Modeling signal and background components of electrosensory scenes

“Empirical measurements indicate that the return signal for the active electric sense falls off approximately as the fourth power of distance for small targets over the behaviorally relevant range of target distances (Chen et al. 2005), similar to geometric spreading effects in other systems.”

“This may facilitate sensory performance as the body houses the electric field generator, and movement of the tail causes modulations of the field that are more than a factor of 10 larger than prey-related modulations (Chen et al., 2005; Nelson and MacIver, 1999).”

“(A) Magnitude of the self-generated electric field in water of 35-lS/cm conductivity from an empirically validated computational model [41].”

“tail bends) [7], as well as spatially diffuse images caused by conspecifics [8].”

“Although a number of studies have investigated the spatial formation of EIs and the influence of objects within a static electric scene (for a review, see Caputi and Budelli, 2006), information about spatiotemporal EI dynamics is sparse (Babineau et al., 2007; Chen et al., 2005; Hofmann et al., 2013; Sim and Kim, 2011…”

“DOI:10.1523/JNEUROSCI.0998-13.2013 Copyright © 2013 the authors 0270-6474/13/3313758-15$15.00/0 (Rasnow et al., 1993; Bastian, 1995; Assad et al., 1999; Chen et al., 2005; Yu et al., 2012).”

“…that is greater (such as other organisms and aquatic foliage) or less (such as rocks and wood) than that of the ambient water cause spatially localized increases or decreases, respectively, in the amplitude of the electric field relative to the background intensity caused by the ongoing EOD 4,5 .”

“Many recent studies have contributed to our understanding of electrosensory scene analysis [9,26,27,33,34].”

“Also, the model currently only simulates the EOD potential for a single phase of the EOD cycle [as in other recent models (see, for example, Chen et al., 2005)].”

“THE JOURNAL OF EXPERIMENTAL BIOLOGY 1573Movement shapes sensory feedback modulations of the strength of the electric field on the ipsilateral and contralateral sides with opposite signs (Chen et al., 2005).”

“The equations of Chen et al. (2005) are then used to estimate the shape of the electric image induced by this sphere on the fish’s skin.”

“tail movements [35,36].”

“Active electro-sensing has driven an increasing number of experimental, behavioral, biological, and computational studies since Lissmann and Machin’s work [11, 12, 15, 17, 23, 24, 30, 36].”

“Apteronotus will scan for prey at velocities (Ͼ10 cm/s) producing stimulus bandwidths ϳ20 –30 Hz; stimulus intensities at the moment of detection are often weak, Ͻ1 ␮V for prey Ͼ2 cm away (Babineau et al. 2006; Bastian 1981a; Chen et al. 2005; Nelson and MacIver 1999).”

“These simple objects, such as spheres or cubes, are known to produce a mexican-hat-shaped electric image, whose peak location, amplitude and width vary systematically with object location relative to the fish for a fixed phase of the EOD cycle (von der Emde 1999; Chen et al. 2005; Babineau et al. 2006; Caputi and Bude…”

“Changes in the position of electroreceptors relative to the electric organ resulting from movements of the tail cause changes in EOD amplitude that may be substantially larger than those caused by many behaviorally relevant external stimuli (Bastian, 1995; Chen et al., 2005).”

“The spatial and temporal features of the electric field are complex (Chen et al., 2005) and vary as a function of objects in the environment and the presence of other electric fish (Kelly et al.”

“Perturbations in the EOD due to swimming movements of the fish and large objects might be 10 or even 100 times larger than changes induced by prey [36,37].”

“Ramcharitar JU, Tan EW, Fortune ES: Global electrosensory oscillations enhance directional responses of midbrain neurons in Eigenmannia.”

“Finally, because the field generator is in the trunk, movement of the body causes large distortions of the emitted signal, possibly favoring holding the trunk rigid [37,38] rather than using it for propulsion.”

