activities of daily living as a function of age. The purpose of this study was to determine if a previously validated multi-segmented trunk model would detect trunk movement variations in non-elderly healthy adults in different decades of life. Thirty-four non-elderly healthy adults in various decades of life (20-29 years, 30-39 years, 40-49 years, and 50-59 years) completed two tasks of ambulatory daily living (level walking and stair descent). Trunk maximum angle during the gait cycle, timing of the trunk maximum angle during the gait cycle and trunk range of motion were examined using analysis of variance procedures. Findings are that age group did not affect the trunk kinematics of individuals in different decades of life, but that may not represent the experiences of elderly individuals.

THREE-DIMENSIONAL MULTI-SEGMENTED SPINE JOINT REACTION FORCES DURING COMMON WORKPLACE PHYSICAL DEMANDS/ACTIVITIES OF DAILY LIVING

Objective

The quantification of inter-segmental spine joint reaction forces during common workplace physical demands.

Background

Many spine reaction force models have focused on the L5/S1 or L4/L5 joints to quantify the vertebral joint reaction forces. However, the L5/S1 or L4/L5 approach neglects most of the intervertebral joints.

Methods

The current study presents a clinically applicable and noninvasive model which calculates the spinal joint reaction forces at six different regions of the spine. Subjects completed four ambulatory activities of daily living: level walking, obstacle crossing, stair ascent, and stair descent.

Results

Peak joint spinal reaction forces were compared between tasks and spine regions. Differences existed in the bodyweight normalized vertical joint reaction forces where the walking (8.05±3.19N/kg) task had significantly smaller peak reaction forces than the stair descent (12.12±1.32N/kg) agreeing with lower extremity data comparing walking and stair descent tasks.

Conclusion

This method appears to be effective in estimating the joint reaction forces using a segmental spine model. The results suggesting the main effect of peak reactions forces in the segmental spine can be influenced by task.

Developmental coordination disorder and its cause: The road less travelled

We critically review the research literature that seeks to focus on the possible cause of children diagnosed with developmental coordination disorder (DCD). In so doing we contrast the traditional information processing (IP) approach as a model to explain the causal factors that account for the motor deficits present in children with DCD, with a dynamical systems (DS) account which argues that coordination deficits in children with DCD is less to do with problems of poor internal models (a cornerstone of IP theory) and more with a degrading of perception-action coupling. We review and comment on the extant empirical data and conclusions of both approaches. We conclude that the data for an IP explanation is weak and a reconsideration of DCD is in order with respect to the underlying cause of this issue.

Body-scaled affordances in sensory substitution

The research field on sensory substitution devices has strong implications for theoretical work on perceptual consciousness. One of these implications concerns the extent to which the devices allow distal attribution. The present study applies a classic empirical approach on the perception of affordances to the field of sensory substitution. The reported experiment considers the perception of the stair-climbing affordance. Participants judged the climbability of steps apprehended through a vibrotactile sensory substitution device. If measured with standard metric units, climbability judgments of tall and short participants differed, but if measured in units of leg length, judgments did not differ. These results are similar to paradigmatic results in regular visual perception. We conclude that our sensory substitution device allows the perception of affordances. More generally, we argue that the theory of affordances may enrich theoretical debates concerning sensory substitution to a larger extent than has hitherto been the case.

Dynamic stability during running gait termination: Differences in strategies between children and adults to control forward momentum

Rapid deceleration during running is key for successful participation in most childhood activities and sports; this requires modulation of body momentum and consequent challenges to postural equilibrium. The purpose of this study was to investigate the strategies employed by adults and children to control forward momentum and terminate running gait. Sixteen young adults and 15 pre-pubertal children completed two tasks as fast as possible: an unobstructed run (RUN) and a run and stop (STOP) at a pre-determined location. For STOP, center of mass (COM) approach velocity and momentum prior to deceleration and spatiotemporal characteristics and COM position during deceleration were compared between groups. Position and velocity variables were normalized to height and maximum velocity during RUN, respectively. Children used fewer steps with relatively longer step length to decelerate over a relatively longer distance and longer time than adults. Children approached at higher relative velocity than adults, but adults approached with greater momentum. Adults positioned their COM lower and more posterior than children throughout deceleration. Our results suggest that pre-pubertal children and young adults employ different strategies to modulate body momentum, with adults exhibiting mechanics characteristic of a more stable strategy. Despite less stable mechanics, children and adults achieved similar success.

