Amy L. Hackney

Action strategies of older adults walking through apertures.

The current study aimed to determine if the action strategies (i.e. Critical Point) of older adults when walking through apertures are different from those previously reported in young adults. Older adults (N=9) walked at a self selected pace along a 6-m path passing through a static door aperture (45-80 cm in 5 cm increments). Results showed that older adults rotate their shoulders more at apertures less than 1.6 times their shoulder width, indicating a more cautious approach. However, rotation magnitudes were highly variable at all aperture widths, but was not related to differences in stability. Therefore it appears that older adults use a body-scaled locomotor control strategy when passing through apertures.

Older adults are guided by their dynamic perceptions during aperture crossing.

Perceptions guide actions and these actions will affect perceptions (Gibson [1]). In return, these new perceptions will affect subsequent actions. The current study aimed to determine if the action differences previously observed in young and older adults are due to differences in perception and whether perceptual judgments guide action. Young (n=10) and older adults (n=9) completed two tasks; (1) judge the passability of various sized apertures during static and dynamic conditions and (2) physically pass through similar aperture sizes. The perceptual tasks required participants to give a yes/no response as to whether they could pass through an aperture (0.9-1.8 times SW (SW)) without rotating their shoulders from a distance of 5m from the aperture. During the passage through the aperture, the participants approached the aperture (1-1.8 times the SW) along a10m path at a self-selected pace and passed through the aperture using a suitable method. Results from the aperture crossing confirmed that older adults produce shoulder rotations at larger relative aperture widths than young adults and are more variable in their shoulder rotations at each aperture width. Perceptual results indicated that older adults had similar static but different dynamic perceptions than the young adults. The observed age-related differences in dynamic perceptions were most likely the result of differences in dynamic balance control.

Is the Critical Point for Aperture Crossing Adapted to the Person-Plus-Object System?

ABSTRACT When passing through apertures, individuals scale their actions to their shoulder width and rotate their shoulders or avoid apertures that are deemed too small for straight passage. Carrying objects wider than the body produces a person-plus-object system that individuals must account for in order to pass through apertures safely. The present study aimed to determine whether individuals scale their critical point to the widest horizontal dimension (shoulder or object width). Two responses emerged: Fast adapters adapted to the person-plus-object system by maintaining a consistent critical point regardless of whether the object was carried while slow adapters initially increased their critical point (overestimated) before adapting back to their original critical point. The results suggest that individuals can account for increases in body width by scaling actions to the size of the object width but people adapt at different rates.

Does the passability of apertures change when walking through human versus pole obstacles

The current study set out to evaluate how individuals walk through apertures created by different stationary obstacles. Specifically, we examined whether the passability of apertures differed between human and pole obstacles by quantifying aperture crossing behaviors such as the critical point. Participants walked an 8m path toward a visible goal located at the end. Two obstacles were positioned 5m from the starting location and participants were instructed to pass between the obstacles without hitting them. The distance between the obstacles ranged between 1.0 and 1.8× the participants shoulder width. Results revealed that, when the obstacles were humans, individuals rotated their shoulders more frequently at larger apertures, as evidenced by a larger critical point (1.7 vs 1.3 for poles), initiated shoulder rotations earlier, rotated to a larger degree, left a wider clearance between their shoulders and the obstacles at the time of crossing, and walked slower when approaching and passing through the obstacles compared to when the obstacles were poles. Furthermore, correlational analyses revealed that the amount of change between an individuals critical point for the poles and the critical point for the human obstacles was related to social risk-taking and changes in walking speed. Therefore, it appears that the passability of apertures changes when walking between two people versus two objects such that more space and greater caution are needed for human obstacles. It is possible that the greater caution observed for human obstacles is to account for the personal space needs of others that do not exist in the same extent for poles and that the degree of caution is related to social factors.

Direction of single obstacle circumvention in middle-aged children

When required to walk around a stationary object, adults use the location of the goal to set up their locomotor axis and obstacles presented along the locomotor axis will repel the individual towards the side that affords more space [1]. Research has yet to examine whether children can identify the locomotor axis and choose their paths accordingly. Therefore, the current study examined the factors that influence the direction in which children choose to deviate around a single obstacle and whether the presence or absence of a goal influences path selection and trajectory. Ten children (age: 7.1 years±0.8) walked along a 9 m path and avoided a single obstacle that was located in one of three locations (midline, 15 cm to the right or 15 cm to the left). On half the trials, an end-goal was visible from the start of the path while the other half of the trials had no visible goal. The results demonstrate that: (1) children are able to perceive and move towards more open space but are more variable when the end-goal is not visible; (2) children are capable of maintaining an elliptical-shaped protective envelope when avoiding a single obstacle regardless of whether or not the locomotor axis is established; and (3) although children are capable of choosing paths that afford the most space, the manner in which they arrive at their goal is not driven by factors similar to adults.

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.

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 participants 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.

Action strategies for walking through multiple, misaligned apertures

When avoiding obstacles, path selection is thought to be determined by the attraction of the end-goal. However for aperture crossing, it is unclear whether the attraction point originates in the center of the aperture or at the end-goal, as previous experiments align the aperture with the end-goal. The purpose of the current study was to decipher the possible location of the attraction point, by evaluating crossing behaviour for multiple, misaligned apertures. Participants were instructed to walk through three separate apertures while en route to an end-goal. The first and last apertures were fixed such that they were both either 0.9× or 1.7× shoulder width (SW) while the second aperture was either 0.9, 1.3 or 1.7× SW and shifted 25, 50 or 75cm off the midline. Findings revealed that the attraction of the end-goal, and not the middle of the aperture, guided crossing behaviour. The spatial margin decreased as the size of the shift increased. Furthermore, the frequency of rotation increased as the aperture was shifted away from midline, regardless of the aperture size. Since rotations would not normally occur for all of these aperture sizes when aligned with the end-goal, these results suggest that rotations were produced in an attempt to keep ones trajectory as close to the midline as possible. Therefore, not only does the attraction of the goal guide path trajectory, but individuals will choose to reduce the spatial margin and rotate the shoulders when walking through misaligned apertures, likely in attempt to maintain the straightest possible path.