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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

Illustration of the classification model used to evaluate the localization performance of R. rouxi.Top row: (a) Targets at different locations (red and green insect) yield a similar echo (b) of which the amplitude is modulated due to movements of the targets. The movement of the pinnae (c) during the reception of the echo modulates the amplitude of the echo (d). This modulation depends on how the pinna movement moves the target through the HRTF of R. rouxi (illustrated in c bottom). (d) The final amplitude modulated echoes for the read and the green target at both tympanic membranes. Bottom Row: An algorithmic explanation of the model. The direction from which an echo originates is encoded by the amplitude modulation introduced by the ears (templates). Distortions of this encoding occur due to amplitude modulations introduced by the moving targets. The bat tries to decode the direction of the echo. Our model estimates the mutual information between the echo and the echo direction.
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pone-0020627-g002: Illustration of the classification model used to evaluate the localization performance of R. rouxi.Top row: (a) Targets at different locations (red and green insect) yield a similar echo (b) of which the amplitude is modulated due to movements of the targets. The movement of the pinnae (c) during the reception of the echo modulates the amplitude of the echo (d). This modulation depends on how the pinna movement moves the target through the HRTF of R. rouxi (illustrated in c bottom). (d) The final amplitude modulated echoes for the read and the green target at both tympanic membranes. Bottom Row: An algorithmic explanation of the model. The direction from which an echo originates is encoded by the amplitude modulation introduced by the ears (templates). Distortions of this encoding occur due to amplitude modulations introduced by the moving targets. The bat tries to decode the direction of the echo. Our model estimates the mutual information between the echo and the echo direction.

Mentions: To evaluate the contributions of the harmonics in the calls of R. rouxi we employ an information theoretic model of the echolocation task as illustrated in figure 2. The basic assumption of this model is that localization of a target can be considered as a template matching task [7], [23], [24].


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)

Illustration of the classification model used to evaluate the localization performance of R. rouxi.Top row: (a) Targets at different locations (red and green insect) yield a similar echo (b) of which the amplitude is modulated due to movements of the targets. The movement of the pinnae (c) during the reception of the echo modulates the amplitude of the echo (d). This modulation depends on how the pinna movement moves the target through the HRTF of R. rouxi (illustrated in c bottom). (d) The final amplitude modulated echoes for the read and the green target at both tympanic membranes. Bottom Row: An algorithmic explanation of the model. The direction from which an echo originates is encoded by the amplitude modulation introduced by the ears (templates). Distortions of this encoding occur due to amplitude modulations introduced by the moving targets. The bat tries to decode the direction of the echo. Our model estimates the mutual information between the echo and the echo direction.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0020627-g002: Illustration of the classification model used to evaluate the localization performance of R. rouxi.Top row: (a) Targets at different locations (red and green insect) yield a similar echo (b) of which the amplitude is modulated due to movements of the targets. The movement of the pinnae (c) during the reception of the echo modulates the amplitude of the echo (d). This modulation depends on how the pinna movement moves the target through the HRTF of R. rouxi (illustrated in c bottom). (d) The final amplitude modulated echoes for the read and the green target at both tympanic membranes. Bottom Row: An algorithmic explanation of the model. The direction from which an echo originates is encoded by the amplitude modulation introduced by the ears (templates). Distortions of this encoding occur due to amplitude modulations introduced by the moving targets. The bat tries to decode the direction of the echo. Our model estimates the mutual information between the echo and the echo direction.
Mentions: To evaluate the contributions of the harmonics in the calls of R. rouxi we employ an information theoretic model of the echolocation task as illustrated in figure 2. The basic assumption of this model is that localization of a target can be considered as a template matching task [7], [23], [24].

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