“Large objects in the environment will produce large, blurred images that will not change when the animal is moving, whereas the electric images of smaller objects (prey) nearby will change to a stronger degree (Babineau et al. 2007; Chen et al. 2005), leaving an “electrical signature” (electric flow) that animals coul…”

“1 Analytical model of measurement The sensor is modeled as an array of m+1 spherical conducting electrodes aligned on a rigid line that forms a solid axis [CHKN05].”

“Changes in afferent activity caused by movements may be 10 or even 100 times larger than those induced by prey (Chen et al., 2005).”

“The scale of an " upstroke " in a dynamic electrosensory scene might represent how close the fish is to prey during its hunting scans of the environment (Chen et al. 2005; Nelson and MacIver 1999; D. Babineau, A. Longtin, and J. E. Lewis, unpublished data).”

“, 1998) and the half-maximum width of electric images (Lewis and Maler, 2001; Chen et al., 2005), the temporal SAR (Sim and Kim, 2012; Hofmann et al.”

“Key words: fluid-structure interaction, immersed boundary method, electrolocation, dielectrophoresis, self-assembly, distributed Lagrange multipliers, adaptive mesh refinement, free swimming, knifefish, nanowires”

“In the active electrosensory systems of mormyrid and gymnotid fish swimming movements alter the position of the electric organ (located in the tail) relative to the sensory surface and have strong effects on activity in electroreceptors (Bastian, 1995; Chen et al., 2005; Sawtell and Williams, 2008).”

“Far-field characteristics of EODs The electric near-field of electric fish is asymmetrically distorted along the body axis because of the elongated electric organ (Heiligenberg, 1973; Rasnow and Bower, 1996; Assad et al., 1998, 1999; Stoddard et al., 1999; Chen et al., 2005).”

“1B shows data obtained from the recording dipole with an overlay of the expected change in electric potential according to an empirically derived relationship (9).”

“The modeled physical signal (green) is symmetric with respect to distance (Chen et al., 2005), which we confirmed experimentally (gray).”

“Previous studies have shown that the location of the peak of self-images on the skin is a reliable cue for object location, and the spatial profile (for example, width) of self-images provides information about object size, shape and distance 23–25 .”

“…transforms EA firing rates to accurately encode Model traces of the electric potential experienced on the skin of the fish for the final 2cm of looming (or first 2cm of receding), caused by brass (yellow) and plastic (grey) spheres with small ( d ¼ 0.64cm) and large ( d ¼ 1.21cm) diameters 9 .”

“One particular type of motion-related cues is found during the analysis of tail bending motions (Chen et al., 2005; Sim and Kim, 2010).”

“Other groups have validated the model by comparison with analytical methods (Assad et al., 1999; Chen et al., 2005).”

“” Active electrosense has been extensively studied in biology[4], [20] as a model system for understanding how sensory signals are processed by the nervous system.”

“Apteronotus (Chen et al., 2005) and also in artificial electrosensoy artifacts (MacIver et al.”

“However, in closerange situations the dipole approximation does not hold and has to be modelled as a multipole system with one caudal pole and multiple rostral poles [11].”

“LEOD amplitude modulations in a swimming fish would also be characterized by correlations on multiple timescales, resulting from movement of the fish, boundary conditions, and foreground objects (Chen et al., 2005).”

“[7] describe the effects of spherical objects located in an electric field as”

“…the electrosensory system of wave-type gymnotiform fish because of their behavioral sensitivity to very weak electric signals emanating from prey (Chen et al. 2005; Nelson and MacIver 1999) and the extensive knowledge of their low-level electrosensory circuitry (Maler 2009a), but we expect that…”

“To improve the accuracy near the wall, the dipole model of the WEF could include the effects of the physically distributed current sources [11,67].”

“The electric organ discharge is used for orientation and object detection in close vicinity of the fish [12,13], and for communication with conspecifics [7,14-19].”

“One suggested reason is that the trunk carries the electrical emission system of the fish; thus, when the tail bends, there is a large modulation of the sensory receptors on the trunk surface (Bastian 1995; Chen et al. 2005).”

“For the exponent of the power law, a value of α ≈ 4 has been observed in Apteronotus albifrons ( Chen, House, Krahe, & Nelson, 2005 ).”

