Non-visual environmental imaging and object detection through active electrolocation in weakly electric fish

Weakly electric fish orient at night by employing active electrolocation. South American and African species emit electric signals and perceive the consequences of these emissions with epidermal electroreceptors. Objects are detected by analyzing the electric images which they project onto the animal’s electroreceptive skin surface. Electric images depend on size, distance, shape, and material of objects and on the morphology of the electric organ and the fish’s body. It is proposed that the mormyrid Gnathonemus petersii possesses two electroreceptive “foveae” at its Schnauzenorgan and its nasal region, both of which resemble the visual fovea in the retina of many animals in design, function, and behavioral use. Behavioral experiments have shown that G. petersii can determine the resistive and capacitive components of an object’s complex impedance in order to identify prey items during foraging. In addition, fish can measure the distance and three-dimensional shape of objects. In order to determine object properties during active electrolocation, the fish have to determine at least four parameters of the local signal within an object’s electric image: peak amplitude, maximal slope, image width, and waveform distortions. A crucial parameter is the object distance, which is essential for unambiguous evaluation of object properties.     

Distance discrimination during active electrolocation in the weakly electric fish Gnathonemus petersii.

Weakly electric fish use active electrolocation for orientation at night. They emit electric signals (electric organ discharges) which generate an electrical field around their body. By sensing field distortions, fish can detect objects and analyze their properties. It is unclear, however, how accurately they can determine the distance of unknown objects. Four Gnathonemus petersii were trained in two-alternative forced-choice procedures to discriminate between two objects differing in their distances to a gate. The fish learned to pass through the gate behind which the corresponding object was farther away. Distance discrimination thresholds for different types of objects were determined. Locomotor and electromotor activity during distance measurement were monitored. Our results revealed that all individuals quickly learned to measure object distance irrespective of size, shape or electrical conductivity of the object material. However, the distances of hollow, water-filled cubes and spheres were consistently misjudged in comparison with solid or more angular objects, being perceived as farther away than they really were. As training continued, fish learned to compensate for these 'electrosensory illusions' and erroneous choices disappeared with time. Distance discrimination thresholds depended on object size and overall object distance. During distance measurement, the fish produced a fast regular rhythm of EOD discharges. A mechanisms for distance determination during active electrolocation is proposed.     

Three-dimensional analysis of object properties during active electrolocation in mormyrid weakly electric fishes (Gnathonemus petersii)

Weakly electric fishes are nocturnal and orientate in the absence of vision by using their electrical sense. This enables them not only to navigate but also to perceive and recognize objects in complete darkness. They create an electric field around their bodies by producing electric signals with specialized electric organs. Objects within this field alter the electric current at electroreceptor organs, which are distributed over almost the entire body surface. During active electrolocation, fishes detect, localize and analyse objects by monitoring their self-produced electric signals. We investigated the ability of the mormyrid Gnathonemus petersii to perceive objects three-dimensionally in space. Within a range of about 12 cm, G. petersii can perceive the distance of objects. Depth perception is independent of object size, shape and material. The mechanism for distance determination through electrolocation involves calculating the ratio between two parameters (maximal slope and maximal amplitude) of the electrical image which each object projects onto the fish's skin. During active electrolocation, electric fishes cannot only locate objects in space but in addition can determine the three-dimensional shape of an object. Up to certain limits, objects are spontaneously categorized according to their shapes, but not according to their sizes or the materials of which they are made.     

Theoretical analysis of pre-receptor image conditioning in weakly electric fish

Electroreceptive fish detect nearby objects by processing the information contained in the pattern of electric currents through the skin. The distribution of local transepidermal voltage or current density on the sensory surface of the fish's skin is the electric image of the surrounding environment. This article reports a model study of the quantitative effect of the conductance of the internal tissues and the skin on electric image generation in Gnathonemus petersii (Günther 1862). Using realistic modelling, we calculated the electric image of a metal object on a simulated fish having different combinations of internal tissues and skin conductances. An object perturbs an electric field as if it were a distribution of electric sources. The equivalent distribution of electric sources is referred to as an object's imprimence. The high conductivity of the fish body lowers the load resistance of a given object's imprimence, increasing the electric image. It also funnels the current generated by the electric organ in such a way that the field and the imprimence of objects in the vicinity of the rostral electric fovea are enhanced. Regarding skin conductance, our results show that the actual value is in the optimal range for transcutaneous voltage modulation by nearby objects. This result suggests that "voltage" is the answer to the long-standing question as to whether current or voltage is the effective stimulus for electroreceptors. Our analysis shows that the fish body should be conceived as an object that interacts with nearby objects, conditioning the electric image. The concept of imprimence can be extended to other sensory systems, facilitating the identification of features common to different perceptual systems.     

