Fish perform spatial pattern recognition and abstraction by exclusive use of active electrolocation

The field generated by the electric organ of weakly electric fish varies with the electrical properties of nearby objects. Correspondingly, current fluxes in this field differentially stimulate the electroreceptors in the fish's skin. Thus, resistors are to conductors and insulators as gray is to black and white in optics. Additionally, the capacitances of plants and insect larvae contrast with those of water or stones, giving effects comparable to "coloration". Receptors arrayed over a large area of the skin act like a retina upon which the discharge projects "electric images". By further central processing, the fish also discriminate between objects according to their composition, size, or distance, a procedure termed "electrolocation", analogous to echolocation in bats. Here we demonstrate that G. petersii and S. macrurus can also recognize 3D orientations and configurations and extract and generalize spatial features solely with their electrical sense. We presented fish with virtual electrical "objects" formed from electrodes set flush in the inner surface of a Y maze with various patterns of external connectivity. With reward and aversion training, the fish could recognize similar electrode configurations and extract a feature, e.g., a vertical connectivity, present in various novel configurations. Previously, shape recognition has only been shown in electrolocating fish when they are in full mechanical contact with solid objects.