Abstract
In order to survive, animals must quickly and accurately locate prey, predators, and conspecifics using the signals they generate. The signal source location can be estimated using multiple detectors and the inverse relationship between the received signal intensity (RSI) and the distance, but difficulty of the source localization increases if there is an additional dependence on the orientation of a signal source. In such cases, the signal source could be approximated as an ideal dipole for simplification. Based on a theoretical model, the RSI can be directly predicted from a known dipole location; but estimating a dipole location from RSIs has no direct analytical solution. Here, we propose an efficient solution to the dipole localization problem by using a lookup table (LUT) to store RSIs predicted by our theoretically derived dipole model at many possible dipole positions and orientations. For a given set of RSIs measured at multiple detectors, our algorithm found a dipole location having the closest matching normalized RSIs from the LUT, and further refined the location at higher resolution. Studying the natural behavior of weakly electric fish (WEF) requires efficiently computing their location and the temporal pattern of their electric signals over extended periods. Our dipole localization method was successfully applied to track single or multiple freely swimming WEF in shallow water in real-time, as each fish could be closely approximated by an ideal current dipole in two dimensions. Our optimized search algorithm found the animal’s positions, orientations, and tail-bending angles quickly and accurately under various conditions, without the need for calibrating individual-specific parameters. Our dipole localization method is directly applicable to studying the role of active sensing during spatial navigation, or social interactions between multiple WEF. Furthermore, our method could be extended to other application areas involving dipole source localization.
Highlights
Animals must accurately locate signal sources of various kinds [1,2,3,4,5], since this allows animals to quickly respond to prey, predators, or potential mate signals that are very important for their survival
We propose a dipole localization method based on the lookup table (LUT) operation, which compares actual received signal intensities from multiple recording channels with theoretically predicted signal intensities at many possible dipole locations
The measured received signal intensities (RSI) values were compared with the theoretical values computed by the two-dimensional ideal dipole model (Fig. 1C) at many possible dipole locations, and the closest matching location was found by our search algorithm (Fig. 1D)
Summary
Animals must accurately locate signal sources of various kinds [1,2,3,4,5], since this allows animals to quickly respond to prey, predators, or potential mate signals that are very important for their survival. Many biological and non-biological systems can determine signal locations on the basis of comparing received signal intensities (RSI) from two or more spatially distributed sensors [2,6,7,8]. The signal localization task becomes more complex if the RSI depends on the orientation of the signal source, such as the signals dependent on the orientation of an electric fish dipole. A current dipole consists of two physically separated current sources having opposite polarities, which creates spatially non-uniform field strength as a function of distance and orientation. Weakly electric fish species can locate other member of species using the electric field they generate [12,13,14,15,16]
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