Social cognition in simple action coordination: A case for direct perception

In this paper we sketch the outlines of an account of the kind of social cognition involved in simple action coordination that is based on direct social perception (DSP) rather than recursive mindreading. While we recognize the viability of a mindreading-based account such as e.g. Michael Tomasello's, we present an alternative DSP account that (i) explains simple action coordination in a less cognitively demanding manner, (ii) is better able to explain flexibility and strategy-switching in coordination and crucially (iii) allows for formal modeling. This account of action coordination is based on the notion of an agent's field of affordances. Coordination ensues, we argue, when, given a shared intention, the actions of and/or affordances for one agent shape the field of affordances for another agent. This a form of social perception since in particular perceiving affordances for another person involves seeing that person as an agent. It is a form of social perception since it involves perceiving affordances for another person and registering how another person's actions influence one's own perceived field of affordances.

Ledge and wedge: younger and older adults' perception of action possibilities

The current study investigated whether younger (college-age) and older adults (60+ years) differ in their ability to perceive safe and unsafe motor actions. Participants decided whether to walk through openings varying in width in two penalty conditions: In the doorway condition, if participants attempted to squeeze through impossibly narrow openings, the penalty for error was entrapment. In the ledge condition, if participants attempted to inch along impossibly narrow ledges, the penalty for error was falling. Results showed that across the lifespan, people consider falling to be a more severe penalty than getting stuck: Both younger and older adults made more conservative decisions when the penalty for error was falling, and older women were especially leery of falling. In both age groups, abilities and decisions were based on dynamic properties of the body, such as compressed body size in the doorway condition and balance in the ledge condition. Findings indicate that failure to perceive possibilities for action is unlikely to be the cause of the increased prevalence of falling in older adults.

The impact of body-scaled information on reaching

BACKGROUND

Environmental and task modifications are powerful methods used to affect action in rehabilitation and are frequently used by therapists.

OBJECTIVE

The purpose of this study was to examine and quantify the relationship between hand size (person characteristics) and object size (environmental characteristics) and the effect of this relationship on the emergent reaching patterns for children and adults with typical development.

DESIGN

This was a cross-sectional prospective study.

METHODS

Seventeen children and 20 adults participated and were required to reach and grasp 10 pairs of cubes of different sizes. The dimensionless ratios were calculated by dividing the cube size by the aperture between index finger and thumb to quantify emergent reach and grasp patterns. A critical ratio was used to establish the shift from a 1-handed to an exclusive 2-handed reach pattern.

RESULTS

The results demonstrated no significant difference in the mean critical ratios between the 2 groups. However, a 2-handed reach was used more frequently than a 1-handed reach at a significantly smaller ratio for children in comparison with adults.

LIMITATIONS

The relational metrics between the cube and hand are only one contribution to the emergent reaching and grasping patterns.

CONCLUSIONS

Children had more variability of reaching patterns than adults. A personal constraint, such as experience, and a task constraint of accuracy may account for the variability. The results encourage further research on body-scaled information for individuals with different personal constraints (eg, children with cerebral palsy) and the impact of body-scaled information on emergent actions.

Locomotor behaviour of children while navigating through apertures

During everyday locomotion, we encounter a range of obstacles requiring specific motor responses; a narrow aperture which forces us to rotate our shoulders in order to pass through is one example. In adults, the decision to rotate their shoulders is body scaled (Warren and Whang in J Exp Psychol Hum Percept Perform 13:371-383, 1987), and the movement through is temporally and spatially tailored to the aperture size (Higuchi et al. in Exp Brain Res 175:50-59, 2006; Wilmut and Barnett in Hum Mov Sci 29:289-298, 2010). The aim of the current study was to determine how 8-to 10-year-old children make action judgements and movement adaptations while passing through a series of five aperture sizes which were scaled to body size (0.9, 1.1, 1.3, 1.5 and 1.7 times shoulder width). Spatial and temporal characteristics of movement speed and shoulder rotation were collected over the initial approach phase and while crossing the doorway threshold. In terms of making action judgements, results suggest that the decision to rotate the shoulders is not scaled in the same way as adults, with children showing a critical ratio of 1.61. Shoulder angle at the door could be predicted, for larger aperture ratios, by both shoulder angle variability and lateral trunk variability. This finding supports the dynamical scaling model (Snapp-Childs and Bingham in Exp Brain Res 198:527-533, 2009). In terms of movement adaptations, we have shown that children, like adults, spatially and temporally tailor their movements to aperture size.

