Strategies of object polarization and their role in electrosensory information gathering

Abstract

Weakly electric fish polarize the nearby environment with a stereotyped electric field and gain information by detecting the changes imposed by objects with tuned sensors. Here we focus on polarization strategies as paradigmatic bioinspiring mechanisms for sensing devices. We begin this research developing a toy model that describes three polarization strategies exhibited by three different groups of fish. We then report an experimental analysis which confirmed predictions of the model and in turn predicted functional consequences that were explored in behavioral experiments in the pulse fish Gymnotus omarorum. In the experiments, polarization was evaluated by estimating the object's stamp (i.e. the electric source that produces the same electric image as the object) as a function of object impedance, orientation, and position. Signal detection and discrimination was explored in G. omarorum by provoking novelty responses, which are known to reflect the increment in the electric image provoked by a change in nearby impedance. To achieve this, we stepped the longitudinal impedance of a cylindrical object between two impedances (either capacitive or resistive). Object polarization and novelty responses indicate that G. omarorum has two functional regions in the electrosensory field. At the front of the fish, there is a foveal field where object position and orientation are encoded in signal intensity, while the qualia associated with impedance is encoded in signal time course. On the side of the fish there is a peripheral field where the complexity of the polarizing field facilitates detection of objects oriented in any angle with respect to the fish's longitudinal axis. These findings emphasize the importance of articulating field generation, sensor tuning and the repertoire of exploratory movements to optimize performance of artificial active electrosensory systems.