An examination of adaptive behaviour when stepping onto moving surfaces
: an affordances and agency perspective

  • Rhys Hunt

Student thesis: Doctoral Thesis


Fall-related injuries during daily locomotion suggest that ‘every-day’ challenges exceed the capabilities of some pedestrians, with older adults a particular at risk population. Indeed, stepping onto moving surfaces (such as escalators and travellators), represents one every-day locomotor challenge that can lead to accidents. This thesis aimed to examine the perceptual-motor behaviours that underpin successful locomotion as younger and older adults negotiate the challenge of stepping onto moving surfaces, and subsequently explore the use of environmental design as a means of soliciting behaviour change. To achieve this, an integration of optoelectronic motion capture and mobile eye-tracking was used during a series of experiments, which examined: (i) how 12 younger (18-40 years) and 15 older (>60 years) adults stepped onto static and moving surfaces (with and without accuracy demands); (ii) how these participants adapted perceptual-motor behaviours when high contrast demarcation lines and foot targets were added to the moving surface; and (iii) how 11 younger and 14 older adults adapted their perceptual-motor behaviours when a high contrast foot target line was added to the walkway approaching the moving surface.
Results showed that step length increased when stepping onto moving surfaces (younger adults: 62.9cm and 68.6cm; older adults: 59.1cm and 62.0cm; static and moving surfaces, respectively) but reduced when accurate movement was demanded (younger adults: 67.8cm and 63.8cm; older adults: 63.3cm and 59.8cm; no accuracy and accuracy demand, respectively), suggesting environmental design solicited different behaviours. Likewise, design interventions, such as demarcation lines and foot targets added to the simulated escalator environment, invited different behavioural adaptations. Increasing visual salience - adding high contrast lines and/or foot targets to the moving surface - resulted in significantly later gaze transfer from the final walkway footstep location compared to conditions without salient features. A foot target positioned on the approach to the moving surface reduced walkway viewing by 11.32% and increased moving surface viewing by 11.62%, indicating feed-forward control.
Younger and older adults’ behaviours consistently differed. Older adult approach times (between 0.15s and 0.19s) were more variable than younger adults (between 0.08s – 0.11s) when overcoming environmental challenges, indicating that older adults adapted their approach to a greater extent. Moreover, interventions invited different behaviours between age groups. The approach target line invited later gaze transfer in younger adults preceding final walkway foot contact, but earlier gaze transfer in older adults (younger adults transferred gaze 332ms and 237ms; older adults transferred gaze 247ms and 447ms; no target and target conditions, respectively). Such differences suggest that, unlike younger adults, older adults did not adopt online control, which may be due to the limits of their action capabilities.
Overall, this thesis demonstrates that differences in adaptive perceptual-motor behaviours between younger and older adults arose from functional differences in their action capabilities and properties of the moving surface environment. Subsequently, the thesis also provides evidence to help inform safety policy and improve escalator user safety.
Date of AwardJan 2022
Original languageEnglish
Awarding Institution
  • University of Portsmouth
SupervisorMatt Miller-Dicks (Supervisor) & Chris Mills (Supervisor)

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