@article {542, title = {Object discrimination through active electrolocation: Shape recognition and the influence of electrical noise}, journal = {Journal of Physiology-Paris}, year = {2016}, month = {Jan-12-2016}, abstract = {

The weakly electric fish Gnathonemus petersii can recognise objects using active electrolocation. Here, we tested two aspects of object recognition; first whether shape recognition might be influenced by movement of the fish, and second whether object discrimination is affected by the presence of electrical noise from conspecifics. (i) Unlike other object features, such as size or volume, no parameter within a single electrical image has been found that encodes object shape. We investigated whether shape recognition might be facilitated by movement-induced modulations (MIM) of the set of electrical images that are created as a fish swims past an object. Fish were trained to discriminate between pairs of objects that either created similar or dissimilar levels of MIM of the electrical images. As predicted, the fish were able to discriminate between objects up to a longer distance if there was a large difference in MIM between the objects than if there was a small difference. This supports an involvement of MIMs in shape recognition but the use of other cues cannot be excluded. (ii) Electrical noise might impair object recognition if the noise signals overlap with the EODs of an electrolocating fish. To avoid jamming, we predicted that fish might employ pulsing strategies to prevent overlaps. To investigate the influence of electrical noise on discrimination performance, two fish were tested either in the presence of a conspecific or of playback signals and the electric signals were recorded during the experiments. The fish were surprisingly immune to jamming by conspecifics: While the discrimination performance of one fish dropped to chance level when more than 22\% of its EODs overlapped with the noise signals, the performance of the other fish was not impaired even when all its EODs overlapped. Neither of the fish changed their pulsing behaviour, suggesting that they did not use any kind of jamming avoidance strategy.

}, issn = {09284257}, doi = {10.1016/j.jphysparis.2016.11.008}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0928425716300304}, author = {Schumacher, Sarah and Burt de Perera, Theresa and G. von der Emde} } @inbook {486, title = {Matched Filtering in African Weakly Electric Fish: Two Senses with Complementary Filters}, booktitle = {The Ecology of Animal Senses}, year = {2016}, pages = {237 - 263}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, address = {Cham}, abstract = {

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.

}, isbn = {978-3-319-25490-6}, doi = {10.1007/978-3-319-25492-010.1007/978-3-319-25492-0_9}, url = {http://link.springer.com/10.1007/978-3-319-25492-0}, author = {G. von der Emde and Ruhl, Tim}, editor = {G. von der Emde and Warrant, Eric} } @article {412, title = {The electric organ discharges of the Petrocephalus species (Teleostei: Mormyridae) of the Upper Volta System}, journal = {Journal of Fish Biology}, volume = {74}, number = {1}, year = {2009}, note = {395IDTimes Cited:0Cited References Count:40}, month = {Jan}, pages = {54-76}, abstract = {

In this study, a first comparative investigation of all four species of Petrocephalus (P. bovei, P. bane, P. soudanensis and P. cf. pallidomaculatus) present in the Upper Volta system and their electric organ discharges (EOD) was conducted. It was found that P. bovei was the most widespread (in terms of habitat use), but in several places P. bovei, P. soudanensis and P. cf. pallidomaculatus occurred syntopically. All species emitted a triphasic signal, and with very few exceptions, the Petrocephalus species of the Upper Volta system could clearly be identified on the basis of their EOD waveforms. The most obvious differences between species in EOD waveforms were in amplitude of the last phase, total duration and fast Fourier transformation (FFT) peak frequency. No sexual dimorphism was present in the EOD of any species although external dimorphism, i.e. an indentation at the base of the anal fin of mature males, was common. The EOD waveform diversity in the Upper Volta principally resembled that found in four sympatric Petrocephalus species from the OgoouE system (Gabon) and might play a role in species recognition and speciation processes.

}, keywords = {active electrolocation, central-africa, communication, eod waveform, fishes mormyridae, gnathonemus-petersii mormyridae, osteoglossomorpha, pendjari, pollimyrus-isidori, recognition, sex-differences, speciation, variability, water conductivity, weakly electric fish, west africa}, isbn = {0022-1112}, url = {://000262516900004}, author = {Moritz, T. and Engelmann, J. and Linsenmair, K. E. and G. von der Emde} }