## 2 Design and Hypothesis  
This study aims to examine auditory spatial attention and sound localization ability of children and adolescents with ASD within a multi-modal virtual reality game environment. The therapeutic outcomes of VR interventions often rely on the immersion of the participant through place illusion [53]. This is particularly important when designing virtual interventions for individuals with autism [11], a population who have difficulties in generalizing newly skills to real-world applications. By conducting investigations within a VR environment similar to which participants may experience within an intervention setting, test parameters may be precisely controlled whilst the user interactions and behavioral models can be robustly recorded. Furthermore, the inclusion of dynamic visuals and game mechanics maintains participant immersion, therefore examining a pattern of behavior closer to that within a conventional virtual reality experience removed from experimental conditions [54]. Previous work by [PERSON] et al. [55] measured spatial presence within the 'blue room', an advanced collaborative virtual environment (CVE). The room makes use of visual images projected onto four screens located on three walls and the ceiling, with audio being delivered over a surround sound loudspeaker system. The paper reported that children with ASD showed equal amounts of attention to the virtual content than healthy controls and engaged with the virtual environment requirements. However, loudspeaker-based systems are often less effective at simulating the necessary ITD and ILD cues needed for three-dimensional spatial audio reproduction. Speaker crosstalk causes significant signal interference between each speaker and the opposite ear of the listener, resulting in impaired localization performance [56]. In contrast, head-track headphone-based systems are more successful at recreating dynamic soundfields which respond to the listeners position within the virtual world [36].  
This investigation followed an in-between subject design. Participants were randomly allocated to either a 3D spatial audio, or control group. The 3D audio group would be exposed to spatial audio reproduced binaurally over headphones. The control group would listen to a monaural representation of the virtual auditory scene presented to both ears over headphones. Each participant group completed a two-phase experiment which first tested spatial audio attention, followed by a sound localization task. Both within a multi-modal virtual reality environment (see Figure 3).  
It is hypothesized that subjects exposed to binaural-based spatial audio would show more spatial attention to auditory stimuli compared with the mono sound control group, indexed through more precise head orientation towards the presented audio targets. Furthermore, spatial audio stimuli would influence participant positional movement with the virtual environment. Additionally, based on previous studies of auditory scene analysis deficits in ASD, it is predicted that localization times will be higher for audio cues with the most amount of competing environmental background noise. Finally, by examining spatial attention towards complex speech and non-speech sounds, it is possible to investigate if differences in spatial auditory attention are the consequence of a reduced orientation towards social stimuli.