Generating natural embodied conversational agents within virtual spaces crucially depends on speech sounds and their directionality. In this work, we simulated directional filters to not only add directionality, but also directionally adapt each phoneme. We therefore mimic reality where changing mouth shapes have an influence on the directional propagation of sound. We conducted a study (n = 32) evaluating naturalism ratings, preference and distinguishability of omnidirectional speech auralization compared to static and dynamic, phoneme-dependent directivities. The results indicated that participants cannot distinguish dynamic from static directivity. Furthermore, participants' preference ratings aligned with their naturalism ratings. There was no unanimity, however, with regards to which auralization is the most natural.

This paper explores how na?ve observers recognize and interpret transitive actions (actions involving manipulation of objects) without accompanying speech, in order to derive guidelines for the design of gesture interpretation systems. Semi-structured interviews with 11 observers, interpreting 106 video clips of transitive actions elicited unstaged from 16 participants, reveal that people are generally able to interpret the transitive action as well as characteristics of the object manipulated despite individual variations in how people naturally gesture. In particular, people focus primarily on hand movement and hand shape to correctly interpret object characteristics, and on manner of movement of arms and/or final location of hands to interpret the goal of the transitive action (e.g., arrange objects vs. clear objects). These findings provide insights on aspects of gestures one can focus on to inform and guide the design of gesture interpretation models for interfaces that allow for individual variations in natural gesture production.

This paper explores how interaction with systems using touchless gestures can be made intuitive and natural. Analysis of 912 video clips of gesture production from a user study of 16 subjects communicating transitive actions (manipulation of objects with or without external tools) indicated that 1) dynamic pantomimic gestures where imagined tool/object is explicitly held are performed more intuitively and easily than gestures where a body part is used to represent the tool/object or compared to static hand poses and 2) gesturing while communicating the transitive action as how the user habitually performs the action (pantomimic action) is perceived to be easier and more natural than gesturing while communicating it as an instruction. These findings provide guidelines for the characteristics of gestures and user mental models one must consciously be concerned with when designing and implementing gesture vocabularies of touchless interaction.