“Movements alter the position of the electric organ relative to electroreceptors and result in changes in the electric field that are as large, or larger, than those attributable to behaviorally relevant stimuli (Bastian, 1995; Chen et al., 2005; Sawtell and Williams, 2008; Fotowat et al., 2013).”

“Edu position and orientation dependent [4].”

“…and temporal characteristics depend on the distribution of impedance (Bacher, 1983; Budelli and Caputi, 2000; Caputi and Budelli, 1995; Caputi et al.,1998; Chen et al., 2005; Heiligenberg, 1973; Lissmann and Machin, 1958; Rasnow, 1996; SanguinettiScheck et al., 2011; Scheich and Bullock, 1974).”

“…pulse amplitude depends approximately on the distance from the recording electrodes and the orientation of the fish according to the formula (Chen et al. 2005): ⌽ ͑ r, ␪ ͒ ϭ Idcos␪ 4␲␴r 2 (1) where I is the current generated by the dipole, d is the length of the dipole, ␪ is the angle…”

“Past work on electrosense has dealt extensively with object recognition and detection at different salinities [1], [4], [12], but few have tried to tackle the Simultaneous Localizing and Mapping (SLAM) problem using this sensor modality.”

“2.2 Electric image calculation In previous studies, the electric image was calculated using the changes in amplitude modulation of the transdermal voltage (represented as a real number) (Hoshimiya et al. 1980; Chen et al. 2005; Migliaro et al. 2005; Babineau et al. 2006).”

“5 Hz, 5 Hz, 10 Hz, 15 Hz, 20 Hz, and 30 Hz in increasing order assuming a Gaussian electric image of 1 cm standard deviation (Bastian et al. 2002; Chen et al. 2005).”

“How the shape and amplitude of electric images look in detail has been studied both experimentally and theoretically (Heiligenberg, 1975; Bastian, 1981; Bacher, 1983; Rasnow, 1986; Chen et al., 2005; Babineau et al., 2006).”

“The characteristics of the field created by this discharge (EOD) depend on the degree of polarization of the elements of the scene – which in turn depend on objects’ impedance in relation to the conductivity of the water and the fish – as well as on the relative position of the elements, and the field geometry (Lissma…”

“The electric organ acts as a current source 26 , and has been described in different ways in previous models 11,18,20 .”

“For simulation, we set the body length equal to 21 cm and fix the electric pole density to 10 poles per cm, following the biological body models (Babineau et al., 2006; Chen et al., 2005).”

“At large distances of more than a body length, the peak intensity falls approximately as d-4, where d is the distance from the midline of the body (Chen et al. 2005).”

“These electric poles are arranged along the mid-line of the fish at uniform intervals of 0.1 cm (Chen et al., 2005; Sim & Kim, 2011b).”

“Specifically, tail bending induces changes in the relative geometry between the electrosensory organ and the electroreceptor, which generally causes an amplitude modulation: a stronger electric field on the ipsilateral side of bending while a weaker stimulation on the contralateral side [52, 53].”

“Note also that this result applies to electric fish as their unperturbed electric field is well described by a line of point charges [15].”

“In fact, active electro-sensing has motivated an increasing number of experimental, behavioral, biological, and computational studies since Lissmann and Machins work [12, 13, 16, 18, 23, 24, 27, 28].”

“A lot of effort has also been devoted to the electro-sensing problem, that is, the capability of the animal to detect and recognize a dielectric target nearby [26, 31, 8, 9, 12, 16, 27, 28, 32, 35, 36, 37].”

“The electrode tips were exposed differentially (1mm at the tail & 1 cm at the head) and were separated by 2.5 cm to reproduce the asymmetrical electric field geometry that occurs along the rostral to caudal axis in real fish (Assad et al., 1999; Chen et al., 2005; Babineau et al., 2006; Hupé, 2012).”

“As the self-generated electric field attenuates with a power function of distance [16,21,24,25], these object-emitted signals also decay with a power function of distance.”