Daly-Jones, O., Monk, A., and Watts, L. Some advantages of video conferencing over high-quality audio conferencing: fluency and awareness of attentional focus. Int. J. Hum.-Comput. Stud. 49, 1 (1998), 21–58. [pdf]
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This article does a great job in summarizing the work that at that time was relevant for video-mediated communication. The authors list four pragmatic needs that must be fulfilled through the transmission of auditory or visual information in human interaction: making contact; allocating turns; monitor understanding and attention and finally supporting deixis. The authors list useful resources for each of these needs.
The article describes how deixis is interrelated with eye-gaze and the value of visual data for collaborative work. The the article resumes the results in studies showing the impact of different video-communication technologies on distance collaboration summarizing that video mediation does not deliver the same benefits of face-to-face interaction.
The study reports an experimental setup where the authors compared two experimental conditions full audio and full video interaction. They conclude that the utility of a certain media should be considered with regard to the task.
Audio information is a sufficiently rich resource when it comes to coordinating fluent conversations. However the lack of video was found problematic for small groups resulting in less fluent communication.