Interpersonal Distance Task - Looming Footsteps Sound Effect

Participants are asked to listen to six audio clips consisting of the sound of footsteps approaching them from the front. In half of the trials, participants are asked to indicate “Stop” when the person heard approaching made them feel uncomfortable with the interpersonal distance. In the other half of the trials, participants were asked to indicate “Stop” when they felt like they could touch the person they heard coming towards them. The order of these two tasks is counterbalanced across participants. In each case, the response times (RT) in milliseconds, i.e. the time taken to indicate “Stop”, is measured, with a longer RT indicating smaller boundaries of space. The task distinguishes between types of peripersonal representations: the former representation being involved in protecting the body, and the latter in goal-directed action. As such, we dissociate between interpersonal and reaching distances. Here we adapted the auditory task by Vagnoni and colleagues (2018) to capture RD to compare with IPD. The walking sound effects were generated and recorded using Unity 3D (Unity Technologies, 2020). Free footstep sounds were downloaded from https://freesound.org/ and were split into single files, one file per footstep. A unity script loaded the footstep audio files when a walking animation was executed and synchronised each sound with the animation. A unity scene with an audio reverb zone was created with a maximum distance of 36 metres. An audio listener was located inside the reverb zone which allowed one to gradually change the footstep sound effect as the animation slowly moved closer to the target. The output was generated using the Unity Recorder tool.

本实验要求参与者聆听六段音频片段，片段内容为从正前方逐步靠近自身的脚步声。在一半的试次中，参与者需在听到靠近者导致其因人际距离（interpersonal distance）不适时，按下“停止”键做出反应；在剩余的另一半试次中，参与者需在认为自身能够触碰迎面走来的发声对象时，按下“停止”键做出反应。两项任务的施测顺序在参与者间进行了平衡处理。两种条件下均会记录参与者按下“停止”键的反应时（response time, RT，单位为毫秒），即完成“停止”反应的耗时；反应时越长，代表个体的空间边界范围越小。该任务可区分两类近体空间表征（peripersonal representations）：前者参与躯体防护相关加工，后者则与目标导向性动作相关。据此，本实验实现了人际距离与伸手可达距离的分离操作。本研究改编自Vagnoni等人（2018）的听觉任务，以测量伸手可达距离（reaching distance, RD），并将其与人际距离（interpersonal distance, IPD）进行对比。脚步声效采用Unity 3D（Unity Technologies, 2020）软件生成并录制；免费脚步声素材从https://freesound.org/网站下载，并被切割为单步脚步声对应的独立音频文件。当触发行走动画时，Unity脚本会加载脚步声音频文件，并将每段音效与动画进行同步匹配。创建了包含音频混响区（audio reverb zone）的Unity场景，混响区最大范围设置为36米；在混响区内放置音频监听器（audio listener），使得当动画角色逐步靠近目标时，脚步声效能够随之发生渐变。最终的实验刺激通过Unity Recorder工具生成。