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Spatial acuity and prey detection in weakly electric fish.

Babineau D, Lewis JE, Longtin A - PLoS Comput. Biol. (2007)

Bottom Line: This shows explicitly how the back-and-forth swimming, characteristic of these fish, can be used to generate motion cues that, as in other animals, assist in the extraction of sensory information when signal-to-noise ratios are low.Our study also reveals the importance of the structure of complex electrosensory backgrounds.Whereas large-object spacing is favorable for discriminating the individual elements of a scene, small spacing can increase the fish's ability to resolve a single target object against this background.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, University of Ottawa, Ottawa, Ontario, Canada.

ABSTRACT
It is well-known that weakly electric fish can exhibit extreme temporal acuity at the behavioral level, discriminating time intervals in the submicrosecond range. However, relatively little is known about the spatial acuity of the electrosense. Here we use a recently developed model of the electric field generated by Apteronotus leptorhynchus to study spatial acuity and small signal extraction. We show that the quality of sensory information available on the lateral body surface is highest for objects close to the fish's midbody, suggesting that spatial acuity should be highest at this location. Overall, however, this information is relatively blurry and the electrosense exhibits relatively poor acuity. Despite this apparent limitation, weakly electric fish are able to extract the minute signals generated by small prey, even in the presence of large background signals. In fact, we show that the fish's poor spatial acuity may actually enhance prey detection under some conditions. This occurs because the electric image produced by a spatially dense background is relatively "blurred" or spatially uniform. Hence, the small spatially localized prey signal "pops out" when fish motion is simulated. This shows explicitly how the back-and-forth swimming, characteristic of these fish, can be used to generate motion cues that, as in other animals, assist in the extraction of sensory information when signal-to-noise ratios are low. Our study also reveals the importance of the structure of complex electrosensory backgrounds. Whereas large-object spacing is favorable for discriminating the individual elements of a scene, small spacing can increase the fish's ability to resolve a single target object against this background.

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Effect of Object Location and Conductivity on Spatial ElectroacuityIn all panels, see fish insets for approximate lateral and rostro–caudal locations where Smin was calculated. Error bars represent the sampling that was used to calculate the Smin (either 0.5 or 1 mm). Lateral distance is measured as object center to fish skin (as in Figure 1).(A) Effect of lateral distance on Smin for three distinct object diameters (rostro–caudal location, x = 0.11 m). Red, 0.3 cm (prey size); green, 1 cm; blue, 2 cm. Object conductivity fixed at 0.0303 S/m (prey conductivity).(B) Effect of rostro–caudal position on Smin for same object sizes and conductivity as (A), with a lateral distance of 0.012 m.(C) Effect of lateral distance on Smin for three distinct object conductivities (rostro–caudal location, x = 0.11m). Red, 0.0005 S/m (plant conductivity); green, 0.0303 S/m (prey conductivity); blue, 0.5 S/m. Object diameters fixed at 0.3 cm (prey size).(D) Effect of rostro–caudal position on Smin for same object diameter and conductivities as in (C), with a lateral distance of 0.012 m.
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pcbi-0030038-g002: Effect of Object Location and Conductivity on Spatial ElectroacuityIn all panels, see fish insets for approximate lateral and rostro–caudal locations where Smin was calculated. Error bars represent the sampling that was used to calculate the Smin (either 0.5 or 1 mm). Lateral distance is measured as object center to fish skin (as in Figure 1).(A) Effect of lateral distance on Smin for three distinct object diameters (rostro–caudal location, x = 0.11 m). Red, 0.3 cm (prey size); green, 1 cm; blue, 2 cm. Object conductivity fixed at 0.0303 S/m (prey conductivity).(B) Effect of rostro–caudal position on Smin for same object sizes and conductivity as (A), with a lateral distance of 0.012 m.(C) Effect of lateral distance on Smin for three distinct object conductivities (rostro–caudal location, x = 0.11m). Red, 0.0005 S/m (plant conductivity); green, 0.0303 S/m (prey conductivity); blue, 0.5 S/m. Object diameters fixed at 0.3 cm (prey size).(D) Effect of rostro–caudal position on Smin for same object diameter and conductivities as in (C), with a lateral distance of 0.012 m.

Mentions: Electroacuity varies for different lateral and rostro–caudal object locations (Figure 2, see insets). Figure 2A and 2C shows the effects of object size and conductivity, respectively, on electroacuity for different lateral positions (rostro–caudal position fixed near the fish's midpoint, 0.11 m). Smin increases (electroacuity decreases) for objects that are placed farther away from the fish, regardless of object size or conductivity. When objects are far from the fish, Smin is roughly independent of object size (Figure 2A). At the closest location possible for the largest object (blue curve), Smin is smaller than for the other object sizes. This is a consequence of the relative sharpening of the image for close large objects (see Figure 1B). The sharpness of an image can be quantified by the reciprocal of its normalized width (width divided by amplitude). Image sharpness decreases (normalized width increases) with lateral distance and, in general, is independent of object size [5]. However, object size becomes a factor for locations close to the skin (see largest object in Figure 2A and 2B), as larger objects produce relatively sharper images in these cases [9]. Note also that there is a slight inflection at a lateral distance of 0.016 m (Figure 2A and 2C) due to the spatial heterogeneity of the electric field (higher density of field lines near the zero potential line, which curves rostrally as seen in Figure 1A).


Spatial acuity and prey detection in weakly electric fish.

