FIG. 8.

(Color online) LiFU delivers controlled force to the otolithic mass. (A) 5 MHz LiFU transducer immersed in water and focused on the air-water interface generates a radiation force on the surface. (B) Higher power generates ∼1 mm diameter streaming fountain. (C) Saccular otoliths were excised, suspended using a calibrated elastic wire, and exposed to continuous wave LiFU. Force was measured as a function of stimulus voltage. Force increased as the square of the voltage and was converted to “G” using the otolith mass and acceleration of gravity ($G=F/mg$). (D) cwLiFU was applied to a portion of the excised labyrinth containing the horizontal canal ampulla (HC), anterior canal ampulla (AC), and utricular macula (U). (E) Force was measured with a calibrated elastic wire (W) on isolated saccular otolith (S), U+HC+AC portion of the membranous labyrinth, and on the HC+AC portion of the labyrinth after removal of the utricular otolith. Force was greatly reduced after removal of the utricular otolith, demonstrating that LiFU generates force primarily by reflection off the otolithic mass, and not by absorption.