Hands are the most important tool to interact with virtual environments, and they should be available to perform the most critical tasks. For example, a surgeon in VR should keep his/her hands on the instruments and be able to do secondary tasks without performing a disruptive event to the operative task. In this common scenario, one can observe that hands are not available for interaction. The goal of this systematic review is to survey the literature and identify which hands-free interfaces are used, the performed interaction tasks, what metrics are used for interface evaluation, and the results of such evaluations. From 79 studies that met the eligibility criteria, the voice is the most studied interface, followed by the eye and head gaze. Some novel interfaces were brain interfaces and face expressions. System control and selection represent most of the interaction tasks studied and most studies evaluate interfaces for usability. Despite the best interface depending on the task and study, the voice was found to be versatile and showed good results amongst the studies. More research is recommended to improve the practical use of the interfaces and to evaluate the interfaces more formally.

中文翻译：

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沉浸式虚拟现实中的免提交互：系统评价

手是与虚拟环境交互的最重要工具，应该可以用来执行最关键的任务。例如，VR 中的外科医生应该把手放在器械上，并能够执行次要任务，而不会对手术任务造成破坏性事件。在这种常见场景中，可以观察到手不可用于交互。本系统评价的目标是调查文献并确定使用了哪些免提界面、执行的交互任务、界面评估使用的指标以及此类评估的结果。在符合资格标准的 79 项研究中，声音是研究最多的界面，其次是眼睛和头部凝视。一些新颖的界面是大脑界面和面部表情。系统控制和选择代表了研究的大部分交互任务，大多数研究评估了界面的可用性。尽管最好的界面取决于任务和研究，但发现语音是通用的，并且在研究中显示出良好的结果。建议进行更多研究以改进接口的实际使用并更正式地评估接口。