# Head-Related Transfer Functions for Dynamic Listeners in Virtual Reality
## 6 Discussion
### Dynamic Results  
The lack of significant differences between the individual and generic HRTFs in dynamic localization accuracy and overall audio quality in the 6-DoF VR experiment supports our fourth hypothesis regarding the similarity of the HRTFs in this setting. This finding is corroborated by previous research in dynamic localization, where there are often no differences found between individual and generic HRTFs [5, 8]. However, a few recent studies also show the contrary. [PERSON] et al. [12] utilized a constricted movement range where head rotations were allowed, but the sound playback would stop outside of the range. The audio targets were placed beyond the allowed movement range so that dynamic cues could be incorporated in the localization process, but the localization accuracy could be tested for source directions other than only in front. [PERSON] et al. [12] found a significant localization improvement with individual HRTFs over generic HRTFs, which is in contrast to the findings of our study. Their experimental setup did not provide visual cues or motor cues beyond the limited movement range, possibly explaining part of the differences. Another study using audio-visual VR showed that individual HRTFs were preferred in localizability and realism over a generic HRTF set when a target object was a drone flying overhead along the sagittal plane in a pre-programmed animation [13]. This finding is in contrast to our dynamic experiment results. One reason for the contrasting results could be the dynamic audio object and seated participant employed by [PERSON] and [PERSON] [13] in contrast to emphasizing the movement of the listener. A dynamically moving audio-visual object has been found to reduce listener movement in 6-DoF VR audio quality evaluations [42], which might lessen the adaptation to generic HRTF cues, but this assertion will require further studies. The lack of perceptual differences in dynamic localization accuracy is surprising, keeping in mind the different number of measurement points in the individual sets (\(Q=4608\)) compared to the generic set (\(Q=1550\)). The difference stems from the elevation resolution since the azimuth resolution was the same for all sets (\(5^{\circ}\)). In the localization scene with the audio object in the scene at 1.5 m height, even the _Generic Horizontal_ condition with \(Q=72\) measurement points could not be statistically differentiated from the _Generic_ set or the _Modeled_ set, further highlighting the strength of visual influence on auditory localization. On another note, in dynamic localization without visual cues, a sparse HRTF set with just \(Q=36\) measurement points covering the whole sphere combined with linear interpolation for intermediate locations was shown to yield comparable localization accuracy with a high-resolution HRTF set with \(Q=612\)[12]. Our experiments did not employ an interpolation strategy, which might reduce possible differences between the HRTF sets with different numbers of measurement points. Using the 100-point localization accuracy scale with intermediate quality labels, the individual and spherical generic HRTF sets were evaluated in the _good_ (60-80 points) and _excellent_ (80-100 points) localizability range. Although the HRTF sets are to some extent affecting each others' relative scores in the absence of an auditory reference, it may be assumed that the visual and motor cues provided sufficient reference conditions for an absolute judgment of the localization accuracy for the experienced listeners in our experiments. This result adds confidence that the sound delivery chain comprising the diffuse-field equalization of the HRTFs and headphones, can convey a convincing spatial impression.