Electric fish measure distance in the dark

Abstract

Distance determination in animals can be achieved by visual or non-visual cues. Weakly electric fish use active electrolocation for orientation in the dark. By perceiving self-produced electric signals with epidermal electroreceptors, fish can detect, locate and analyse nearby objects. Distance discrimination, however, was thought to be hardly possible because it was assumed that confusing ambiguity could arise with objects of unknown sizes and materials. Here we show that during electrolocation electric fish can measure the distance of most objects accurately, independently of size, shape and material. Measurements of the 'electric image' projected onto the skin surface during electrolocation revealed only one parameter combination that was unambiguously related to object distance: the ratio between maximal image slope and maximal image amplitude. However, slope-to-amplitude ratios for spheres were always smaller than those for other objects. As predicted, these objects were erroneously judged by the fish to be further away than all other objects at an identical distance. Our results suggest a novel mechanism for depth perception that can be achieved with a single, stationary two-dimensional array of detectors.

The active electrosensory range ofGymnotus omarorum

“…Theoretical constructs indicate that beyond some critical distance, object images are similar to the image of a sphere (Sicardi et al, 2000). These predictions agree with the experimental data (Rasnow, 1996;Stoddard et al, 1999;Assad et al, 1999;Caputi et al, 2011) and led to an interesting series of behavioral experiments showing that a cube might be confused with a more closely placed sphere (von der Emde et al, 1998). The same reasoning allows one to predict that beyond some distance two objects should not be distinguished from a larger one and that location precision should decay with distance (Pereira and Caputi, 2010).…”

Sensory flow shaped by active sensing: sensorimotor strategies in electric fish

“…This measure was shown to be size invariant and independent from movement direction (Hofmann et al, 2013). Thereby, the tSAR potentially is equally powerful for distance estimation as the pure spatial SAR measure (von der Emde et al, 1998). How well such measures can be used in the analysis of complex electric flow remains to be tested.…”

“…Electric image (EI) is a term used to describe the change of the voltage distribution across the animal's skin due to object-induced modulation in the self-generated electric field. At present we have only a basal understanding of which parameters of these, in many situations ambiguous, sensory images are relevant for behavior (Lewis and Maler, 2002;von der Emde et al, 1998). Most evidently, the location of a simple object can be detected by locating the peak modulation in the EI, while object distance can be estimated from the relative width of the EI.…”

Model based object localization and shape estimation using electric sense on underwater robots

“…Behavioral experiments have shown that these fish can discriminate the size and the shape of objects in the dark. In particular, in [von der Emde et al, 1998], biologists demonstrated that when perceiving an object a fish first identifies its electric nature, then localizes the object and finally recognizes the shape. This behavior is astonishing as it has been shown that using electric sense the separation between localization and object geometric properties is not obvious at all.…”