Biomimetic Sensors： Active Electrolocation of Weakly Electric Fish as a Model for Active Sensing in Technical Systems

Instead of vision, many nocturnal animals use alternative senses for navigation and object detection in their dark environment. For this purpose, weakly electric mormyrid fish employ active electrolocation, during which they discharge a specialized electric organ in their tail which discharges electrical pulses. Each discharge builds up an electrical field around the fish, which is sensed by cutaneous electroreceptor organs that are distributed over most of the body surface of the fish. Nearby objects distort this electrical field and cause a local alteration in current flow in those electroreceptors that are closest to the object. By constantly monitoring responses of its electroreceptor organs, a fish can detect, localize, and identify environmental objects.Inspired by the remarkable capabilities of weakly electric fish in detecting and recognizing objects, we designed technical sensor systems that can solve similar problems of remote object sensing. We applied the principles of active electrolocation to technical systems by building devices that produce electrical current pulses in a conducting medium (water or ionized gases) and simultaneously sense local current density. Depending on the specific task a sensor was designed for devices could (i) detect an object, (ii) localize it in space, (iii) determine its distance, and (iv) measure properties such as material properties, thickness, or material faults. Our systems proved to be relatively insensitive to environmental disturbances such as heat, pressure, or turbidity. They have a wide range of applications including material identification, quality control, non-contact distance measurements, medical applications and many more. Despite their astonishing capacities, our sensors still lag far behind what electric fish are able to achieve during active electrolocation. The understanding of the neural principles governing electric fish sensory physiology and the corresponding optimization of our sensors to solve certain technical tasks therefore remain ongoing goals of our research.     

Biomimetic Sensors: Active Electrolocation of Weakly Electric Fish as a Model for Active Sensing in Technical Systems

Instead of vision, many nocturnal animals use alternative senses for navigation and object detection in their dark environment. For this purpose, weakly electric mormyrid fish employ active electrolocation, during which they discharge a specialized electric organ in their tail which discharges electrical pulses. Each discharge builds up an electrical field around the fish, which is sensed by cutaneous electroreceptor organs that are distributed over most of the body surface of the fish. Nearby objects distort this electrical field and cause a local alteration in current flow in those electroreceptors that are closest to the object. By constantly monitoring responses of its electroreceptor organs, a fish can detect, localize, and identify environmental objects.Inspired by the remarkable capabilities of weakly electric fish in detecting and recognizing objects, we designed technical sensor systems that can solve similar problems of remote object sensing. We applied the principles of active electrolocation to technical systems by building devices that produce electrical current pulses in a conducting medium (water or ionized gases) and simultaneously sense local current density. Depending on the specific task a sensor was designed for devices could (i) detect an object, (ii) localize it in space, (iii) determine its distance, and (iv) measure properties such as material properties, thickness, or material faults. Our systems proved to be relatively insensitive to environmental disturbances such as heat, pressure, or turbidity. They have a wide range of applications including material identification, quality control, non-contact distance measurements, medical applications and many more. Despite their astonishing capacities, our sensors still lag far behind what electric fish are able to achieve during active electrolocation. The understanding of the neural principles governing electric fish sensory physiology and the corresponding optimization of our sensors to solve certain technical tasks therefore remain ongoing goals of our research.     

