## 2 Materials and Methods  
### Experimental Setup  
The experimental setup was placed in a dedicated listening room with the dimensions of 10.2 m \(\times\) 7.2 m \(\times\) 3.2 m (L \(\times\) W \(\times\) H) and the volume of 235 m\({}^{3}\). The room is acoustically treated to yield the reverberation time of 0.5 s over the entire standard frequency range of 125 Hz to 4 kHz, except in the 125 Hz octave band, in which the reverberation time is slightly higher and reaches 0.7 s. As the room is also used as a listening room for quality evaluation of sound reproduction systems, the reverberation time measurements were extended to the 63 Hz octave band, in which its value reaches 0.81 s, as well as to 8 kHz octave band, in which it decreases to 0.38 s. The measured noise level in the room was 25 to 30 dBA, depending on the time of day.  
Placing the experimental setup into an anechoic chamber was initially considered and ultimately dismissed, as it does not properly represent the acoustical conditions in a typical home environment and would look and sound unnatural to the test subjects.  
The loudspeakers used in the experiment were a pair of active, bookshelf-sized near-field studio monitors set in a wide stereo configuration. They were put at a distance of 1 m from the listening position. The angle between the loudspeakers was set to 90\({}^{\circ}\) instead of 60\({}^{\circ}\) used in standard stereo listening to facilitate a clear view of the visual stimulus, when used in the experiment. Moreover, this setup allows the sound to be perceived from the direction consistent with the positions of the visual stimulus. The frequency response of the loudspeakers is maintained within \(\pm\)2 dB within the entire frequency range of speech.  
For headphone reproduction, a pair of open headphones, calibrated in terms of frequency response, was used as a part of a dedicated hardware-software package.  
Visual stimulus was used in the experiment to create an illusion of a virtual speaker/interlocutor speaking to the test subject in the listening experiment, and a virtual listener/interlocutor being read to by the test subject in the reading part of the experiment. Due to the SARS-CoV-2 pandemic and all the epidemiological countermeasures that were in force at the time, the decision to use a real person as the visual stimulus had to be abandoned to reduce health risk to a minimum. Instead, a dummy head was appropriately clothed and then put on a small trolley, thus being placed at the height of a standard sitting person. Moreover, the trolley provided an easy way of placing the dummy head at predetermined positions in front of the test subject, or to move it out of sight when no visual stimulus was required. Two positions of the visual stimulus, as viewed from the listener position, are shown in Figure 1.  
Figure 1: Two positions of the visual stimulus in the experiment; left: within the personal space of the subject (at 85 cm); right: within the social space of the subject (at 280 cm).  
To make the execution of the listening part of the experiment as simple as possible for the test subjects, a graphic user interface has been developed using MaxMSP [35] that offers a simple way of changing the level of the currently reproduced sound sample and records the last set value when moving on to the next test sample.  
A class-1 measurement microphone was used in the reading part of the experiment for recording the subjects as they were reading the provided text. The microphone was placed one meter away from the reader.