[RESUMEN] ABSTRACT

The distance to an object may be estimated using several sensory systems. The most familiar for us is vision. Two unrelated orders of fish, one from Africa and the other from America, are unable to use visual cues since they are nocturnal and often live in muddy waters. They might use, instead, a unique sensory system discovered only recently, in 1958. It consists of an organ that produces electric currents, a set of electroreceptors distributed throughout the skin and some highly specialized structures of the nervous system. Objects in the vicinity of the fish modify its electric field as a function of their resistive and capacitive properties. This modification is detected by the skin receptors and used to infer the shape and position of these objects. It is known that these fish, using this system, are able to detect objects in the environment and discriminate some of their characteristics. Nevertheless, it was unclear whether they were able to estimate distances. In this paper we report results from behavioral and electrophysiological studies and computational models demonstrating that this system is able to discriminate distances. In addition, we describe the cues used by the fish to achieve this task.