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Information generated by the moving pinnae of Rhinolophus rouxi: tuning of the morphology at different harmonics.

Vanderelst D, Reijniers J, Steckel J, Peremans H - PLoS ONE (2011)

Bottom Line: In contrast, using the 1st overtone, it can only locate objects, albeit with a slightly higher accuracy, in a small portion of the frontal hemisphere by reducing sensitivity to echoes from outside this region of interest.We propose these findings can be interpreted in the context of the foraging behaviour of R. rouxi, i.e., hunting in cluttered environments.Indeed, the focused view provided by the 1st overtone suggests that at this frequency its morphology is tuned for clutter rejection and accurate localization in a small region of interest while the finding that overall localization performance is best at the fundamental indicates that the morphology is simultaneously tuned to optimize overall localization performance at this frequency.

View Article: PubMed Central - PubMed

Affiliation: Department MTT-FTEW, Active Perception Lab, University Antwerp, Antwerp, Belgium. dieter.vanderelst@ua.ac.be

ABSTRACT
Bats typically emit multi harmonic calls. Their head morphology shapes the emission and hearing sound fields as a function of frequency. Therefore, the sound fields are markedly different for the various harmonics. As the sound field provides bats with all necessary cues to locate objects in space, different harmonics might provide them with variable amounts of information about the location of objects. Also, the ability to locate objects in different parts of the frontal hemisphere might vary across harmonics. This paper evaluates this hypothesis in R. rouxi, using an information theoretic framework. We estimate the reflector position information transfer in the echolocation system of R. rouxi as a function of frequency. This analysis shows that localization performance reaches a global minimum and a global maximum at the two most energetic frequency components of R. rouxi call indicating tuning of morphology and harmonic structure. Using the fundamental the bat is able to locate objects in a large portion of the frontal hemisphere. In contrast, using the 1st overtone, it can only locate objects, albeit with a slightly higher accuracy, in a small portion of the frontal hemisphere by reducing sensitivity to echoes from outside this region of interest. Hence, different harmonic components provide the bat either with a wide view or a focused view of its environment. We propose these findings can be interpreted in the context of the foraging behaviour of R. rouxi, i.e., hunting in cluttered environments. Indeed, the focused view provided by the 1st overtone suggests that at this frequency its morphology is tuned for clutter rejection and accurate localization in a small region of interest while the finding that overall localization performance is best at the fundamental indicates that the morphology is simultaneously tuned to optimize overall localization performance at this frequency.

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Related in: MedlinePlus

Results of the Monte Carlo simulation of perch hunting.(a) The average entropy about the location of an insect as function of the used echolocation frequency and the distance between the bat and the insect (which determines the echo strength) as established by a Monte Carlo simulation. (b) Similar as (a) but for the model in which the emission pattern of R. rouxi was replaced by that of two isotropic sources. (c) Difference between (a) and (b). Note that the scale of the y-axis is different in (c). The yellow regions are 95% confidence ranges for the fundamental and 1 overtone in the call of R. rouxi as estimated from ref. [8].
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pone-0020627-g007: Results of the Monte Carlo simulation of perch hunting.(a) The average entropy about the location of an insect as function of the used echolocation frequency and the distance between the bat and the insect (which determines the echo strength) as established by a Monte Carlo simulation. (b) Similar as (a) but for the model in which the emission pattern of R. rouxi was replaced by that of two isotropic sources. (c) Difference between (a) and (b). Note that the scale of the y-axis is different in (c). The yellow regions are 95% confidence ranges for the fundamental and 1 overtone in the call of R. rouxi as estimated from ref. [8].

Mentions: Figure 7a, shows that when including the parameters known about the behavior of R. rouxi, the tuning of the echolocation system for frequencies little below 40 kHz is confirmed. The curves in this figure reach a minimum around the fundamental. Moreover, the lack in performance around 80 kHz is also shown as the performance reaches a lower plateau around this frequency. Indeed, performance reaches a global minimum around 80 kHz and performance does not increases for higher frequencies. It is the atmospheric attenuation for higher frequencies that prevents performance to increase for frequencies above 80 kHz (as was the case in figure 5 were atmospheric attenuation was not taken into account).


