通过对流动起伏的时域和空域分析获测量流动速度和流动方向
If exposed to bulk water flow, fish lateral line afferents respond only to flow fluctuations (AC) and not to the steady (DC) component of theflow. Consequently, a single lateral line afferent can encode neither bulk flow direction nor velocity. It is possible, however, for a fish toobtain bulk flow information using multiple afferents that respond only to flow fluctuations. We show by means of particle imagevelocimetry that, if a flow contains fluctuations, these fluctuations propagate with the flow.Across-correlation of water motion measuredat an upstream point with that at a downstream point can then provide information about flow velocity and flow direction. In this study,we recorded from pairs of primary lateral line afferents while a fish was exposed to either bulk water flow, or to the water motion causedby a moving object.Weconfirm that lateral line afferents responded to the flow fluctuations and not to theDCcomponent of the flow, andthat responses of many fiber pairs were highly correlated, if they were time-shifted to correct for gross flow velocity and gross flowdirection. To prove that a cross-correlation mechanism can be used to retrieve the information about gross flow velocity and direction, wemeasured the flow-induced bending motions of two flexible micropillars separated in a downstream direction. A cross-correlation of thebending motions of these micropillars did indeed produce an accurate estimate of the velocity vector along the direction of themicropillars.