Figure 1.

Experimental apparatus and task sheet

The experimental set-up. The participant was seated in the middle of a cubic sound-attenuated room with two fingers of both hands placed in two vibrating boxes on the sides of the body (A and B); audio and vibrotactile stimuli were designed to induce perception of objects moving around the space. During the audio condition, sounds were played from speakers mounted on the walls, with the 3D sound environment as a virtual sphere created using 12th order Ambisonics.

(C and D) The participant was given an answer sheet showing 3 possible elevation levels and 8 possible horizontal locations of start and endpoints for each moving trajectory. The task of the participant was to report the start points, the endpoints and the direction of audio, tactile or audio-tactile stimuli.