## Human-Performed Classification
### Listening Test Results  
In total, all the listeners made 6360 classifications (212 listeners \(\times\) 30 classifications). The listening test results were analyzed in terms of the classification \"accuracy,\" defined as the percentage ratio of the correct classifications to the total number of classifications made. As a correct classification, we considered a case whereby, for a given stimulus, the scene designated by a listener matched the intended scene during its binaural synthesis. We deliberately used the term \"intended\" instead of \"actual\" as, ultimately, it is the listeners who decide how the scenes are perceived. According to the raw results, the overall classification rate exhibited by the listeners was low, being equal to 40.6%. This outcome is only slightly greater than the no-information rate (an accuracy level resulting from classifying the scenes by chance), which in our experiment amounted to 33.3%. This was an unsurprising outcome, since front-back discrimination, involved during the scene classification, is a challenging task under the static head scenario and also considering all the confounding electro-acoustical factors, including uncontrolled background noise, uncontrolled headphones frequency response, and no free-field headphone compensation. Nevertheless, due to a large number of classifications made, the above result is statistically significant at \(p=10^{-33}\) level according to the binomial test. The confusion matrix obtained for the raw data is shown in Figure 2a. It confirms the erratic nature of the results, with the accuracy levels along a diagonal axis only slightly exceeding the no-information rate. Confusion matrices obtained for the stimuli synthesized using individual BRIR sets are quantitatively similar to the above one. Therefore, for clarity, the confusion matrices for only three selected BRIR sets (1, 2, and 5) are presented in panels b-d of that figure. In contrast to the above results, the confusion matrix obtained for BRIR set 13 appeared to be slightly different. This is presented in panel e. Visual inspection of that matrix indicates that the listeners tended to misclassify _BF_ scenes as _FB_ and _FF_ scenes as _BF_. This unusual effect was also confirmed later in the statistical post-hoc test accompanying the analysis of variance (see below). The accuracy scores were also calculated for each listener and inspected in the form of a histogram presented in Figure 3, showing the distribution of the listeners' accuracy scores. It can be seen that the accuracy of the listeners ranged from 10% to almost 80%. The main peak in the histogram indicates that almost 70 listeners exhibited very poor performance, approximately equal to the no-information rate (33.3%), highlighting the need for some form of post-screening of the data. Another group of approximately 70 listeners (the second peak in the histogram) showed a better classification performance, ranging from 45% to 65%. Low and high statistical significance rate levels, equal to 13.3% and 53.3%, respectively, were also included in the histogram (green vertical lines). They were estimated based on the binomial test performed at a 0.05 significance level. The data from all the listeners whose scores lay between these two rates could not be considered as statistically significant. This does not mean that their data are meaningless, as the statistical significance depends on the number of classifications made and, consequently, when the data from all the listeners are combined, the statistical sensitivity of the experimental protocol substantially increases (as it was already demonstrated above in relation to the classification accuracy from the all listeners). Out of 212 listeners, only 48 had accuracy scores exceeding the high significance rate. The data from these listeners were later retained in the post-screening procedure (see below). Surprisingly, one outlying listener had a score below the low-significance rate, implying that he or she consistently misclassified some scenes.