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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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Prey Detectibility and Background Sparseness(Left axis, blue trace) SNR ratio between the prey and background transdermal potential time series and the background-only time series (i.e., between blue and green traces in Figure 5A; see Materials and Methods for more details). Each point represents the mean SNR of ten locations (over an ~0.01 m–wide patch of skin) centered 0.05 m caudal from the tip of the fish's head. SNR is shown as a function of interobject spacing of the background.(Right axis, green trace) Theoretical discriminability (see Materials and Methods) between two background-type objects as a function of their spacing, using the same object size (2-cm diameter) and lateral distance (0.05 m) as in Figure 5.
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pcbi-0030038-g006: Prey Detectibility and Background Sparseness(Left axis, blue trace) SNR ratio between the prey and background transdermal potential time series and the background-only time series (i.e., between blue and green traces in Figure 5A; see Materials and Methods for more details). Each point represents the mean SNR of ten locations (over an ~0.01 m–wide patch of skin) centered 0.05 m caudal from the tip of the fish's head. SNR is shown as a function of interobject spacing of the background.(Right axis, green trace) Theoretical discriminability (see Materials and Methods) between two background-type objects as a function of their spacing, using the same object size (2-cm diameter) and lateral distance (0.05 m) as in Figure 5.

Mentions: Figure 5A and 5B suggests that as the objects within the background are increasingly separated, the prey will be less distinguishable. We confirm these observations in terms of a signal-to-noise ratio (SNR) of prey signal versus background (see Materials and Methods). The SNR decreases with increasing interobject separation in the background (Figure 6; left axis, blue trace). For reference, we can compare this situation with the expected discriminability of two individual objects (see Materials and Methods), where the electric image components due to each object become increasingly distinct as the objects are moved apart (Figure 1B; Figure 5C: right axis, green trace). This applies to the case of two prey-like objects in the absence of background, as in Figure 1A and 1C and Figure 2, as well as to the case of two background-like objects. In a more natural context, the blurriness of the electrosense interestingly has the effect of enhancing sensory performance. And indeed, this should apply to a wide range of electrosensory landscapes, as blurriness will be unaffected by small changes in object conductivity (Figure 2C and 2D).


Spatial acuity and prey detection in weakly electric fish.

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

Prey Detectibility and Background Sparseness(Left axis, blue trace) SNR ratio between the prey and background transdermal potential time series and the background-only time series (i.e., between blue and green traces in Figure 5A; see Materials and Methods for more details). Each point represents the mean SNR of ten locations (over an ~0.01 m–wide patch of skin) centered 0.05 m caudal from the tip of the fish's head. SNR is shown as a function of interobject spacing of the background.(Right axis, green trace) Theoretical discriminability (see Materials and Methods) between two background-type objects as a function of their spacing, using the same object size (2-cm diameter) and lateral distance (0.05 m) as in Figure 5.
© Copyright Policy
Related In: Results  -  Collection

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

pcbi-0030038-g006: Prey Detectibility and Background Sparseness(Left axis, blue trace) SNR ratio between the prey and background transdermal potential time series and the background-only time series (i.e., between blue and green traces in Figure 5A; see Materials and Methods for more details). Each point represents the mean SNR of ten locations (over an ~0.01 m–wide patch of skin) centered 0.05 m caudal from the tip of the fish's head. SNR is shown as a function of interobject spacing of the background.(Right axis, green trace) Theoretical discriminability (see Materials and Methods) between two background-type objects as a function of their spacing, using the same object size (2-cm diameter) and lateral distance (0.05 m) as in Figure 5.
Mentions: Figure 5A and 5B suggests that as the objects within the background are increasingly separated, the prey will be less distinguishable. We confirm these observations in terms of a signal-to-noise ratio (SNR) of prey signal versus background (see Materials and Methods). The SNR decreases with increasing interobject separation in the background (Figure 6; left axis, blue trace). For reference, we can compare this situation with the expected discriminability of two individual objects (see Materials and Methods), where the electric image components due to each object become increasingly distinct as the objects are moved apart (Figure 1B; Figure 5C: right axis, green trace). This applies to the case of two prey-like objects in the absence of background, as in Figure 1A and 1C and Figure 2, as well as to the case of two background-like objects. In a more natural context, the blurriness of the electrosense interestingly has the effect of enhancing sensory performance. And indeed, this should apply to a wide range of electrosensory landscapes, as blurriness will be unaffected by small changes in object conductivity (Figure 2C and 2D).

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