Information generated by the moving pinnae of Rhinolophus rouxi: tuning of the morphology at different harmonics.

Vanderelst D, Reijniers J, Steckel J, Peremans H - PLoS ONE (2011)

Results of the Monte Carlo simulation of perch hunting.(a) The average entropy about the location of an insect as function of the used echolocation frequency and the distance between the bat and the insect (which determines the echo strength) as established by a Monte Carlo simulation. (b) Similar as (a) but for the model in which the emission pattern of R. rouxi was replaced by that of two isotropic sources. (c) Difference between (a) and (b). Note that the scale of the y-axis is different in (c). The yellow regions are 95% confidence ranges for the fundamental and 1 overtone in the call of R. rouxi as estimated from ref. [8].
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3117793&req=5

pone-0020627-g007: Results of the Monte Carlo simulation of perch hunting.(a) The average entropy about the location of an insect as function of the used echolocation frequency and the distance between the bat and the insect (which determines the echo strength) as established by a Monte Carlo simulation. (b) Similar as (a) but for the model in which the emission pattern of R. rouxi was replaced by that of two isotropic sources. (c) Difference between (a) and (b). Note that the scale of the y-axis is different in (c). The yellow regions are 95% confidence ranges for the fundamental and 1 overtone in the call of R. rouxi as estimated from ref. [8].
Mentions: Figure 7a, shows that when including the parameters known about the behavior of R. rouxi, the tuning of the echolocation system for frequencies little below 40 kHz is confirmed. The curves in this figure reach a minimum around the fundamental. Moreover, the lack in performance around 80 kHz is also shown as the performance reaches a lower plateau around this frequency. Indeed, performance reaches a global minimum around 80 kHz and performance does not increases for higher frequencies. It is the atmospheric attenuation for higher frequencies that prevents performance to increase for frequencies above 80 kHz (as was the case in figure 5 were atmospheric attenuation was not taken into account).

Bottom Line: In contrast, using the 1st overtone, it can only locate objects, albeit with a slightly higher accuracy, in a small portion of the frontal hemisphere by reducing sensitivity to echoes from outside this region of interest.We propose these findings can be interpreted in the context of the foraging behaviour of R. rouxi, i.e., hunting in cluttered environments.Indeed, the focused view provided by the 1st overtone suggests that at this frequency its morphology is tuned for clutter rejection and accurate localization in a small region of interest while the finding that overall localization performance is best at the fundamental indicates that the morphology is simultaneously tuned to optimize overall localization performance at this frequency.

View Article: PubMed Central - PubMed

Affiliation: Department MTT-FTEW, Active Perception Lab, University Antwerp, Antwerp, Belgium. dieter.vanderelst@ua.ac.be

ABSTRACT
Bats typically emit multi harmonic calls. Their head morphology shapes the emission and hearing sound fields as a function of frequency. Therefore, the sound fields are markedly different for the various harmonics. As the sound field provides bats with all necessary cues to locate objects in space, different harmonics might provide them with variable amounts of information about the location of objects. Also, the ability to locate objects in different parts of the frontal hemisphere might vary across harmonics. This paper evaluates this hypothesis in R. rouxi, using an information theoretic framework. We estimate the reflector position information transfer in the echolocation system of R. rouxi as a function of frequency. This analysis shows that localization performance reaches a global minimum and a global maximum at the two most energetic frequency components of R. rouxi call indicating tuning of morphology and harmonic structure. Using the fundamental the bat is able to locate objects in a large portion of the frontal hemisphere. In contrast, using the 1st overtone, it can only locate objects, albeit with a slightly higher accuracy, in a small portion of the frontal hemisphere by reducing sensitivity to echoes from outside this region of interest. Hence, different harmonic components provide the bat either with a wide view or a focused view of its environment. We propose these findings can be interpreted in the context of the foraging behaviour of R. rouxi, i.e., hunting in cluttered environments. Indeed, the focused view provided by the 1st overtone suggests that at this frequency its morphology is tuned for clutter rejection and accurate localization in a small region of interest while the finding that overall localization performance is best at the fundamental indicates that the morphology is simultaneously tuned to optimize overall localization performance at this frequency.

Show MeSH
Related in: MedlinePlus