Body-scaled Information Research Articles

The effects of human following behaviours on decision making during aperture crossing scenarios

BackgroundEveryday locomotion often requires that we navigate crowded and cluttered environments. Individuals navigating through nonconfined space will require a deviation from the straight path in order to avoid apertures smaller than 1.4 times their shoulder width. When in a crowd, humans will follow the behaviours of those directly in front of them, making changes to their walking speed and direction heading based on the changes made by the people they are following. Research QuestionThe current study aimed to discover whether the decisions made by young adults regarding the passability of an aperture would be influenced by the presence of a leader completing the same nonconfined aperture crossing task. MethodsParticipants (N = 24) walked in a virtual reality environment along a 6.5 m pathway towards a goal while avoiding two virtual poles which created an aperture (0.8–1.8 times the participants’ shoulder widths). For some trials, a sex-matched avatar (shoulder width of 0.8, 1.0, or 1.2 times the participants’ shoulder widths) completed the aperture crossing task, using its own body-scaled information, ahead of the participant. ResultsParticipants walked through apertures smaller than 1.4 times their shoulder width (i.e. critical point) regardless of avatars’ independent behaviours. Participants began to deviate 3.69 m from the aperture on all trials that required a deviation and approached their goal at a slower speed when the avatar was present. SignificanceThis study demonstrates that during a nonconfined aperture crossing task, individuals are not influenced by human following behaviours and will continue to make decisions based on their own body-scaled information.

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 ± 1.5years, 10 males) were instructed to walk along a 10m 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 2.5m 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.

Effect of Body-Scaled Information on Reaching in Children With Hemiplegic Cerebral Palsy

This study examined body-scaled information that specifies the reach patterns of children with hemiplegic cerebral palsy and children with typical development. Nine children with hemiplegic cerebral palsy (3-5 years) and 9 age-matched children with typical development participated in the study. They were required to reach and grasp 10 different pairs of cubes. Reach data were coded as either a 1-handed reach or a 2-handed reach. Dimensionless ratios were calculated by dividing the cube size by the maximal aperture between the index finger and thumb. A critical ratio was used to establish the shift from a 1-handed to an exclusive 2-handed reach. The critical ratio was not significantly different for either preferred or nonpreferred arms within and between groups. All children used an exclusive 2-handed reach at a similar dimensionless ratio. Our study provides evidence of the "fit" between environment (cube size) and the individual's capabilities (finger aperture) for reaching for both groups.

Commentary on “Effect of Body-Scaled Information on Reaching in Children With Hemiplegic Cerebral Palsy

Commentary on “Effect of Body-Scaled Information on Reaching in Children With Hemiplegic Cerebral Palsy

Action strategies of individuals during aperture crossing in nonconfined space

Walking through cluttered environments is a requirement of everyday locomotion, and individuals will walk toward open space and adjust their actions in order to prevent injury. When walking in a confined space, individuals require a shoulder rotation to pass through apertures smaller than 1.3 times their shoulder widths. The current study aimed to identify the action strategies employed by young adults to avoid contacting two obstacles placed in the travel path when walking in a nonconfined space. Participants (N = 12) walked along a 10-m path towards a goal while avoiding two vertical obstacles specifically placed to create an aperture (of 0.6 to 1.8 times the participants' shoulder widths) on opposite sides of the travel path midline. Results showed that participants walked around obstacles that were separated by less than 1.4 times their shoulder width (i.e., critical point). When participants deviated from their initial travel path, they did so by maintaining a consistent protective zone, regardless of the aperture width. The protective zone had dimensions of 3.80m in the plane of progression and of 0.30 m between themselves and the obstacles at the time of crossing. This study demonstrates that individuals use body-scaled information to control actions in nonconfined space similar to that used in confined space.

Young and older adults use body-scaled information during a non-confined aperture crossing task

Young and older adults demonstrate differences in action when passing through confined spaces (Warren and Whang in J Exp Psychol Hum Percept Perform 13:371-383, 1987; Hackney and Cinelli in Gait Posture 33:733-736, 2011). However, it is unknown whether or not these differences in actions exist during non-confined multiple obstacle avoidance tasks. The current study aimed to determine: (1) the differences in actions between young and older adults when given a choice in path selection and (2) establish the variables that may account for these differences in action. Older adults (N=12) and young adults (N=12) walked along a 10-m path towards a goal and avoided two vertical poles placed halfway down the path on either side of the midline (ranging between 0.6 and 1.8× shoulder width). Results revealed that in non-confined space, both age groups use body-scaled information to determine the passability of apertures and maintain similar Critical Points to those reported in confined aperture crossing (1.4 for young adults and 1.6 for older adults). Variability of the medial-lateral centre of mass movement (i.e. how much the trunk moved side to side) between the groups most likely accounted for the larger aperture sizes (i.e. Critical Points) required by the older adults to pass through the apertures. Therefore, it appears that body-scaled information may include an individual's knowledge of both actual body size and body sway magnitude.

