We identify usability challenges facing consumers adopting Virtual Reality (VR) head-mounted displays (HMDs) in a survey of 108 VR HMD users. Users reported significant issues in interacting with, and being aware of their real-world context when using a HMD. Building upon existing work on blending real and virtual environments, we performed three design studies to address these usability concerns. In a typing study, we show that augmenting VR with a view of reality significantly corrected the performance impairment of typing in VR. We then investigated how much reality should be incorporated and when, so as to preserve users' sense of presence in VR. For interaction with objects and peripherals, we found that selectively presenting reality as users engaged with it was optimal in terms of performance and users' sense of presence. Finally, we investigated how this selective, engagement-dependent approach could be applied in social environments, to support the user's awareness of the proximity and presence of others.

This paper contributes novel measures of user engagement in mobile music retrieval, linking these to work in music psychology, and illustrating resulting design guidelines in a demonstrator system. The large music collections available to users today can be overwhelming in mobile settings, they offer 'too-much-choice' to users, who often resort to shuffle-based playback. Work in music psychology has introduced the concept of music engagement -- listeners vary in their desired control over their music listening, and engagement varies with listening context. We develop a series of metrics to capture music listening behaviour from users' interaction logs. In a survey of 94 music listeners, we show significant correlations between music engagement from questionnaires and the presented quantitative metrics. We show how music retrieval can adapt to this engagement, developing a tablet-based demonstrator system, with an exploratory evaluation.

A novel investigation of pressure input is presented where it is characterised as a transient modality, one that has a natural inverse, bounce-back and a state that only persists during interaction. Three empirical studies are described that evaluate pressure for use as a non-dominant hand input modality, where the ability to target and maintain pressure while simultaneously performing a dominant-hand targeting task is investigated. Pressure accuracy was high (93%) and the impact on dominant-hand targeting was low. Mean pressure accuracy when selecting targets by releasing pressure was also high (89%) as was selecting targets by applying pressure from a non-zero starting point (94.4%). The ability to accurately maintain pressure over time was better with larger target pressures. Example applications and design guidelines are presented that enable designers to exploit the transient properties of pressure input in interaction design.

A novel interaction style is presented, allowing in-pocket music selection by tapping a song's rhythm on a device's touchscreen or body. We introduce the use of rhythmic queries for music retrieval, employing a trained generative model to improve query recognition. We identify rhythm as a fundamental feature of music which can be reproduced easily by listeners, making it an effective and simple interaction technique for retrieving music. We observe that users vary in which instruments they entrain with and our work is the first to model such variability. An experiment was performed, showing that after training the generative model, retrieval performance improved two-fold. All rhythmic queries returned a highly ranked result with the trained generative model, compared with 47% using existing methods. We conclude that generative models of subjective user queries can yield significant performance gains for music retrieval and enable novel interaction techniques such as rhythmic filtering.

We describe an approach to improving the design and development of Brain-Computer Interface (BCI) applications by simulating the error-prone characteristics and subjective feel of electroencephalogram (EEG), motor-imagery based BCIs. BCIs have the potential to enhance the quality of life of people who are severely disabled, but it is often time-consuming to test and develop the systems. Simulation of BCI characteristics allows developers to rapidly test design options, and gain both subjective and quantitative insight into expected behaviour without using an EEG cap. A further motivation for the use of simulation is that 'impairing' a person without motor disabilities in a game with a disabled BCI user can create a level playing field and help carers empathise with BCI users. We demonstrate a use of the simulator in controlling a game of Brain Pong.