Age-related changes in gaze sampling strategies during obstacle navigation

Designing Combinations of Pictogram and Text Size for Icons: Effects of Text Size, Pictogram Size, and Familiarity on Older Adults' Visual Search Performance

OBJECTIVE

This study aimed to determine suitable combinations of text and pictogram sizes for older adults and investigated the visual prioritization of pictogram versus text.

BACKGROUND

Icons have become an indispensable part of application (app) design. Pictogram size and text size of icons influence the usability of apps, especially by aged users. However, few studies have investigated the influences of different pictogram and text size combinations on readability, legibility, and visual search performance for older adults.

METHOD

This study used eye-tracking technology to investigate the effects of different pictogram and text size combinations as well as familiarity on readability, legibility, and visual search performance for older adults. A 3 (pictogram size) × 3 (text size) × 2 (familiarity) repeated-measures experimental design was used.

RESULTS

The results of this study suggest that pictogram size and text size significantly affect visual search performance and that familiarity moderates the effect of text size on distribution of fixation duration proportion for text and pictograms.

CONCLUSION

Large pictogram and text sizes improved the readability and legibility of icons for older adults. Furthermore, the older adults fixated the area of text prior to pictograms when the pictogram size was larger than 72 × 72 px (1.38° × 1.38°) in the visual search task.

APPLICATION

The results of this study suggest using different combinations of pictogram and text sizes for older adults under different scenarios. The findings of this study act as practical support for designers and developers of mobile apps for older adults.

The visual control of locomotion when stepping onto moving surfaces: A comparison of younger and older adults

Stepping between static and moving surfaces presents a locomotor challenge associated with increased injury frequency and severity in older adults. The current study evaluates younger and older adults' behaviours when overcoming challenges sampling moving walkway and escalator environments. Twelve younger adults (18-40 years, Male = 8) and 15 older adults (60-81 years, Male = 5) were examined using an integration of optoelectronic motion capture and mobile eye-tracking. Participants were investigated approaching and stepping onto a flat conveyor belt (static or moving; with or without surface (demarcation) lines). Specifically, the four conditions were: (i) static surface without demarcation lines; (ii) static surface with demarcation lines; (iii) moving surface without demarcation lines; and (iv) moving surface with demarcation lines. A two (age group) x two (surface-condition) x two (demarcation-condition) linear mixed-model revealed no main or interaction effects (p > .05) for perturbation magnitude, indicating participants maintained successful locomotion. However, different adaptive behaviours were identified between conditions with moving and accuracy demands (e.g., moving surfaces increased step length, demarcations reduced step length). Between subject effects identified differences between age groups. Older adults utilised different behaviours, such as earlier gaze transfer from the final approach walkway step location. Overall, the current study suggests that adaptive behaviours emerge relative to the environment's specific demands and the individual's action capabilities.

Effects of age on the visuo-locomotor control used to circumvent a virtual pedestrian with different limb movements

It is known that young adults (YA) circumvent pedestrians differently than inanimate obstacles and that limb movements of the pedestrian influence minimum clearance for predictable pedestrian paths. Although older adults (OA) use more cautious strategies for general pedestrian avoidance compared to YA, how pedestrian movements influence circumvention by OAs is unknown. The aim of this study was to understand how limb movements of a pedestrian with an initially unpredictable trajectory affect circumvention control in younger vs older healthy adults. Fourteen YA and 14 OA (> 70 years) were immersed in a virtual shopping mall and instructed to circumvent a virtual pedestrian (VP) approaching with either normal locomotor movements, upper limbs fixed, lower limbs fixed, or both upper and lower limbs fixed. Onset distance for trajectory deviation, minimum clearance, walking speed, body segment yaw angles and gaze behaviour were analysed. When the VP lacked local limb movements, both age groups initiated their trajectory deviations farther away, but significantly more so for OA. Minimal clearance was unchanged across conditions and similar for both age groups. OA walked slower, produced smaller head and trunk yaw, and visually focused on the VP for a greater percentage of time. Thus, lack of limb movements of another pedestrian resulted in more cautious circumvention control and OA needed more time to process visual information with greater visual attention focused on the VP. Age-related changes could translate to a greater risk of falls in OA populations with reduced balance and mobility that could limit community ambulation.