Capacitance detection in the wave-type electric fish Eigenmannia during active electrolocation

Weakly electric fish can detect nearby objects and analyse their electric properties during active electrolocation. Four individuals of the South American gymnotiform fish Eigenmannia sp., which emits a continuous wave-type electric signal, were tested for their ability to detect capacitive properties of objects and discriminate them from resistive properties. For individual fish, capacitive values of objects had to be greater than 0.22–1.7 nF (`lower threshold') and smaller than 120–680 nF (`upper threshold') in order to be detected. The capacitive values of natural objects fall well within this detection range. All fish trained could discriminate unequivocally between capacitive and resistive object properties. Thus, fish perceive capacitive properties as a separate object quality. The effects of different types of objects on the locally occurring electric signals which stimulate electroreceptors during electrolocation were examined. Purely resistive objects altered mainly local electric organ discharge (EOD) amplitude, but capacitive objects with values between about 0.5 and 600 nF changed the timing of certain EOD parameters (phase-shift) and EOD waveform. A mechanism for capacitance detection in wave-type electric fish based on time measurements is proposed and compared with the capacitance detection mechanism in mormyrid pulse-type fish, which is based on waveform measurements. Accepted: 31 July 1997     

Active electric imaging: body-object interplay and object's "electric texture"

This article deals with the role of fish's body and object's geometry on determining the image spatial shape in pulse Gymnotiforms. This problem was explored by measuring local electric fields along a line on the skin in the presence and absence of objects. We depicted object's electric images at different regions of the electrosensory mosaic, paying particular attention to the perioral region where a fovea has been described. When sensory surface curvature increases relative to the object's curvature, the image details depending on object's shape are blurred and finally disappear. The remaining effect of the object on the stimulus profile depends on the strength of its global polarization. This depends on the length of the object's axis aligned with the field, in turn depending on fish body geometry. Thus, fish's body and self-generated electric field geometries are embodied in this "global effect" of the object. The presence of edges or local changes in impedance at the nearest surface of closely located objects adds peaks to the image profiles ("local effect" or "object's electric texture"). It is concluded that two cues for object recognition may be used by active electroreceptive animals: global effects (informing on object's dimension along the field lines, conductance, and position) and local effects (informing on object's surface). Since the field has fish's centered coordinates, and electrosensory fovea is used for exploration of surfaces, fish fine movements are essential to perform electric perception. We conclude that fish may explore adjacent objects combining active movements and electrogenesis to represent them using electrosensory information.     

Distance discrimination during active electrolocation in the weakly electric fish Gnathonemus petersii

Weakly electric fish use active electrolocation for orientation at night. They emit electric signals (electric organ discharges) which generate an electrical field around their body. By sensing field distortions, fish can detect objects and analyze their properties. It is unclear, however, how accurately they can determine the distance of unknown objects. Four Gnathonemus petersii were trained in two-alternative forced-choice procedures to discriminate between two objects differing in their distances to a gate. The fish learned to pass through the gate behind which the corresponding object was farther away. Distance discrimination thresholds for different types of objects were determined. Locomotor and electromotor activity during distance measurement were monitored. Our results revealed that all individuals quickly learned to measure object distance irrespective of size, shape or electrical conductivity of the object material. However, the distances of hollow, water-filled cubes and spheres were consistently misjudged in comparison with solid or more angular objects, being perceived as farther away than they really were. As training continued, fish learned to compensate for these 'electrosensory illusions' and erroneous choices disappeared with time. Distance discrimination thresholds depended on object size and overall object distance. During distance measurement, the fish produced a fast regular rhythm of EOD discharges. A mechanisms for distance determination during active electrolocation is proposed.     

Distance and shape: perception of the 3-dimensional world by weakly electric fish.

Weakly electric fish orient at night in complete darkness by employing their active electrolocation system. They emit short electric signals and perceive the consequences of these emissions with epidermal electroreceptors. Objects are detected by analyzing the electric images which they project onto the animal's electroreceptive skin surface. This process corresponds to similar processes during vision, where visual images are cast onto the retinas of eyes. Behavioral experiments have shown that electric fish can measure the distance of objects during active electrolocation, thus possessing three-dimensional depth perception of their surroundings. The fundamental mechanism for distance determination differs from stereopsis used during vision by two-eyed animals, but resembles some supplementary mechanisms for distance deduction in humans. Weakly electric fish can also perceive the three-dimensional shape of objects. The fish can learn to identify certain objects and discriminate them from all other objects. In addition, they spontaneously categorize objects according to their shapes and not according to object size or material properties. There is good evidence that some fundamental types of perceptional invariances during visual object recognition in humans are also found in electric fish during active electrolocation. These include size invariance (maybe including size constancy), rotational invariance, and translational invariance. The mechanisms of shape detection during electrolocation are still unknown, and their discoveries require additional experiments.     

