Auditory interfaces offer a solution to the problem of effective eyes-free mobile interactions. However, a problem with audio, as opposed to visual displays, is dealing with multiple simultaneous information streams. Spatial audio can be used to differentiate between different streams by locating them into separate spatial auditory streams. In this thesis, we consider which spatial audio designs might be the most effective for supporting multiple auditory streams and the impact such spatialisation might have on the users' cognitive load.
An investigation is carried out to explore the extent to which 3D audio can be effectively incorporated into mobile auditory interfaces to offer users eyes-free interaction for both multitasking and accessing location-based information. Following a successful calibration of the 3D audio controls on the mobile device of choice for this work (the Nokia N95 8GB), a systematic evaluationof 3D audio techniques is reported in the experimental chapters of this thesis which considered the effects of multitasking, multi-level displays, as well as differences between egocentric and exocentric designs.
One experiment investigates the implementation and evaluation of a number of different spatial (egocentric) and non-spatial audio techniques for supporting eyes-free mobile multitasking that included spatial minimisation. The efficiency and usability of these techniques was evaluated under varying cognitive load. This evaluation showed an
important interaction between cognitive load and the method used to present multiple auditory streams. The spatial minimisation technique offered an effective means of presenting and interacting with multiple auditory streams simultaneously in a selective-attention task (low cognitive load) but it was not as effective in a divided-attention
task (high cognitive load), in which the interaction benefited significantly from the interruption of one of the stream.
Two further experiments examine a location-based approach to
supporting multiple information streams in a realistic eyes-free mobile environment. An initial case study was conducted in an outdoor mobile audio-augmented exploratory environment that allowed for the analysis and description of user behaviour in a purely exploratory environment. 3D audio was found to be an effective technique to disambiguate multiple sound sources in a mobile exploratory
environment and to provide a more engaging and immersive experience as well as encouraging an exploratory behaviour. A second study extended the work of the previous case study by evaluating a number of complex multi-level spatial auditory displays that enabled interaction with multiple location-based information in an indoor mobile audio-augmented exploratory environment. It was found that a consistent exocentric design across levels failed to reduce workload or increase user satisfaction, so this design was widely rejected by users. However, the rest of spatial auditory displays tested in this study encouraged an exploratory behaviour similar to that described in the previous case study, here further characterised by increased user satisfaction and low perceived workload