The Impact of Body-Scaled Information on Grasping Action in Toddlers with and without Down Syndrome

Background and purpose: Studies of adults and typically developing (TD) children find the number of hands and fingers used to grasp an object is influenced by the relationship between object size and hand size. Children with Down syndrome (DS) between 3 and 11 years have shown no differences in number of hands (1 or 2 hands) used to grasp different sized objects compared to TD children when the object size was body-scaled. The purpose of this study was to examine whether body-scaled information affected the number of hands and fingers used to grasp different sized objects in toddlers with and without DS. Method: Ten toddlers were included, 5 DS ( = 16 mo) and 5 age-matched TD ( = 16.3 mo). Subjects were videotaped grasping 14 boxes, 1.4 cm to 13.5 cm. in size. Number of hands and fingers used for grasping were recorded. Descriptive statistics, t-tests and Spearman correlation coefficient were used to compare the differences between toddlers with DS and TD. Results: Toddlers with DS had significantly smaller hand length than toddlers without DS (p=.004 right hand, p=.007 left hand). As box size increased, both groups switched from one-hand to two-hand grasping. There was a significant difference between groups where this transition occurred (p=.02). However, when the body-scaled ratio between object size and hand size was considered, the differences between groups disappeared (t(8)=1.479; p=.18). Moreover, the number of fingers used to grasp boxes also increased with increasing box size across both groups (ρ=0.94). Conclusion: Toddlers with DS show similar body-scaled grasping pattern as their age-matched peers with TD indicating that the differences in grasping patterns between toddlers with and without DS may be attributed to differences in body size, besides the motor abilities.

The Impact of Body-Scaled Information on Reaching

Environmental and task modifications are powerful methods used to affect action in rehabilitation and are frequently used by therapists. 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. This was a cross-sectional prospective study. 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. 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. The relational metrics between the cube and hand are only one contribution to the emergent reaching and grasping patterns. 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.

Influences of Shoulder Widths on Aperture Passage in an Environment-Person-Person System

The study was aimed to investigate the perception of individual's affordances for aperture passage in an environment-person-person system, and the influence of the shoulder width on aperture passage. Nine wide-shoulder and 9 narrow-shoulder undergraduates served as perceivers while another 9 wide-shoulder and 9 narrow-shoulder undergraduates served as companions. Perceivers and companions stood side by side as a dyad and then the perceivers were required to make judgments about the dyads' minimal passable aperture width. The dyads then walked side by side toward the aperture to determine the minimal passed aperture width of the system. The results indicated that despite the shoulder widths of the companions, the perceived minimal aperture width correlated with but different from the actual minimal aperture width. When the ratio between aperture width and the shoulder width of the perceiver + companion was taken into consideration, the ANOVA indicated that the differences between shoulder widths disappeared in both the perceived and actual passed conditions. The perception of the perceivers' affordances for aperture passage for the environment-person-person system was based on the shoulder widths of the perceiver and companion. Individuals were able to perceive affordances for an environment-person-person system based the body-scaled information of a dyad.

Perceiving Affordances for Aperture Passage in an Environment–Person–Person System

ABSTRACT The authors investigated the perception of affordances for aperture passage in an environment–person–person (E–P–P) system, which comprised an adult perceiver and a child as a companion. Perceivers were 8 large and 8 small female undergraduates and were companioned with 1 large and 1 small girl. The perceivers perceptually judged the minimum aperture width for the E–P–P system, and then the adult–child dyads (a pair of people) actually walked through to determine the system's actual minimum aperture width. Results demonstrated that perceivers precisely judged the action capabilities of an E–P–P system on the basis of the body-scaled information of each adult–child dyad. The findings extended the previous concept of affordances for an environment-person system to affordances for an E–P–P system.

Body-scaled transitions in human grip configurations.

This article reports two experiments that were set up to examine the preferred human grip configuration used to displace cubes that varied in length (Lc), mass (Mc), and density (ML3). In particular, the authors sought to provide a more precise test of a dimensional relation between the object and the hand that had previously been shown to predict the grip configuration used to transport an object from one location to another. The experiments examined 2 grip transitions (from 3 digits to 4 digits and from 1 hand to 2 hands) within 2 sets of object conditions. In Experiment 1, cubes with a low density and a small increment in size (1 mm) were used, whereas in Experiment 2, cubes with 2 fixed sizes and small increments in mass were used. The results showed that the body-scaled equation K = logLc + (logMc/a + bMh + cLh), where Mh and Lh are the anthropometric measures of the hand mass and length and a, b, and c are empirical constants, is the body-scaled information that predicts the grip configurations used to displace objects.

