The Impact of Meaningful Vibrotactile Displays on User Preferences Across Age Groups in Automated Driving

Abstract

Automated vehicles may enhance the quality of life by empowering individuals and promoting independent mobility, especially for older adults. However, takeovers are still required occasionally. To ensure a safe transition during the takeover, meaningful tactile displays as takeover requests could be a good option to improve takeover efficiency. Previous studies have examined the effects of tactile takeover request more from an objective perspective, however, subjective evaluations that could reach larger and more diverse sample sizes have not been extensively conducted yet. Therefore, the goal of this study was to investigate drivers of different age groups (younger and older adults) on their preference of vibrotactile displays, varied in information formats (instructional and informative) and locations (seat back and seat pan), on a large population scale (n = 353) through a national survey. The results indicated a preference for informative patterns over instructional patterns and displays on the seat back over the seat pan. Also, a higher level of perceived urgency was noted in older participants (age ≥ 65) compared with younger participants. These findings may inform the design of next-generation tactile interfaces in automated systems.

Older adults (aged 65 years or above) have become the fastest-growing age population (United Nations, 2019). General age-related declines may limit their daily task performance, such as driving. Automated vehicles may help to maintain their independent mobility. However, these vehicles are still semi-autonomous, requiring human takeover, and are challenging for older adults (McDonald et al., 2019). One of the approaches to enhance takeover performance is to improve the design of the takeover requests.

Previous studies have shown that conveying takeover requests through the tactile modality results in faster response times compared to visual or auditory modalities, especially when more visual and auditory resources are needed (Brewster & Brown, 2004; Kim & Schneider, 2020). Using vibrotactile displays as takeover requests, placed on either the seat back or pan, has mainly been studied in two information formats: (1) instructional signal (i.e., instruct drivers on how to maneuver) and (2) informative signal (i.e., inform drivers where the danger comes from) (see a review, Martinez & Huang, 2022). For example, Huang and Pitts (2023) compared the effects of vibrotactile display presentation locations and information formats using an in-lab study with 40 younger participants (mean age = 23.1). The results showed that abstract signals (signals without meaningful patterns and only serving for warning purposes) were found to have better takeover performance (e.g., shorter response times) compared to the instructional tactile signals when mounted either on the seat back or the seat pan. However, findings related to the information formats, as well as the location effects, were mainly measured objectively with a relatively small sample size excluding older adults. It is still unclear whether or not the findings still hold true when measured subjectively with a larger and more diverse sample size, such as an online survey using a crowdsourcing approach (Huang et al., 2022). This may help to ensure the usability and accessibility of the takeover requests, which is particularly important for older adults given that they are one of the population groups that could benefit from automated vehicles the most (Young et al., 2017). Therefore, this study aims to use a crowdsourcing survey to examine user preferences for location and information formats of vibrotactile displays during takeovers among younger and older drivers.

A national survey was conducted on Qualtrics™ using the crowdsourcing platform Prolific. The study employed a 2 (information formats: informative vs. instructional) × 2 (locations: seat back vs. seat pan) × 2 (age groups: younger vs. older) full factorial design. The survey collected 353 valid responses, including 173 younger (mean age = 32.68) and 180 older (mean age = 69.4) adults. During the survey, vibrotactile displays, which were designed based on four generic AV operation takeover scenarios (a pedestrian crossing ahead, a vehicle speeding, a vehicle too slow blocking the lane, and a construction zone ahead), were presented in video formats. The participants were required to rate them on four themes which were adopted from Petermeijer et al. (2017): (1) Ease of Use, (2) Annoyance, (3) Intention to Use, and (4) Perceived Urgency using a 5-point (1–5) Likert scale.

Results showed that, among the four themes, informative signals only had statistically significantly higher Ease of Use scores than instructional signals. Also, the seat back had higher subjective ratings than the seat pan, reflected by the scores of all four themes. Finally, older adults had higher Perceived Urgency scores than younger adults, but no differences were found in other themes. These findings provide a preliminary understanding of the vibrotactile display information formats and locations, which will contribute to the design of future human-machine interface studies and next-generation in-vehicle display designs.