Babineau D, Lewis JE, Longtin A - PLoS Comput. Biol. (2007)

Effect of Object Location and Conductivity on Spatial ElectroacuityIn all panels, see fish insets for approximate lateral and rostro–caudal locations where Smin was calculated. Error bars represent the sampling that was used to calculate the Smin (either 0.5 or 1 mm). Lateral distance is measured as object center to fish skin (as in Figure 1).(A) Effect of lateral distance on Smin for three distinct object diameters (rostro–caudal location, x = 0.11 m). Red, 0.3 cm (prey size); green, 1 cm; blue, 2 cm. Object conductivity fixed at 0.0303 S/m (prey conductivity).(B) Effect of rostro–caudal position on Smin for same object sizes and conductivity as (A), with a lateral distance of 0.012 m.(C) Effect of lateral distance on Smin for three distinct object conductivities (rostro–caudal location, x = 0.11m). Red, 0.0005 S/m (plant conductivity); green, 0.0303 S/m (prey conductivity); blue, 0.5 S/m. Object diameters fixed at 0.3 cm (prey size).(D) Effect of rostro–caudal position on Smin for same object diameter and conductivities as in (C), with a lateral distance of 0.012 m.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC1808493&req=5

pcbi-0030038-g002: Effect of Object Location and Conductivity on Spatial ElectroacuityIn all panels, see fish insets for approximate lateral and rostro–caudal locations where Smin was calculated. Error bars represent the sampling that was used to calculate the Smin (either 0.5 or 1 mm). Lateral distance is measured as object center to fish skin (as in Figure 1).(A) Effect of lateral distance on Smin for three distinct object diameters (rostro–caudal location, x = 0.11 m). Red, 0.3 cm (prey size); green, 1 cm; blue, 2 cm. Object conductivity fixed at 0.0303 S/m (prey conductivity).(B) Effect of rostro–caudal position on Smin for same object sizes and conductivity as (A), with a lateral distance of 0.012 m.(C) Effect of lateral distance on Smin for three distinct object conductivities (rostro–caudal location, x = 0.11m). Red, 0.0005 S/m (plant conductivity); green, 0.0303 S/m (prey conductivity); blue, 0.5 S/m. Object diameters fixed at 0.3 cm (prey size).(D) Effect of rostro–caudal position on Smin for same object diameter and conductivities as in (C), with a lateral distance of 0.012 m.
Mentions: Electroacuity varies for different lateral and rostro–caudal object locations (Figure 2, see insets). Figure 2A and 2C shows the effects of object size and conductivity, respectively, on electroacuity for different lateral positions (rostro–caudal position fixed near the fish's midpoint, 0.11 m). Smin increases (electroacuity decreases) for objects that are placed farther away from the fish, regardless of object size or conductivity. When objects are far from the fish, Smin is roughly independent of object size (Figure 2A). At the closest location possible for the largest object (blue curve), Smin is smaller than for the other object sizes. This is a consequence of the relative sharpening of the image for close large objects (see Figure 1B). The sharpness of an image can be quantified by the reciprocal of its normalized width (width divided by amplitude). Image sharpness decreases (normalized width increases) with lateral distance and, in general, is independent of object size [5]. However, object size becomes a factor for locations close to the skin (see largest object in Figure 2A and 2B), as larger objects produce relatively sharper images in these cases [9]. Note also that there is a slight inflection at a lateral distance of 0.016 m (Figure 2A and 2C) due to the spatial heterogeneity of the electric field (higher density of field lines near the zero potential line, which curves rostrally as seen in Figure 1A).

Bottom Line: This shows explicitly how the back-and-forth swimming, characteristic of these fish, can be used to generate motion cues that, as in other animals, assist in the extraction of sensory information when signal-to-noise ratios are low.Our study also reveals the importance of the structure of complex electrosensory backgrounds.Whereas large-object spacing is favorable for discriminating the individual elements of a scene, small spacing can increase the fish's ability to resolve a single target object against this background.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, University of Ottawa, Ottawa, Ontario, Canada.

ABSTRACT
It is well-known that weakly electric fish can exhibit extreme temporal acuity at the behavioral level, discriminating time intervals in the submicrosecond range. However, relatively little is known about the spatial acuity of the electrosense. Here we use a recently developed model of the electric field generated by Apteronotus leptorhynchus to study spatial acuity and small signal extraction. We show that the quality of sensory information available on the lateral body surface is highest for objects close to the fish's midbody, suggesting that spatial acuity should be highest at this location. Overall, however, this information is relatively blurry and the electrosense exhibits relatively poor acuity. Despite this apparent limitation, weakly electric fish are able to extract the minute signals generated by small prey, even in the presence of large background signals. In fact, we show that the fish's poor spatial acuity may actually enhance prey detection under some conditions. This occurs because the electric image produced by a spatially dense background is relatively "blurred" or spatially uniform. Hence, the small spatially localized prey signal "pops out" when fish motion is simulated. This shows explicitly how the back-and-forth swimming, characteristic of these fish, can be used to generate motion cues that, as in other animals, assist in the extraction of sensory information when signal-to-noise ratios are low. Our study also reveals the importance of the structure of complex electrosensory backgrounds. Whereas large-object spacing is favorable for discriminating the individual elements of a scene, small spacing can increase the fish's ability to resolve a single target object against this background.

Show MeSH
Related in: MedlinePlus