Loudness constancy for noise and speech: How instructions and source information affect loudness of distant sounds.

The physical properties of a sound evolve when traveling away from its source. As an example, the sound pressure level at the listener's ears will vary according to their respective distance and azimuth. However, several studies have reported loudness to remain constant when varying the distance between the source and the listener. This loudness constancy has been reported to occur when the listener focused attention on the sound as emitted by the source (namely the distal stimulus). Instead, the listener can focus on the sound as reaching the ears (namely the proximal stimulus). The instructions given to the listener when assessing loudness can drive focus toward the proximal or distal stimulus. However, focusing on the distal stimulus requires to have sufficient information about the sound source, which could be provided by either the environment or by the stimulus itself. The present study gathers three experiments designed to assess loudness when driving listeners' focus toward the proximal or distal stimuli. Listeners were provided with different quality and quantity of information about the source depending on the environment (visible or hidden sources, free field or reverberant rooms) and on the stimulus itself (noise or speech). The results show that listeners reported constant loudness when asked to focus on the distal stimulus only, provided enough information about the source was available. These results highlight that loudness relies on the way the listener focuses on the stimuli and emphasize the importance of the instructions that are given in loudness studies.