Fig. 4. Responses of a type I medial octavolateralis nucleus (MON) unit to a 50 Hz vibrating sphere stimulus in still (left) and running (15.5 cm s^-1; right) water. (Top) Raster plots of the responses to 10 stimulus repetitions for three displacement amplitudes (2717, 890 and 305 µm) (see also Figs 5,6,7,8). The stimulus trace is shown below the rasters. (Bottom) Level-response functions. Evoked discharge rates (means ± S.D.) (filled circles), averaged across 20 stimulus presentations, ongoing discharge rates (open circles) and synchronization coefficients (triangles) are plotted as function of sphere displacement. In still water, this unit responded to the vibrating sphere with an increase in discharge rate. In running water, the unit's ongoing discharge rate was increased. Consequently, the response to the vibrating sphere was masked both in terms of spike rate and phasecoupling.