The addition of stripes (a version of the 'horizontal-vertical illusion') increases foot clearance when crossing low-height obstacles

Balance recovery after trips is affected by the type of tripping obstacles

Occupational falls are often initiated by trips. Mechanical perturbations applied onto the tripped foot are different for different types of tripping obstacles. The present study aimed to determine how different types of tripping obstacles affect balance recovery after trips. Sixty-four healthy adults participated in an experimental study. They were instructed to perform several walking trials, during which two trips were randomly induced, one by a pole-like obstacle and the other by a board-like obstacle. Balance recovery after trips was measured and compared between the two obstacles. Results showed that the board-like obstacle led to longer step-off time, shorter recovery step duration, and smaller minimum hip height, suggesting that the risk of trip-initiated falls could be higher with the board-like obstacle vs. the pole-like obstacle. This finding presents the need for future research to consider the influence of obstacle type when exploring mechanisms for trips and falls.

Deceptive illusory cues can influence orthogonally directed manual length estimations

We examined participants' abilities to manually estimate one of two perpendicular line segment lengths using curved point-to-point movements. Configurations involved symmetrical, unsymmetrical, and no bisection in upright and rotated orientation alterations to vertical-horizontal (V-H) illusions, where people often perceive longer vertical than horizontal segments for equal segment lengths. Participants used two orthogonally directed movements for length estimations: positively proportional (POS) - where greater fingertip displacement involved longer length estimation between configuration intersection start position and fingertip end, and negatively proportional (NEG) - where greater fingertip displacement from the screen edge start position toward configuration intersection involved a shorter length estimation between configuration intersection and fingertip end. Length estimations followed most standard perceptual aspects of the V-H illusion for POS estimations, yet differed between upright and rotated orientations for the symmetrical configuration. NEG estimations revealed no illusory influences. Use of allocentric programming likely accompanied POS estimations to explain V-H illusory influences on perceptuomotor control.

Visual Illusion Created by a Striped Pattern Through Augmented Reality for the Prevention of Tumbling on Stairs

A fall on stairs can be a dangerous accident. An important indicator of falling risk is the foot clearance, which is the height of the foot when ascending stairs or the distance of the foot from the step when descending. We developed an augmented reality system with a holographic lens using a visual illusion to improve the foot clearance on stairs. The system draws a vertical striped pattern on the stair riser as the participant ascends the stairs to create the illusion that the steps are higher than the actual steps, and draws a horizontal striped pattern on the stair tread as the participant descends the stairs to create the illusion of narrower stairs. We experimentally evaluated the accuracy of the system and fitted a model to determine the appropriate stripe thickness. Finally, participants ascended and descended stairs before, during, and after using the augmented reality system. The foot clearance significantly improved, not only while the participants used the system but also after they used the system compared with before.

Step edge highlighters and illuminance changes influence stair descent in a real-world setting

Studies investigating the effect of tread edge highlighters on descent speed differ, but collectively report the potential benefit of reduced fall risk. Here we examine the impact of adding high-contrast black vinyl striping to the front edge of each step's tread and its impact on descending gait speed (intervention), while controlling for illumination. Descending gait speed was estimated from 5,824 video observations using the stairway length and entry and exit times. A second stairway was unaltered (control) to compare to the intervention. Stair users were primarily 18-30 years old with a small percentage being middle-aged and older adults. Descending gait speed was significantly slower on the intervention stairway (Linear mixed effects model: standardised coefficient = -0.07, 95% CI = [-0.12, -0.02], p = .010) compared to the control and may be impacted by illuminance. We propose that the slowed gait speed could be due to changes in gait kinematics (e.g. foot clearance) and may reduce fall-risk. Practitioner summary: Tread-edge contrast enhancement could be a low-cost means to reduce fall-risk on stairways, but its impact on gait kinematics is not well understood. We found that contrast enhancement reduced descending gait speed, but descending gait speed's impact on fall risk reduction ultimately requires further investigation.

Shape of an obstacle affects the mediolateral trajectory of the lower limb during the crossing process

In previous studies involving obstacle crossing, vertical foot clearance has been used as an indicator of the risk of contact. Under normal circumstances, individuals do not always cross over obstacles with the same height on both sides, and depending on the shape of the obstacle, the risk of contact may differ depending on the foot elevation position. Therefore, we investigated whether task-related control of the mediolateral foot position is adapted to the shape of the obstacle. Sixteen healthy young adults performed a task in which they crossed over two obstacles with different shapes while walking: a trapezoidal obstacle and a rectangular obstacle, as viewed from the frontal plane. It was shown that when crossing over a trapezoidal obstacle, the participants maintained foot clearance by controlling the mediolateral direction, which chose the height that needed to be cleared. The results of this study suggest that the lower limb movements that occur during obstacle crossing are controlled not only in the vertical direction but also in the mediolateral direction by adjusting the foot trajectory to reduce the risk of contact. It was demonstrated that control was not only based on the height of the obstacle directly under the foot but also in the foot mediolateral direction, considering the shape of the entire obstacle, including the opposite limb.