Effects of load carrying methods and stair slopes on physiological response and postures during stairs ascending and descending

The purpose of this study was to examine the effects of load carrying methods, stair slopes and walking speeds on heart rate and walking postures. Nine participants climbed up and down stairs with various stair slopes (24°, 30° and 36°), walking speeds (72, 96, and 132 steps per minute), and using different load carrying methods (empty loads, backpack, and hand-held). The effects of these factors on heart rate, Borg-RPE and flexion angles of knee joints, hip joints and trunk angles were investigated. This study demonstrated that increased stair slopes and walking speed were associated with increased heart rate and RPE. The heart rate for empty loads subjects was lowest, followed by backpack load and hand-held load. Climbing stairs with larger inclination was associated with smaller knee joint flexion angle and larger trunk and hip joint flexion angle. In conclusion, it is easier for subjects to carry a load of the same weight up stairs by backpack than by hand. However, the stair slope should be less than 30°. Thus, the standard fixed stair slope (30° of stair slope) on recommended for riser height and tread depth are 160 mm (6.5 inches) and tread depth 280 mm (11 inches).

Development of visual control in stepping down

Stepping down at a change of height is a fundamental part of human locomotion. At a novel step, this requires the transformation of visual information about a depth change into a stepping movement of appropriate size. However, little is known about this process or its development. We studied adults, 3- and 4-year-old children stepping down a single stair of variable height. We assessed how well stepping down was scaled to stair height using several kinematic measures. Of these, 'kneedrop' and 'toedrop' describe how far the leg has descended by the time it begins to 'swing in' in preparation for landing; and 'toeheight (speedpeak)' describes where the toe begins to decelerate. If visually controlled, their values should scale to the height of the stair. Under normal visual conditions, children scaled these movements to stair height as well as adults. In a second condition, participants closed their eyes just before stepping down to remove visual feedback during the step. Adults' steps were barely affected. For 4-year olds, only toeheight (speedpeak) decreased. For 3-year olds, both toedrop and toeheight (speedpeak) scaled less well to stair height than normal. The results suggest that visuomotor processes for fine-tuned stepping control develop remarkably early, but are initially dependent on visual feedback.

The affordance of barrier crossing in young children exhibits dynamic, not geometric, similarity

Previous research has shown that adults perceive affordances like the passability of apertures, climbability or crossability of steps and graspability of objects. In this study, the affordance for stepping over or onto barriers was examined in young children. This was done by placing three distinct barriers (a foam obstacle, a gap, and a single step up), which were scaled to body size, in the walking paths of 4- and 6-year olds and adults, and observing how they crossed the barriers. Age-related differences in the scaling of these actions corresponded to levels of movement variability, indicating that children as young as 4 years old are sensitive to their own constraints and scale their actions accordingly. These results indicate that affordances are not directly related to leg geometry, but rather entail the dynamics of the developing perception-action system.

Naturalizing Perception

We believe that one of the most important aspects of Gibson's ecological psychology is his attempted naturalization of perception, that is, his attempt to place perception in the context of evolutionary theory. However, the dominant neo-Gibsonian approach to perception has been criticized for being inconsistent with evolutionary theory. We argue that a central tenet of this approach indeed runs counter to evolutionary considerations. Based on an evolutionary analysis of the use of information, we sketch an alternative development of Gibson's pioneering ideas. A truly naturalistic theory of perception, we argue, should recognize both suboptimalities in perception and variation among the members of a population in what informational variables are used. Like other variable organismal features, the use of information is a function of multiple factors. We will compare this naturalistic ecological approach with both Gibson's own perspective and more recent frameworks.

The effects of aging on street-crossing behavior: from estimation to actual crossing

Based on an interactive road-crossing task, this study examined age-related effects on crossing decisions and whether or not age affects behavioral adjustments to the time gap. It also compared crossing-task decisions to previously observed estimation-task decisions [Lobjois, R., Cavallo, V., 2007. Age-related differences in street-crossing decisions: the effects of vehicle speed and time constraints on gap selection in an estimation task. Accident Analysis and Prevention 39 (5), 934-943]. The results showed that older adults selected a greater mean time gap and initiated their crossing sooner than the younger ones, indicating an attempt to compensate for their increased crossing time. However, older adults accepted shorter and shorter time gaps as speed increased, putting them at a higher risk at high speeds. Regarding adaptive behavior, the analyses showed that all groups adjusted their crossing time to the available time. Comparison of crossing decisions and estimations revealed that the young group had a greater number of tight fits and missed fewer opportunities on the crossing task, whereas these differences did not appear in the elderly. This suggests that the crossing decisions of younger adults are much more finely tuned to time gaps in actual crossing tasks than in estimation tasks and that older adults have trouble calibrating perception and action and perceiving possibilities for action.

