External Human-Machine Interfaces (eHMIs) have been proposed to enhance communication between automated vehicles (AVs) and pedestrians, with growing interest in multi-modal designs such as audio-visual eHMIs. Just as poor lighting can impair visual cues, a loud background noise may mask the auditory stimuli. However, its effects within these systems have not been examined, and little is known about how pedestrians -- particularly Deaf and Hard-of-Hearing (DHH) people -- perceive different types of auditory stimuli. We conducted a virtual reality study (Hearing N=25, DHH N=11) to examine the effects of background noise (quiet and loud) on auditory stimuli (baseline, bell, speech) within an audio-visual eHMI. Results revealed that: (1) Crossing experiences of DHH pedestrians significantly differ from Hearing pedestrians. (2) Loud background noise adversely affects pedestrians' crossing experiences. (3) Providing an additional auditory eHMI (bell/speech) improves crossing experiences. We outlined four practical implications for future eHMI design and research.

翻译：外部人机界面（eHMIs）被提出用于增强自动驾驶车辆（AVs）与行人之间的通信，其中视听融合的多模态设计日益受到关注。正如不良照明会削弱视觉信号，高强度背景噪声也可能掩蔽听觉刺激。然而，此类系统中背景噪声的影响尚未得到充分研究，且行人——特别是聋哑及听力障碍（DHH）人群——对不同类型听觉刺激的感知机制仍不明确。本研究通过虚拟现实实验（听力正常者N=25，DHH人群N=11）探究了视听eHMI中背景噪声（安静/嘈杂）对听觉刺激（基线状态、铃声、语音）的影响。结果显示：（1）DHH行人的道路穿越体验与听力正常者存在显著差异；（2）高强度背景噪声对行人穿越体验产生负面影响；（3）提供附加听觉eHMI（铃声/语音）能改善穿越体验。基于此，我们为未来eHMI设计与研究提出了四项实践指导原则。