Vertical-horizontal illusory effects with gaze restrictions do not change length estimations using the lower limb

Gaze direction and use of visual feedback can affect illusory influences over perceptions and manual length size estimates of the vertical-horizontal (V-H) illusion, in which the vertical, bisecting segment of an inverted T (IT) appears longer than the horizontal, bisected segment. We questioned whether V-H illusory influences would also exist for the lower limb. Participants stepped forward in an attempt to make the toe-to-toe distance of their dominant foot equal to a short or long bisecting segment length of a vertically projected IT. Performances under three gaze conditions included: maintaining gaze on the IT intersection throughout a trial for target fixation (TF); viewing the intersection for 4 s then looking down and performing the step for movement fixation (MF); and viewing the intersection for 4 s then maintaining gaze on the remembered location of the intersection and performing the step for remembered target fixation (RTF). Variables included step displacement, peak velocity (PV), and normalized ground reaction force amplitude (GRFampN), as well as time to peak and peak amplitude of the center of pressure (COPtime and COPamp, respectively). Main effects of gaze on PV, GRFampN, COPtime, and COPamp revealed lower values for MF compared to TF and RTF, which did not exist for step displacement. No significant correlations existed between step displacement and other variables across participants. Together, we found evidence to suggest differences between movement planning and movement completion. Exploitation of deceptive visual cues can guide step planning and early step execution, but do not guide final step estimations.

Using a stair horizontal-vertical illusion to increase foot clearance over an inconsistently taller stair-riser

Introduction

Stair falls can be caused by inconsistent stair dimensions. During ascent, inconsistently taller stair risers lead to reduced foot clearances as the inconsistency goes unnoticed. A stair horizontal-vertical illusion increases perceived riser heights and foot clearance and could offset reduced foot clearances over inconsistently taller risers, though this might impact other stair safety measures.

Method

Twelve participants (age: 22 (3) years) ascended a seven-step staircase under three conditions: i) all steps consistent in riser height (consistent), ii) a 1cm increase in step 5 riser height (inconsistent) and iii) a 1cm increase in step 5 riser height, superimposed with a stair horizontal-vertical illusion (illusion). Vertical foot clearance, foot overhang, and margins of stability were assessed over step 4, 5 and 6. Perceived riser height due to the illusion was determined through a computer perception test. A One-Way Repeated Measures ANOVA compared biomechanical variables between conditions. A One Sample t test compared perceived riser height to the true height.

Results

Over the inconsistent step 5, foot clearance reduced by 0.8cm compared to consistent. Illusion increased foot clearance by 1.1cm and decreased foot overhang by 4% compared to inconsistent. On step 4 the illusion led to more anterior instability compared to inconsistent. Illusion and inconsistent led to more mediolateral stability compared to consistent. The illusion increased perceived riser height by 12%.

Discussion

Foot clearance reductions over inconsistently taller risers can be offset by a stair horizontal-vertical illusion. Additional benefits included a safer foot overhang and unaffected stability over the inconsistent riser. Changes to step 4 stability might have resulted from leaning forward to look at the step 5 illusion. The stair horizontal-vertical illusion could be a practical solution for inconsistently taller stair risers, where a rebuild is usually the only solution.

Gaze Direction Changes the Vertical-Horizontal Illusory Effects on Manual Length Estimations

We examined potentially deceptive influences of the vertical-horizontal (V-H) illusion on manual length estimations. When viewing V-H illusory configurations, people perceive that the bisecting segment length exceeds the bisected segment length when segments are actually equal. Participants used downward or rightward pointing movements to manually estimate the length of a short bisecting segment of the V-H illusion in upright or rotated configurations. Participants directed their gaze freely, on the configuration, or on the movement space. Manual length estimations for upright and rotated configurations depended on gaze direction, revealing bisection influences only for restricted viewing. People produced illusory influences on perceptuomotor control only when gaze was directed toward V-H configurations or their movement. Exploitation of deceptive visual cues can direct upper limb control for sensorimotor coordination.