Locomoting through apertures of different width: a study of children with cerebral palsy.

Whether children with cerebral palsy (CP) differ from non-handicapped (NH) children was studied, using body-scaled information about the passability of a doorway-like opening. There were 55 children of whom 23 were NH and 32 had CP, the latter consisting of 12 who could stand and walk unaided (CP-Walk) and 20 confined to a wheelchair (CP-Wheel). All groups were divided into two age ranges (5-8 and 9-13 year) and were tested on two occasions separated by an interval of 12 months. On both occasions, testing involved three consecutive tasks: making perceptual (pre)judgments about the passability of an opening varying in width, actually attempting to locomote through the openings (performance), and another round of (post)judgments. Judgments and performance were expressed in terms of absolute and relative outcomes, the latter differing from the former in accounting for differences in body width relative to aperture width. There were two main findings. Firstly, the younger CP-Walk children were the least able to employ body-scaled information in judging aperture width and the older CP-Wheel and NH the most able. Secondly, when performances in passing through the openings were adjusted for differences in body width, all groups had similar outcomes. This findings lends credence to the notion that when action is used in the service of perception, this is beneficial for the visual-spatial abilities of both NH and CP children. The study concludes by pointing out future directions in this type of research as well as some of the clinical implications of the findings.

Visual guidance of passing under a barrier

The theory of affordances proposes that organisms control their actions according to the fit between the organism and the environment. This study set out to examine the proposal that actions are attuned to environmental demands on the basis of body-scaled information and how modifications to such actor–environment synergies might be influenced by speed of locomotion and locomotor ability. The paradigm task was walking and running under a barrier set at different heights. The subject groups comprised normal adults, nursery school children, cerebral palsied children, and infants with less than 6 weeks' independent walking experience. A body-scaled critical point, at which they began to duck under the barrier, was observed for all but the infant subjects. In addition, the nursery school children were found to be more cautious in their behaviour than adults both when walking and running. The cerebral palsied children compensated for their poorer ability to control vertical position in space by allowing an even greater safety margin when passing under the barrier. The results provide support for an affordance theory of perception, in which body size, speed of locomotion and level of motor control are considered important properties of the actor–environment fit. ©1997 John Wiley & Sons, Ltd.

Visual guidance of passing under a barrier

The theory of affordances proposes that organisms control their actions according to the fit between the organism and the environment. This study set out to examine the proposal that actions are attuned to environmental demands on the basis of body-scaled information and how modifications to such actor–environment synergies might be influenced by speed of locomotion and locomotor ability. The paradigm task was walking and running under a barrier set at different heights. The subject groups comprised normal adults, nursery school children, cerebral palsied children, and infants with less than 6 weeks' independent walking experience. A body-scaled critical point, at which they began to duck under the barrier, was observed for all but the infant subjects. In addition, the nursery school children were found to be more cautious in their behaviour than adults both when walking and running. The cerebral palsied children compensated for their poorer ability to control vertical position in space by allowing an even greater safety margin when passing under the barrier. The results provide support for an affordance theory of perception, in which body size, speed of locomotion and level of motor control are considered important properties of the actor–environment fit. ©1997 John Wiley & Sons, Ltd.

Visual guidance of walking through apertures: body-scaled information for affordances.

A necessary condition for visually guided action is that an organism perceive what actions are afforded by a given environmental situation. Warren (1984) proposed that an affordance such as the climbability of a stairway is determined by the fit between properties of the environment and the organism and can be characterized by optimal points, where action is most comfortable or efficient, and critical points, where a phase transition to a new action occurs. Perceiving an affordance, then, implies perceiving the relation between the environment and the observer's own action system. The present study is an extension of this analysis to the visual guidance of walking through apertures. We videotaped large and small subjects walking through apertures of different widths to determine empirically the critical aperture-to-shoulder-width ratio (A/S) marking the transition from frontal walking to body rotation. These results were compared with perceptual judgments of "passability" under static and moving viewing conditions. Finally, we tested the hypothesis that such judgments are based on intrinsic or body-scaled information specifying aperture width as a ratio of the observer's eyeheight. We conclude (a) that the critical point in free walking occurs at A/S = 1.30, (b) that static monocular information is sufficient for judging passability, and (c) that the perception of passability under such conditions is based on body-scaled eyeheight information.

Visual guidance of walking through apertures: Body-scaled information for affordances.

Visual guidance of walking through apertures: Body-scaled information for affordances.