Externalization of sounds with non-individualized head-related transfer functions and without visual information

A sound produced by a real source is perceived as “externalized,” i.e., outside the head, meaning that it is part of the sound environment of the listener. Conversely, when listening to sounds over headphones, they are generally perceived as “internalized,” i.e., inside the head. In the framework of a research project dealing with the evaluation of comatose patients using sounds reproduced over headphones, it is aimed to investigate the influence of the realism of auditory stimulation through some degree of externalization. Experiments were conducted with non-patients (normal-hearing, awake) while conserving the constraints related to the clinical evaluation (non-individualized head-related transfer functions and no visual reference). A first experiment investigated sound externalization using four types of signals (pink noise, music, speech, and bottles clinging) convolved with different non-individualized binaural room impulse responses measured at different azimuths in different rooms. Diotic reference...