  A cluster of research in Human-Computer Interaction (HCI) suggests that it is
possible to infer some characteristics of users' mental states by analyzing
electrophysiological responses in real-time. However, it is not clear how to
use the information extracted from electrophysiological signals to create
visual representations of the emotional states of Virtual Reality (VR) users.
Visualization of users' emotions in VR can lead to biofeedback therapies for
training emotion self-regulation. Understanding how to visualize emotions in VR
requires an interdisciplinary approach that integrates disciplines such as
psychology, electrophysiology, and audiovisual design. Therefore, this review
aims to integrate previous studies from these fields to understand how to
develop virtual environments that can automatically create visual
representations of users' emotional states. This manuscript addresses this
challenge in three sections: First, theories related to emotion and affect are
compared. Second, evidence suggesting that specific visual and sound cues tend
to be associated with particular emotions are discussed. And third, some of the
available methods for assessing emotions are described.
