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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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Localization performance as a function frequency.Higher values denote higher entropy and lower localization performance. (a) The performance of the model for different signal to noise ratios as a function of frequency for a medium noise level averaged across the frontal hemisphere (see Methods section). (b) The performance as a function of frequency averaged across the signal to noise ratios for three levels of noise and a model in which the emission pattern was replaced by that of two isotropic sound sources. (c) The difference between the azimuth-elevation position for which performance is the worst and the best as function of frequency. This plot shows that, at around 80 kHz, the range in localization performance across the frontal hemisphere is the largest. Moreover, the range in performance across locations in the frontal hemisphere is reduced by replacing the emission pattern of R. rouxi by that of two isotropic sources. The yellow regions are 95% confidence ranges for the fundamental and 1 overtone in the call of R. rouxi as estimated from the data provided in ref. [8].
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pone-0020627-g005: Localization performance as a function frequency.Higher values denote higher entropy and lower localization performance. (a) The performance of the model for different signal to noise ratios as a function of frequency for a medium noise level averaged across the frontal hemisphere (see Methods section). (b) The performance as a function of frequency averaged across the signal to noise ratios for three levels of noise and a model in which the emission pattern was replaced by that of two isotropic sound sources. (c) The difference between the azimuth-elevation position for which performance is the worst and the best as function of frequency. This plot shows that, at around 80 kHz, the range in localization performance across the frontal hemisphere is the largest. Moreover, the range in performance across locations in the frontal hemisphere is reduced by replacing the emission pattern of R. rouxi by that of two isotropic sources. The yellow regions are 95% confidence ranges for the fundamental and 1 overtone in the call of R. rouxi as estimated from the data provided in ref. [8].

Mentions: In figure 5a, the average performance of the model in the frontal hemisphere is plotted as a function of frequency and echo strength. The curves tend to show a minimum around 40 kHz (i.e. at the fundamental) while they reach a maximum around 80 kHz (i.e. at the 1 overtone). Indeed, when averaging across echo strengths (figure 5b), it can be seen that the model performs best slightly below 40 kHz and worst slightly below 80 kHz. The reason for the good performance at 40 kHz and the bad performance at 80 kHz can be understood by looking at the properties of the templates at these frequencies (figure 6).


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)

Localization performance as a function frequency.Higher values denote higher entropy and lower localization performance. (a) The performance of the model for different signal to noise ratios as a function of frequency for a medium noise level averaged across the frontal hemisphere (see Methods section). (b) The performance as a function of frequency averaged across the signal to noise ratios for three levels of noise and a model in which the emission pattern was replaced by that of two isotropic sound sources. (c) The difference between the azimuth-elevation position for which performance is the worst and the best as function of frequency. This plot shows that, at around 80 kHz, the range in localization performance across the frontal hemisphere is the largest. Moreover, the range in performance across locations in the frontal hemisphere is reduced by replacing the emission pattern of R. rouxi by that of two isotropic sources. The yellow regions are 95% confidence ranges for the fundamental and 1 overtone in the call of R. rouxi as estimated from the data provided in ref. [8].
© Copyright Policy
Related In: Results  -  Collection

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

pone-0020627-g005: Localization performance as a function frequency.Higher values denote higher entropy and lower localization performance. (a) The performance of the model for different signal to noise ratios as a function of frequency for a medium noise level averaged across the frontal hemisphere (see Methods section). (b) The performance as a function of frequency averaged across the signal to noise ratios for three levels of noise and a model in which the emission pattern was replaced by that of two isotropic sound sources. (c) The difference between the azimuth-elevation position for which performance is the worst and the best as function of frequency. This plot shows that, at around 80 kHz, the range in localization performance across the frontal hemisphere is the largest. Moreover, the range in performance across locations in the frontal hemisphere is reduced by replacing the emission pattern of R. rouxi by that of two isotropic sources. The yellow regions are 95% confidence ranges for the fundamental and 1 overtone in the call of R. rouxi as estimated from the data provided in ref. [8].
Mentions: In figure 5a, the average performance of the model in the frontal hemisphere is plotted as a function of frequency and echo strength. The curves tend to show a minimum around 40 kHz (i.e. at the fundamental) while they reach a maximum around 80 kHz (i.e. at the 1 overtone). Indeed, when averaging across echo strengths (figure 5b), it can be seen that the model performs best slightly below 40 kHz and worst slightly below 80 kHz. The reason for the good performance at 40 kHz and the bad performance at 80 kHz can be understood by looking at the properties of the templates at these frequencies (figure 6).

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