title: The horizontal-vertical illusion on stairs: optimising the visual appearance of stairs to reduce falls risk
Creators: name: Skervin, T
Publisher: name: Liverpool John Moores University
Year: 2021

description: Stairs are a common location for a fall and are a significant cause of injury or accidental death in older adults. Falls on stairs can be multifactorial but often occur because of a trip. Tripping on stairs may result when step dimensions/edges are difficult to discern due to the stair appearance. Previous work has developed a stair horizontal-vertical illusion which, when placed on a step, increases the perceived riser height and stair ascent foot clearances. The illusion could help to reduce stair falls, though there are several unaddressed points which importantly could affect its intended use. 1) In its current form, the illusion may not be visually suitable for older adults, those with photosensitivity or on real world stairs. 2) The perception-action link described has not been explicitly evidenced in older adults. 3) Studies have not tested the illusion on an inconsistently taller riser which can cause a trip. 4) There is also a need to develop methods that can assess foot clearance on real world stairs. Current methods are restricted by either reduced portability of equipment, low accuracy, or complex setups limiting their use for measuring foot clearances in response to the illusion on real world stairs. To address these points, a series of studies were conducted: Study 1 determined whether modified stair horizontal-vertical illusions (reduced number of vertical riser stripes (spatial frequency) and changes to the spacing of the vertical stripes (mark space ratio)) led to increases in perceived riser heights through a series of computer-based perception tests in young (N=42: 24 ± 3 years) and older adults (N=14: 70 ± 6 years). All stair horizontal-vertical illusion designs across each test led to significant increases in the perceived riser height in both young and older adults (12-19% increase) with no differences between age groups, suggesting the stair horizontal-vertical illusion can be modified and still cause an increase in perceived riser height. Study 2 assessed whether increases in perceived riser height due to the modified illusions were linked to increases in stair ascent foot clearance (perception-action link) and whether this impacted other stair safety measures in sixteen older (70 ± 7 years) and fifteen young (24 ± 3 years) adults. Each stair horizontal-vertical illusion led to an increase in vertical foot clearance for young (up to 0.8cm) and older adults (up to 2.1cm) as well as increases in perceived riser height (young; 13% increase, older; 11% increase) demonstrating a perception-action link. Other stair safety measures were not adversely affected by the modified illusions. Study 3 determined whether a modified stair horizontal-vertical illusion (70-30% mark space ratio) could ameliorate reduced foot clearances that typically occur over an inconsistently taller mid-stair riser (1cm increase in this study) and whether this impacted other stair safety measures. Foot clearance reduced over the inconsistently taller riser (0.8cm) indicating participants did not adapt to the inconsistency. Placing a modified stair horizontal-vertical illusion onto the inconsistency increased foot clearance by 1.1cm thereby ameliorating the foot clearance reduction. The illusion also led to a safer foot overhang. The stair horizontal-vertical illusion could be a practical solution for inconsistently taller stair risers, where a rebuild is usually the only solution. Study 4 assessed the accuracy and precision of a custom photogate setup that measures foot clearance on stairs, compared to an optoelectronic system (Vicon). The photogates showed very good accuracy when compared to Vicon (mean difference of 0.15cm) though less agreement was found in the measurement precision between the two systems (upper and lower limits of agreement 1.27cm and -1.58cm, respectively). A very strong positive correlation between the two systems was also found (r = .83, n = 294, p