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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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Electric Image of a Plant-Like Background in the Presence and Absence of a Prey ObjectAll images in both panels are computed as the difference in transdermal potentials, with and without objects (as described in Materials and Methods).(A) Six fish positions (see inset, top) for which the electric images (bottom) produced by a 15-disc Hygrophilia plant-like background (0.05 m lateral to fish, as in Figure 3) were calculated. Electric images are barely distinguishable from one another. Fish positions differ from one another by 0.02 m, 0.02 m, 0.03 m, 0.005 m, and 0.015 m (see inset).(B) Same as in panel (A) except a Daphnia-like prey object (0.3-cm diameter as in Figure 1) was added at a lateral distance of 0.008 m from the skin.
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pcbi-0030038-g004: Electric Image of a Plant-Like Background in the Presence and Absence of a Prey ObjectAll images in both panels are computed as the difference in transdermal potentials, with and without objects (as described in Materials and Methods).(A) Six fish positions (see inset, top) for which the electric images (bottom) produced by a 15-disc Hygrophilia plant-like background (0.05 m lateral to fish, as in Figure 3) were calculated. Electric images are barely distinguishable from one another. Fish positions differ from one another by 0.02 m, 0.02 m, 0.03 m, 0.005 m, and 0.015 m (see inset).(B) Same as in panel (A) except a Daphnia-like prey object (0.3-cm diameter as in Figure 1) was added at a lateral distance of 0.008 m from the skin.

Mentions: These object arrays provide a simplified model of the background signals comprising a natural electrosensory landscape. To better understand how weakly electric fish are able to detect miniscule prey in the presence of large-background signals, we calculated the electric image produced by a small Daphnia-like prey object against a large-background array of objects (Figure 4). Even though the prey is located just 0.008 m from the fish's skin (compared with the 0.05 m lateral position of the background), the electric image with the prey and background is not much different than the one obtained with the background alone (largest deviation between the two images is about 4%; compare Figure 4A and 4B). The interesting feature, however, is that the overall image shape is similar regardless of the fish's position during a simulated scanning movement (even though the background was simulated as a discrete set of objects). This can be understood in terms of electroacuity: the background objects are too close together to be distinguished and thus form a blurred image. It is critical to note that during the scan, however, the small blip created by the prey does change location within the electric image (Figure 4B; note that the images do not overlap perfectly). Next, we demonstrate this point explicitly by considering the time-varying image during a simulated scanning movement.


Spatial acuity and prey detection in weakly electric fish.

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

Electric Image of a Plant-Like Background in the Presence and Absence of a Prey ObjectAll images in both panels are computed as the difference in transdermal potentials, with and without objects (as described in Materials and Methods).(A) Six fish positions (see inset, top) for which the electric images (bottom) produced by a 15-disc Hygrophilia plant-like background (0.05 m lateral to fish, as in Figure 3) were calculated. Electric images are barely distinguishable from one another. Fish positions differ from one another by 0.02 m, 0.02 m, 0.03 m, 0.005 m, and 0.015 m (see inset).(B) Same as in panel (A) except a Daphnia-like prey object (0.3-cm diameter as in Figure 1) was added at a lateral distance of 0.008 m from the skin.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1808493&req=5

pcbi-0030038-g004: Electric Image of a Plant-Like Background in the Presence and Absence of a Prey ObjectAll images in both panels are computed as the difference in transdermal potentials, with and without objects (as described in Materials and Methods).(A) Six fish positions (see inset, top) for which the electric images (bottom) produced by a 15-disc Hygrophilia plant-like background (0.05 m lateral to fish, as in Figure 3) were calculated. Electric images are barely distinguishable from one another. Fish positions differ from one another by 0.02 m, 0.02 m, 0.03 m, 0.005 m, and 0.015 m (see inset).(B) Same as in panel (A) except a Daphnia-like prey object (0.3-cm diameter as in Figure 1) was added at a lateral distance of 0.008 m from the skin.
Mentions: These object arrays provide a simplified model of the background signals comprising a natural electrosensory landscape. To better understand how weakly electric fish are able to detect miniscule prey in the presence of large-background signals, we calculated the electric image produced by a small Daphnia-like prey object against a large-background array of objects (Figure 4). Even though the prey is located just 0.008 m from the fish's skin (compared with the 0.05 m lateral position of the background), the electric image with the prey and background is not much different than the one obtained with the background alone (largest deviation between the two images is about 4%; compare Figure 4A and 4B). The interesting feature, however, is that the overall image shape is similar regardless of the fish's position during a simulated scanning movement (even though the background was simulated as a discrete set of objects). This can be understood in terms of electroacuity: the background objects are too close together to be distinguished and thus form a blurred image. It is critical to note that during the scan, however, the small blip created by the prey does change location within the electric image (Figure 4B; note that the images do not overlap perfectly). Next, we demonstrate this point explicitly by considering the time-varying image during a simulated scanning movement.

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