Fig. 3. A representative measurement of the flexural stiffness of a superficial neuromast. (A) Each stiffness measurement was calculated from measurements of the position of the fiber tip (x_tip, purple) and fiber base (x_base, green) of the glass fiber when pressed against a cupula. Noise was filtered from the raw data (light lines) to yield the position measurements used in the calculation (dark lines). (B) The filtered position data (solid black line) were used to calculate the stiffness of the cupula. The slope of a linear curve fitted to these data (gray line, m=0.440) yielded a flexural stiffness for the cupula [(EI)_cup=2.28x10^–20 N m²] using Eqn 3. A slope equal to unity (dashed line, m=1) represents the relationship predicted for a completely compliant neuromast. (C) The positional changes from B provide the basis for the calculation of the deflection of the cupulae and the force exerted by the fiber to cause that deflection.