DIPOLE SOURCE LOCALIZATION BY THE MOTTLED SCULPIN .2. THE ROLE OF LATERAL-LINE EXCITATION PATTERNS

Extracellular, single unit recording techniques were used to measure t he responses of posterior lateral line nerve fibers to a 50-Hz dipole source that slowly changed its location along the length of the fish. The flow-field equations for a dipole source were used to model the pr essure gradient pattern and thus, the expected excitation pattern alon g a linear array of lateral line receptor organs for different source locations. Finally, excitation patterns were similarly modeled along t he left and right side of the fish's head for actual steps taken by sc ulpin in approach pathways to the 50-Hz dipole source. Spatial histogr ams of posterior lateral line nerve fiber responses to different locat ions of the dipole source could be predicted from pressure gradient pa tterns modeled from the flow-field equations, confirming that the mode ling approach applied to behavioral results was a good predictor of ex citation patterns likely to be encoded by the lateral line periphery. An examination of how modeled excitation patterns changed from one pos ition to the next in typical approach pathways and how patterns differ ed between positions from which successful and unsuccessful strikes we re launched suggests that approach and strike strategies can indeed be explained by the information available in excitation patterns. In par ticular, changes in the spatial distribution of pressure gradient dire ctions (polarities), available only when the source is lateral (as opp osed to directly in front of the fish), appear to enhance the ability of sculpin to determine source distance. Without such information, mis ses are more likely to occur and successful strikes are more likely to be launched from short distances only.