Estimation of distance and electric impedance of capacitive objects in the weakly electric fish,Gnathonemus petersii

Abstract

During active electrolocation, the weakly electric fish Gnathonemus petersii judges the distance and impedance of nearby objects. Capacitive objects, which modulate local amplitude and waveform of the fish's electric probing signals, cast amplitude and waveform images onto the fish's electroreceptive skin. For an unambiguous estimation of the impedance and distance of an object, the animal has to deal with multiple dependencies of object and image parameters. Based on experimentally recorded amplitude and waveform images, we investigated possible strategies of the fish to unequivocally determine both the distance and the impedance of capacitive objects. We show that the relative slope in amplitude images, but not in waveform images, is independent of object impedance and is a measure of object distance. Distance-invariant impedance estimators were obtained by two different analytical strategies. The peak modulations of both image types were 'calibrated' with the relative slope of the amplitude image. Impedance estimators were obtained whenever these pairs of image features ( peak and relative slope) were related dynamically over two consecutive distances. A static impedance estimator termed 'electric colour' is postulated to arise from the relationship of an amplitude and waveform image. Our results confirm that electric colour is indeed unaffected by object distance. For electric colour estimation we suggest a minimalistic approach of just relating the peak modulations of both image types to the basal amplitude and waveform condition. Our results are discussed with regard to the anatomical and physiological organization of the fish's electrosensory neuronal pathways and behavioural strategies of electrolocating fish.

Electric-Color Sensing in Weakly Electric Fish Suggests Color Perception as a Sensory Concept beyond Vision

“…Although vision and the active electric sense rely on different physical stimuli, color perception in the two modalities results from similar aspects of color formation. Electric colors can be represented as distinct lines (color lines) in a two-dimensional space with amplitude and waveform modulation at its axis (Figure 2) [8,13,14]. This bears close resemblance to the representation of visual color hues, e.g., in the human visual system, which form distinct color lines within their ) and at the side of the head (shown as means ± SD).…”

“…Ambiguities of electrosensory inputs arise when object size, distance, or position vary. While previous reports suggest electrosensory disambiguations when both modulations are combined as electric colors [8,13,14], this concept has never been demonstrated in a natural, behaviorally relevant context. Here, we assessed electric-color perception (1) by recording object-evoked signal modulations and (2) by testing the fishes' behavioral responses to these objects during foraging.…”

“…For each stimulus object, the waveform modulation was plotted versus the amplitude modulation in a two-dimensional space [8,[11][12][13][14] (Figures 2A and 2B). In these graphs, amplitude and waveform modulations recorded at the fovea, e.g., for differently sized animals, and plants could be aligned with five linear functions (Figure 2A, colored lines).…”

Sensory Cues Modulate Smooth Pursuit and Active Sensing Movements

“…The sensory feedback that electric fish perceive as they move through their environment depends on the physical structure of nearby objects (Babineau et al, 2007; Hofmann et al, 2014; Dangelmayer et al, 2016; Gottwald et al, 2017; Schumacher et al, 2017). Because the receptive fields of electrosensory receptors are spatially confined (Krahe and Maler, 2014), the lengths and spatial heterogeneity of the walls of refuges can have dramatic impacts on information encoded by each receptor and by downstream neural populations in the brain (Hofmann and Chacron, 2018).…”

Electrocommunication in pulse Gymnotiformes: the role of EOD time course in species identification.

“…One of these abstractions is the so-called electric color hypothesis proposed (Budelli and Caputi, 2000) upon analysis of previous data (von der Emde, 1990;von der Emde and Ronacher, 1994), and confirmed both in Gnathonemus petersii (Mormyridae; Gottwald et al, 2017Gottwald et al, , 2018 and Gymnotus omarorum (pulse Gymnotiformes; Aguilera and Caputi, 2003;Rodríguez-Cattáneo et al, 2017) in the context of object recognition. Here, we provide evidence that the main parameter used for waveform differentiation in the pair of syntopic species G. omarorum and B. gauderio (when evaluating the EOD of these two species) is encoded in the time course of the signal.…”