Spatial aspects of electrolocation in the mormyrid fish, Gnathonemus petersii

The range of electrolocation in the weakly electric fish, Gnathonemus petersii, was determined for plastic and aluminium cubes. A characteristic change in the fish's EOD activity, and abrupt change to more uniform EOD intervals (regularization), was used as the criterion for object detection. The average response distances extending laterally from the fish's longitudinal axis were significantly different (p less than 0.05) for the aluminium cube (5.4 cm) and the plastic cube (7.0 cm).     

Behavioral evidence of a latency code for stimulus intensity in mormyrid electric fish

Mormryid electric fish (Gnathonemus petersii) respond to novel stimuli with an increase in the rate of the electric organ discharge (EOD). These novelty responses were used to measure the fish's ability to detect small changes in the amplitude and latency of an electrosensory stimulus. Responses were evoked in curarized fish in which the EOD was blocked but in which the EOD motor command continued to be emitted. An artificial EOD was provided to the fish at latencies of 2.4 to 14.4 ms following the EOD motor command.Novelty responses were evoked in response to transient changes in artificial EOD amplitude as small as 1% of baseline amplitude, and in latency as small as 0.1 ms. Changes in latency were effective only at baseline delays of less than 12.4 ms.The sensitivity to small changes in latency supports the hypothesis that latency is used as a code for stimulus intensity in the active electrolocation system of mormyrid fish. The results also indicate that a corollary discharge signal associated with the EOD motor command is used to measure latency.Abbreviations EOD electric organ discharge - ELL electrosensory lateral line lobe - epsp excitatory post synaptic potential     

Electrolocation of Capacitive Objects in Four Species of Pulse-type Weakly Electric Fish I. Discrimination Performance

The great variety of species-typical electric signals (electric organ discharges, EOD) emitted by weakly electric mormyrid fish might be the result of evolutionary pressures stemming from the two main functions of the electro-sensory-motor system: electrocommunication and electrolocation. Employing a conditioned discrimination task we tested four species of mormyrids, emitting EODs differing in waveform, for their ability to detect capacitive properties of objects during electrolocation. Each fish could discriminate capacitive objects within a certain range of capacitive values, which was species specific. The upper and lower limits (upper and lower thresholds) of this detectable range were determined for each fish. In fish species emitting long duration EODs composed of mainly low spectral frequencies both the lower and the upper thresholds were shifted to larger capacitive values compared to fish species emitting shorter EODs. The upper limit of the detectable range was much more variable between species than the lower limit, which was relatively low in all fish. We interpret this as an adaptation of mormyrids to detect small capacitive objects, for example food items. All mormyrids could discriminate between a resistive object and a capacitive object even if the complex impedances of the two objects were identical. This implies that the fish are highly sensitive to small waveform distortions of their self produced EODs.     

Communication in the weakly electric fish Sternopygus macrurus

There is a sexual dimorphism in the frequency of the quasi-sinusoidal electric organ discharge (EOD) of Sternopygus macrurus, with males, on average, an octave lower. EODs are detected by tuberous electroreceptor organs, which exhibit V-shaped frequency tuning with maximal sensitivity near the fish's own EOD frequency. This would seem to limit the ability of a fish to detect the EODs of opposite-sex conspecifics. However, electroreceptor tuning has always been based on single-frequency stimulation, while actual EOD detection involves the addition of a conspecific EOD to the fish's own. In the present study, recordings were made from single electroreceptive units while the fish were stimulated with pairs of sine waves: one (S1) representing the fish's own EOD added to a second (S2) representing a conspecific EOD. T unit response was easily predicted by assuming that the electroreceptor acts as a linear filter in series with a threshold-sensitive spike initiator. P unit response was more complex, and unexpectedly high sensitivity was found for frequencies of S2 well displaced from the fish's EOD frequency. For both P and T units, detection thresholds for S2 were much lower when added to S1, than when presented alone.     