Dimensional analysis and ground reaction forces for stair climbing: effects of age and task difficulty

Altered perception-action capability is often associated with falls and diminished self-efficacy in older people. This study evaluated and compared perception-action capability in stair-climbing performance of 18 healthy volunteers assigned to two age groups (mean age, 26.3+/-4.3 years and 66.4+/-4.7 years, respectively). The experimental set-up included 14 stairs (50 cm wide, 60 cm deep, riser height 35-90 cm) positioned at the edge of a force platform. The task was to climb the stair with the greatest riser height subjects thought they could climb without outside support or use of hands. Dimensional and dynamic data were collected and analyzed to reveal the invariant relationships that sustain action preparation and execution. All subjects chose the same proportion between stair height and distance covered before mounting the stair, as expressed by the invariant angle (alpha). While the geometric invariant relationship was picked up as a visual guide prior to action, there was a dynamic invariance in the forces applied during actual execution. To establish whether the invariance still held in extreme cases, two perturbed conditions were introduced in which stair distances were changed, forcing subjects to execute a foot-strike, either very far from or near to the stair, before climbing it, so as to reveal any significant adaptations the climber would undertake to avoid slips or falls. Older and younger subjects applied appropriate visual and motor guidance by scaling their motor capabilities to the environmental dimensions.

Ecological Moral Realism: An Alternative Theoretical Framework for Studying Moral Psychology

The authors propose that the empirical study of human moral behavior as undertaken by positive psychologists, psychologists interested in the study of values, and experimental ethicists can be normative at its core, yet also remain truly scientific. To do this, those interested in the empirical study of human moral behavior should consider the concept of affordances, which is central to the Gibsonian ecological psychology tradition, as an approach to studying virtues and strengths. From this perspective, virtues can be better defined as part of moral analogues of affordances (MAAs). Just as the affordance “being-climbable” is a relation between climbing ability and height, so one can similarly define a MAA as an opportunity for moral behavior. Virtues, on this account, would be defined as abilities to behave appropriately in morally relevant situations. If one studies virtues as components of MAAs, virtues are only comprehensible in terms of morally relevant situations. Similarly, morally relevant situations are comprehensible only in terms of abilities to behave appropriately in them, that is, in terms of virtues. We believe that such an approach holds many advantages.

An Invariant Guiding Stair Descent by Young and Old Adults

In this study the author compared the perception-action capability of young and old adults (respectively, mean age 22 and 62 years old) when descending stairs and examined the relevant task constraints that guide the action. It was found that old adults selected and descended stairs that were significantly lower than young adults and showed less hip joint flexibility. However, the performance parameter, defined as the ratio between the height of the stair and the distance taken by the stepping foot to the top edge of the stair, was invariant for both groups. Thus, despite different ability levels, young and old adults are constrained by the same perception-action invariant for guiding the act of stair descent.

Scaling affordances for human reach actions

A methodology developed by Cesari and Newell [Cesari, P., & Newell, K. M. (1999). The scaling of human grip configuration. Journal of Experimental Psychology: Human Perception and Performance 25, 927-935; Cesari, P., & Newell, K. M. (2000). The body-scaling of grip configurations in children aged 6-12 years. Developmental Psychobiology 36, 301-310] was used to delineate the roles of an object's weight (W) and distance (D) as well as the actor's strength (S) in determining the macroscopic action used to reach for the object. Participants reached for objects of five different weights placed at 10 distances. The findings of a single discriminant analysis revealed that when object weight is scaled in terms of each individual's strength and reach distance is scaled in terms of each individual's maximum-seated reach distance, a single discriminant analysis was able to predict 90% of the reach modes used by both men and women. The result of the discriminant analysis was used to construct a body-scaled equation, K=lnD+ln(W/S)/36, similar in form to the one derived by Cesari and Newell, accurately predicted the reach action used. Our findings indicate that Cesari and Newell's method can identify a complex relationship between geometric and dynamic constraints that determine the affordances for different reach actions.