Matched Filtering in African Weakly Electric Fish: Two Senses with Complementary Filters

African weakly electric fish live nocturnally in tropical freshwater streams. To sense their surroundings, they have developed a highly specialized system of two senses, which allows them to perceive nearby objects at high precision with an active electric sense and to detect large, fast-moving objects with their visual sense at greater distances. Both senses are highly specialized and are equipped with matched filters for efficient detection and analysis of relevant object features and for neglecting unimportant items. Active electrolocation in the near field involves the production of an electric signal, which serves as a carrier for sensory information. This signal and the resulting electric field around the fish are shaped by the fish’s body and its internal structure. The electric skin properties and the accessory structures of the electroreceptor organs further filter the signal and form two electroreceptive foveae. In contrast, the visual system is adapted for detecting large objects at longer distances. A grouped retina forms a visual matched filter, which filters out small, nearby objects but efficiently detects fast-moving distant objects even under noisy and dim light conditions.