Supplementary data for the paper 'Should an External Human-Machine Interface Flash or Just Show Text? A Study with a Gaze-Contingent Setup'

Automated vehicles need to prioritize pedestrian safety. One way to achieve this is through external human-machine interfaces (eHMIs) that send visual signals to pedestrians. eHMIs can be either text-based or light-based. However, there has been limited research on the effects of these types of eHMI on human information processing and attention allocation. This study aimed to fill this gap by using a gaze-contingent approach, which blurs the view outside a circular aperture, to test the hypothesis that text-based eHMIs, which require focused or foveal attention, result in longer response times compared to light-based eHMIs, which can be understood using peripheral vision. In this study, 23 participants watched animated video clips of traffic situations involving automated vehicles with either no eHMI, a flashing-light eHMI, or a text-based eHMI. Their eye movements were tracked, and they were asked to press the spacebar when they felt it was safe to cross the road. The results showed faster response times when an eHMI was present, with no significant difference between the two types of eHMIs. Further analysis suggested that the flashing-light eHMI captured attention briefly, while the text-based eHMI held attention for a longer period. When no eHMI was present, participants focused on the approaching vehicle for the longest time. The gaze-contingent window resulted in fewer eye movements and slower response times. In conclusion, the study showed that the gaze-contingent window negatively affected response times and eye movements, emphasizing the importance of considering peripheral vision when designing eHMIs for pedestrian safety.

自动驾驶车辆需将行人安全置于优先地位，实现这一目标的途径之一是通过向行人传递视觉信号的外部人机交互界面（external human-machine interfaces，eHMIs）。eHMIs可分为基于文本类与基于灯光类两类。然而，目前针对这两类eHMI对人类信息处理与注意力分配的影响相关研究仍较为匮乏。本研究采用注视依存范式——该范式会模糊圆形视窗以外的视野——来验证如下假说：相较于可通过周边视觉识别的基于灯光类eHMI，需集中注意力或中央凹视觉参与的基于文本类eHMI会导致更长的反应时。本研究共招募23名被试，让其观看包含自动驾驶车辆的交通场景动画视频片段，这些车辆分别搭载无eHMI、闪烁灯光eHMI或基于文本类eHMI。研究过程中追踪被试的眼动轨迹，并要求被试在认为可安全横穿马路时按下空格键。结果显示，当车辆搭载eHMI时，被试的反应时更短，且两类eHMI对应的反应时无显著差异。进一步分析表明，闪烁灯光eHMI仅能短暂吸引注意力，而基于文本类eHMI则可更长时间维持注意力；当未搭载eHMI时，被试对驶来车辆的注视时长最长。注视依存视窗会减少眼动次数并延长反应时。综上，本研究证实注视依存视窗会对反应时与眼动产生负面影响，这凸显了在面向行人安全的eHMI设计中，考量周边视觉因素的重要性。