Modeling the electric image produced by objects with complex impedance in weakly electric fish

Weakly electric fish generate an electric field around their body by electric organ discharge (EOD). By measuring the modulation of the electric field produced by an object in the field these fish are able to accurately locate an object. Theoretical and experimental studies have focused on the amplitude modulations of EODs produced by resistive objects. However, little is known about the phase modulations produced by objects with complex impedance. The fish must be able to detect changes in object impedance to discriminate between food and nonfood objects. To investigate the features of electric images produced by objects with complex impedance, we developed a model that can be used to map the electric field around the fish body. The present model allows us to calculate the spatial distribution of the amplitude and phase shift in an electric image. This is the first study to investigate the changes in amplitude and phase shift of electric images induced by objects with complex impedance in wave-type fish. Using the model, we show that the amplitude of the electric image exhibits a sigmoidal change as the capacitance and resistance of an object are increased. Similarly, the phase shift exhibits a significant change within the object capacitance range of 0.1–100 nF. We also show that the spatial distribution of the amplitude and phase shifts of the electric image resembles a “Mexican hat” in shape for varying object distances and sizes. The spatial distribution of the phase shift and the amplitude was dependent on the object distance and size. Changes in the skin capacitance were associated with a tradeoff relationship between the magnitude of the amplitude and phase shift of the electric image. The specific range of skin capacitance (1–100 nF) allows the receptor afferents to extract object features that are relevant to electrolocation. These results provide a useful basis for the study of the neural mechanisms by which weakly electric fish recognize object features such as distance, size, and impedance.     

Behavioral detection of electric signal waveform distortion in the weakly electric fish,Gnathonemus petersii

The novelty response of weakly electric mormyrids is a transient acceleration of the rate of electric organ discharges (EOD) elicited by a change in stimulus input. In this study, we used it as a tool to test whether Gnathonemus petersii can perceive minute waveform distortions of its EOD that are caused by capacitive objects, as would occur during electrolocation. Four predictions of a hypothesis concerning the mechanism of capacitance detection were tested and confirmed: (1) G. petersii exhibited a strong novelty response to computer-generated (synthetic) electric stimuli that mimic both the waveform and frequency shifts of the EOD caused by natural capacitive objects (Fig. 3). (2) Similar responses were elicited by synthetic stimuli in which only the waveform distortion due to phase shifting the EOD frequency components was present (Fig. 4). (3) Novelty responses could reliably be evoked by a constant amplitude phase shifted EOD that effects the entire body of the fish evenly, i.e., a phase difference across the body surface was lacking (Figs. 3, 4). (4) Local presentation of a phase-shifted EOD mimic that stimulated only a small number of electroreceptor organs at a single location was also effective in eliciting a behavioral response (Fig. 5).Our results indicate that waveform distortions due to phase shifts alone, i.e. independent of amplitude or frequency cues, are sufficient for the detection of capacitive, animate objects. Mormyrids perceive even minute waveform changes of their own EODs by centrally comparing the input of the two types of receptor cells within a single mormyromast electroreceptor organ. Thus, no comparison of differentially affected body regions is necessary. This shows that G. petersii indeed uses a unique mechanism for signal analysis, which is different from the one employed by gymnotiform wavefish.Abbreviations EOD electric organ discharge - p-p-amplitude peak-to-peak amplitude     

Electroreceptor model of the weakly electric fish Gnathonemus petersii. I. The model and the origin of differences between A- and B-receptors.

We present an electroreceptor model of the A- and B-receptors of the weakly electric fish Gnathonemus petersii. The model consists of a sensory cell, whose membrane is separated into an apical and basal portions by support cells, and an afferent fiber. The apical membrane of the cell contains only leak channels, while the basal membrane contains voltage-sensitive Ca2+ channels, voltage-sensitive and Ca2+-activated K+ channels, and leak channels. The afferent fiber is described with the modified Hodgkin-Huxley equation, in which the voltage-sensitive gate of the K+ channels is a dynamic variable. In our model we suggest that the electroreceptors detect and process the information provided by an electric organ discharge (EOD) as follows: the current caused by an EOD stimulus depolarizes the basal membrane to a greatly depolarized state. Then the release of transmitter excites the afferent fiber to oscillate after a certain time interval. Due to the resistance-capacitance structure of the cells, they not only perceive the EOD intensity, but also sense the variation of the EOD waveform, which can be strongly distorted by the capacitive component of an object. Because of the different morphologies of A- and B-cells, as well as the different conductance of leak ion channels in the apical membrane and the different capacitance of A- and B-cells, A-receptors mainly respond to the EOD intensity, while B-receptors are sensitive to the variation of EOD waveform.     