Target position and avoidance margin effects on path planning in obstacle avoidance

This study examined how people choose their path to a target, and the visual information they use for path planning. Participants avoided stepping outside an avoidance margin between a stationary obstacle and the edge of a walkway as they walked to a bookcase and picked up a target from different locations on a shelf. We provided an integrated explanation for path selection by combining avoidance margin, deviation angle, and distance to the obstacle. We found that the combination of right and left avoidance margins accounted for 26%, deviation angle accounted for 39%, and distance to the obstacle accounted for 35% of the variability in decisions about the direction taken to circumvent an obstacle on the way to a target. Gaze analysis findings showed that participants directed their gaze to minimize the uncertainty involved in successful task performance and that gaze sequence changed with obstacle location. In some cases, participants chose to circumvent the obstacle on a side for which the gaze time was shorter, and the path was longer than for the opposite side. Our results of a path selection judgment test showed that the threshold for participants abandoning their preferred side for circumventing the obstacle was a target location of 15 cm to the left of the bookcase shelf center.

Visuomotor control dynamics of quiet standing under single and dual task conditions in younger and older adults

Visual input facilitates stable postural control; however, ageing alters visual gaze strategies and visual input processing times. Understanding the complex interaction between visual gaze behaviour and the effects of age may inform future interventions to improve postural control in older adults. The purpose of this study was to determine effects of age and dual task on gaze and postural sway dynamics, and the sway-gaze complexity coupling to explore the coupling between sensory input and motor output. Ten older and 10 younger adults performed single and dual task quiet standing while gaze behaviour and centre of mass motion were recorded. The complexity and stability of postural sway, saccade characteristics, visual input duration and complexity of gaze were calculated in addition to sway-gaze coupling quantified by cross-sample entropy. Dual tasking increased complexity and decreased stability of sway with increased gaze complexity and visual input duration, suggesting greater automaticity of sway with greater exploration of the visual field but with longer visual inputs to maintain postural stability in dual task conditions. In addition, older adults had lower complexity and stability of sway than younger adults indicating less automated and stable postural control. Older adults also demonstrated lower gaze complexity, longer visual input durations and greater sway-gaze coupling. These findings suggest older adults adopted a strategy to increase the capacity for visual information input, whilst exploring less of the visual field than younger adults.

Gaze behavior during pedestrian interactions in a community environment: a real-world perspective

Locomotor adaptations, as required for community walking, rely heavily on the sense of vision. Little is known, however, about gaze behavior during pedestrian interactions while ambulating in the community. Our objective was to characterize gaze behavior while walking in a community environment and interacting with pedestrians of different locations and directions. Twelve healthy young individuals were assessed as they walked in a shopping mall from a pre-set location to a goal located 20 m ahead. Eye movements were recorded with a binocular eye-tracker and temporal distance factors were assessed using wearable sensors from a full-body motion capture system. Participants exhibited more numerous and longer gaze episodes on pedestrians (GEP) that were walking in the same direction as themselves vs. those that were in the opposite direction. The relative durations of GEPs, however, showed no significant differences between pedestrians walking in the same vs. opposite direction. Longer durations of GEPs were also observed for centrally located pedestrians compared to those located on either side, but this was the case only for pedestrians that were walking in the same direction as participants. In addition, pedestrians in the centre, and even more so those on the right, were fixated at farther distances compared to those on the left. Results indicate that healthy young individuals modulate their gaze behavior as a function of the location and direction of pedestrians when ambulating in a community environment. The observed modulation is interpreted as being caused by an interplay between collision risk, pedestrian visibility, presence of leaders and social conventions (right-sided circulation). Present results also establish baseline measures for the quantification of defective visuomotor strategies in individuals with mobility disorders.