## 3 Methods
### Stimuli  
**Visual Environment:** The virtual environment used for this experiment represents an enchanted forest setting at night (see Figure 4). It has been noted that when designing visual aspects of virtual reality for ASD applications, the presence of visual clutter significantly affects user performance at completing tasks [58]. Therefore, the graphical environment was designed to be engaging without presenting visual elements that may have driven user attention away from the auditory stimuli. Furthermore, individuals with autism that also exhibit abnormalities in processing visual information can often attempt to avoid visual input such as bright lights [59]. The use of a darker environment reduces the possibility of anxiety related behaviors that are a result over sensory over-stimulation [60].  
**Auditory Stimuli:** Figure 5a,b are overhead views of the virtual environment displaying the auditory stimuli placement and movement area, with a summarization of each audio object in Tables 1 and 2. All stimuli were recorded or edited using Reaper digital audio workstation and WWise [61] game audio engine. Experimental groups were based upon audio rendering techniques. The 3D audio group would listen to binaural-based spatial audio rendered via the Google Resonance spatial audio SDK [62]. Audio was presented at a fixed playback level of 68 dbA. This was matched to a \(-\)20 dBFS RMS value of a pink noise test signal playing at a distance of 1m from the listener.  
_Phase One:_ Eight spatial auditory events (see Table 1) were placed in the VE. All audio events were stationary with the exception of event 7 which moved around the entire environment over the course of 30 s. Previous research conducted by the authors has noted that target stimuli among competing audio could prompt negative effects on auditory spatial attention within VR environments for individuals with ASD [63]. This is further supported by research that reports within competing background noise, those with autism often display difficulties in separating relevant auditory information (i.e., speech and target noises) into discrete auditory objects connected to the different sound sources within the environment [42]. To minimize the effects of any complications in auditory scene analysis associated with ASD, environmental audio was reduced to \(-\)43 LUFS while each Phase One event was rendered.  
_Phase Two:_ Eight spatial audio events representing virtual characters were placed throughout the VE. In terms of type, audio stimuli were divided into simple and social types. Simple stimuli consisted of a bell sound effect, with the social stimuli representing a speech-like sound. All events were stationary except for movement towards the player once the character was found.  
A spatialized composite background audio track was provided which was derived from several discrete auditory objects placed throughout the VE, matching the visual scene. This included sounds representing wind, water, frogs, birds, crickets and wind chimes.  
Figure 4: Visual Environment—360 degree capture.  
The level of the background sounds was either \(\geq\)\(-\)43 LUFS or \(\geq\)\(-\)53 LUFS. These levels were taken from a past study that evaluated the effects of background noise on spatial attention in VE's with participants with ASD [63]. Using an audio object-based hierarchical model based on a simplified technique designed by [PERSON] et al. [64] to increase the accessibility of complex audio content for those with hearing impairments. Background audio levels would be reduced by removing the bird, cricket, and wind chime ambient sound objects; the aim of this process is to maintain participant immersion.  
To further investigate auditory detection in noise, target stimuli were played at differing signal-to-noise ratio (SNR). For auditory events with +10 SNR, the stimulus level would be 10 LUFS higher than the background noise level. For auditory events with 0 SNR, the stimulus would be set at an equal level to that of the background noise.