Latency in a communication system can result in confusing a conversation through loss of causality as people exchange verbal and non-verbal nuances. This paper compares true end-to-end latencies across an immersive virtual environment and a video conference link using the same approach to measure both. Our approach is to measure end-toend latency through filming the movements of a participant and their remote representation through synchronised cameras. We also compare contemporary and traditional immersive display and capture devices, whilst also measuring event latency taken from log files. We compare an immersive collaborative virtual environment to a video conference as both attempt to reproduce different aspects of the face-to-face meeting, the former favouring appearance and the latter attention. Results inform not only the designers of both approaches but also set the requirements for future developments for 3D video which has the potential to faithfully reproduce both appearance and attention.

Social cues, such as eye gaze and pointing fingers, can increase the prioritisation of specific locations for cognitive processing. A previous study using a manual reaching task showed that, although both gaze and pointing cues altered target prioritisation (reaction times [RTs]), only pointing cues affected action execution (trajectory deviations). These differential effects of gaze and pointing cues on action execution could be because the gaze cue was conveyed through a disembodied head; hence, the model lacked the potential for a body part (i.e., hands) to interact with the target. In the present study, the image of a male gaze model, whose gaze direction coincided with two potential target locations, was centrally presented. The model either had his arms and hands extended underneath the potential target locations, indicating the potential to act on the targets (Experiment 1), or had his arms crossed in front of his chest, indicating the absence of potential to act (Experiment 2). Participants reached to a target that followed a nonpredictive gaze cue at one of three stimulus onset asynchronies. RTs and reach trajectories of the movements to cued and uncued targets were analysed. RTs showed a facilitation effect for both experiments, whereas trajectory analysis revealed facilitatory and inhibitory effects, but only in Experiment 1 when the model could potentially act on the targets. The results of this study suggested that when the gaze model had the potential to interact with the cued target location, the model's gaze affected not only target prioritisation but also movement execution.

In this paper we examine how closely together images to be used in 3D reconstruction are captured, when acquisition is started using a software-based trigger delivered to multiple computers on a network. In addition we compare a software triggered pull system to a push system. Synchronisation is a key component in 3D reconstruction systems and can also be one of the most problematic. In a shape-from-silhouette based system, images are captured at the same moment to ensure the position of the object is consistent in all frames. Differences in position between captured frames results in deformations such as holes and missing or extended features. By capturing images of a projected clock, we can tell with around 10ms granularity, how closely together images are captured. This gives us an indication of whether software capture triggers delivered over a network can be used for image acquisition in a 3D reconstruction system, instead of hardware synchronised capture. INTRODUCTIONWhen reconstructing a person in 3D, using a shape from silhouette approach, a number of cameras need to be placed around the individual to provide images for the processing. From these images, usually a silhouette is extracted for use in computing the 3D shape, and the colour information is used in texturing the resultant geometry. This style of 3D reconstruction system allows a reconstruction to be made which can be walked around, and so is useful for situations where people need to collaborate and may be walking around each other. It is typically assumed that camera capture must be synchronised to provide reconstructions of acceptable quality; we investigate whether this really is the case.In this paper, we look at how closely together camera images are captured when a software trigger is delivered to computers over a network. We attempt to find out whether software triggers are an acceptable replacement for more expensive and universally used hardware triggers in 3D reconstruction systems. Our main interest is in 3D telepresence and so we look at how a pull-based system would fit into such an application. 3D telepresence requires realtime operation, with low latency 3D representations delivered to users at acceptable frame rates.In a previous study [Moore et al, 2010] we investigated what effect different levels of capture delay in images had on the output of a 3D reconstruction algorithm. It was found that the reconstruction process was surprisingly tolerant to lack of synchronisation and indicated that it may be possible to create a system without a hardware capture trigger. This experiment had been conducted purely through the use of a simulator.For our investigation we used a system in which a UDP trigger packet was broadcast to all capture computers on the network. These computers then called acquisition on each camera, grabbed the resultant frame and stored it to disk. The captured images were of a millisecond clock projected onto the floor. Frames were then examined to see if the same time was shown in each. As a second part to the ex...

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