Swimming Patterns Associated with Foraging in Phylogenetically and Ecologically Diverse American Weakly Electric Teleosts (Gymnotiformes)

The backwards swimming behavior exhibited by American weakly electric fishes (Gymnotiformes) is thought to be an important component of foraging, particularly in the electrolocation of prey items. Previous studies of Eigenmannia virescens and Apteronotus albifrons have shown that backwards swimming appears to allow a fish to scan a potential prey item across its cutaneous electroreceptor array, then put itself in position for a short, forward lunge preceding ingestion. Adult gymnotiforms exhibit considerable variation in size, shape, and electric organ characteristics. For example, gymnotiforms produce either a wave or a pulse electric organ discharge (EOD). Given this variation, we ask whether the results reported previously can be completely generalized to all gymnotiforms. To address this question we observed the foraging patterns of phylogenetically and ecologically distinct gymnotiforms: three wave species, E. virescens, A. albifrons and Sternopygus macrurus; and three pulse species, Gymnotus carapo, Brachyhypopomus cf. brevirostris, and Rhamphichthys rostratus. Electric organ placement and body shape were also noted in these species to determine if morphological differences correlate with variations in foraging behaviors. Results demonstrate that following prey detection the wave species examined primarily swim backwards during prey approach, prior to lunging forward and ingesting prey. This result is similar to previous findings. In contrast, the pulse species examined detect, approach, and ingest prey primarily in the forward direction, swimming backwards only to reposition themselves.     

Electrolocation in the presence of jamming signals: electroreceptor physiology

Responses of ampullary and tuberous electroreceptor afferents were studied using moving electrolocation targets and electrical modulations of the animal's electric organ discharge as stimuli. The ability of the electroreceptors to encode these stimuli was measured with and without various forms of electrical jamming signals. The goal of this study was to measure the deterioration in electroreceptor responses due to the jamming signals, and to compare these results with the behavioral measures of electrolocation under the same conditions of jamming as described in the preceding report (Bastian 1987). 1. Three types of jamming stimuli were used to interfere with the tuberous electroreceptor afferents' ability to respond to the test stimuli mentioned above: Broad-band noise, high frequency stimuli consisting of a sinusoidal waveform having a frequency maintained at a chosen difference frequency (DF) from the EOD frequency of the fish being studied, and 5 or 50 Hz sinusoidal stimuli. 2. The tuberous receptor afferents' spontaneous frequency was sensitive to continuous presentation of all but the 5 Hz jamming signals. The 4 Hz DF signal caused the largest increase in spontaneous activity, the 50 Hz stimulus was intermediate in effectiveness, and the noise stimulus caused the smallest increase. Estimates of the variability of the ongoing receptor activity were also made, and both the 4 Hz DF and the 50 Hz stimuli reduced the coefficient of variation of the receptor activity, but noise had no significant effect on this parameter. Noise, 4 Hz DF, and 50 Hz jamming signals also reduced the tuberous receptors' responses to a 100 ms EOD amplitude modulation, and the 5 Hz stimulus was again ineffective. 3. Noise and 4 Hz DF jamming were also effective in reducing tuberous receptor afferents' responses to a moving metal electrolocation target. The 4 Hz DF stimulus was most effective in reducing the receptor's ability to encode information about the target. Receptor responses showed about a three-fold larger decrease per 10 dB increase in DF jamming amplitude as compared to similar sized increases in noise amplitude. Threshold target distances were also determined with and without noise and DF jamming, and again, the noise stimulus was less effective in reducing the distance at which electrolocation targets were just detectable. 4. Recordings from ampullary receptor afferents confirmed that the galvanic potentials produced by metal electrolocation targets stimulate these receptors while EOD distortions caused by such objects probably do not.(ABSTRACT TRUNCATED AT 400 WORDS)     

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.