## 4 Experiment II: Directivity-Controlled Auditory Distance in a Real Room
### Auditory Distance  
Figure 13 shows the results for the distance rating task of the second experiment.  
A pairwise ANOVA of the data reveals the beampattern to be a significant factor for \(A_{2\ldots 4}^{*}\) (\(p\leq 0.02\)). Although medians of the design \(A^{*}\) form a linear curve, the significant range of the first experiment using the design \(A\) in room \(R_{2}\) is not achieved, cf. Figure 7. For design \(B\), significance is attained by directivities \(B_{3\ldots 6}\) (\(p\leq 0.02\)) and for design \(C\) by directivities \(C_{2\ldots 4}\) (\(p\leq 0.01\)).  
Although comparisons of these results with significances of the first experiment shown in Figure 4 should be interpreted with caution, indications are found that the IKO yields less pronounced distance impressions. Even with design \(D\), corresponding to a combination of directivities that should yield the most pronounced effect, not more then 4 significantly different distances are obtained (\(D_{2\ldots 5}\), \(p\leq 0.01\)).  
Medians of design \(B\) remain sigmoid-shaped as they are in the first experiment, whereas medians obtained by design \(C\) show major differences. While simulated conditions \(C_{3\ldots 6}\) of the first experiment created significantly different impressions that are localized more distant compared to \(C_{7}\), they are either localized closer to \(C_{7}\), e.g., \(C_{3}\), or are no longer significantly different (\(C_{4\ldots 6}\), \(p\geq 0.17\)) when auralized with the IKO. Informal notes of listeners indicate that the spectral coloration of some conditions led to an impression as if the auditory object is right behind the IKO and the incoming sound is filtered due to acoustic shadowing. Similarly to the first experiment these conditions yield major intersubjective differences as indicated by the size of the 95% confidence intervals.  
If we take a look at the measured beampattern \(C_{3}\) in Figure 11h we find evidence that shifted results can be explained rather by the spectrum of the IKO into the listener's direction as the image source behind the IKO (180\({}^{\circ}\)) receives highly attenuated signals and the direct sound has a low-pass character (400 Hz).  
Figure 13: Experimental results of the distance task for signal \(S_{1}\) and room \(R_{2}\) with use of the IKO.  
Visual cues could explain the less pronounced ratings for large distances, because responses of most listeners (7/10) are within the feasible space limited by the wall at approximately 5 m, leading to a high response frequency in the interval right in front of the wall, cf. Figure 13b.  
The high frequency of responses within the interval of the IKO are due to another effect caused by visual cues. Studies could show that seeing only one possible sound source biases the perceived distance towards it, e.g., [28].  
Interestingly, in the first experiment visual cues were available similarly, but no influence thereof was obtained. Therefore we conclude that in the laboratory environment, in which visual cues do not comply with auditory cues, the former play a minor role. This agrees with findings in [29; 30] showing that sensory interactions, e.g., vision vs. audition, include a weighting process where the most reliable cue contributes the most to the multi-sensory percept.