  We studied the influence of mechanical vibrotactile signals in the acoustic
range to the visual perception of flickering images. These images are shown on
a CRT screen intermittent at about 75 Hz, without external perturbations are
perceived as constant and stable. However, if presented together with a
controlled acoustical vibration an illusion is perceived. The images appears to
float out of the screen, while the rest of the room is still perceived
normally. The acoustical signal given to the subjects were of very low
frequency (below 100Hz) and low amplitude (almost inaudible). The stimuli were
transmitted through direct contact to the subject's chin with the use of a
plastic stick connected to a speaker. The nature of the illusion is described
and a basic theoretical model is given.
