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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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Results of measurements performed to estimate the parameter settings of the model.(a) The standard deviation of the spectral power of echoes from a fluttering locust at 40 and 80 kHz for five directions of ensonification. (b) The correlation between the magnitude of echoes from a fluttering locust as a function of the time between the collection of the echoes for 6 different frequencies (averaged across direction from which the insect was ensonified).
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pone-0020627-g008: Results of measurements performed to estimate the parameter settings of the model.(a) The standard deviation of the spectral power of echoes from a fluttering locust at 40 and 80 kHz for five directions of ensonification. (b) The correlation between the magnitude of echoes from a fluttering locust as a function of the time between the collection of the echoes for 6 different frequencies (averaged across direction from which the insect was ensonified).

Mentions: As outlined above, the model has only one free parameter, the covariance matrix . This matrix models the unknown amplitude modulations of the received echo due to target fluttering.(11)with and denoting the -th position of the left and the right ear respectively. In our simulations, . As can be seen from equation 11, three types of covariance values need to be filled in in this matrix. First, the variation for each of the positions of the two pinnae, and . To obtain an estimate of this variance we ensonified a fluttering locust (Locusta migratoria, body length about 6 cm). The locust was attached in front of a Polaroid ultrasonic emitter. The distance between the locust and the emitter was 45 cm. The insect was ensonified using an hyperbolic FM sweep from 100 to 30 kHz, duration 1.5 ms. The fluttering locust was ensonified in batches of 400 calls with an interpulse interval of 6 ms yielding a repetition rate of about 166 Herz. The locust was ensonified from 5 different aspect angles to verify whether the estimation of is aspect angle independent (see table 1). A Knowles microphone (Knowles Electronics, Itasca, IL, USA, FG23329) was mounted on top of the Polaroid emitter. For each angle, at least 20 batches of 400 measurements are collected, yielding a minimum of 8000 echoes. For each echo we extracted the spectral power at 40 and 80 kHz using the Goertzel algorithm. We calculated the standard deviation of the spectral power at these frequencies for each of the 5 positions from which the locust was ensonified. For the 5 positions and the 2 frequencies, the standard deviation of the gain was about 5 . (figure 8). Therefore, we used 5 as the default value for the diagonal elements of . However, we also evaluated the model for and . In the results presented above, we have labeled , and as Low, Medium and High noise respectively.


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 measurements performed to estimate the parameter settings of the model.(a) The standard deviation of the spectral power of echoes from a fluttering locust at 40 and 80 kHz for five directions of ensonification. (b) The correlation between the magnitude of echoes from a fluttering locust as a function of the time between the collection of the echoes for 6 different frequencies (averaged across direction from which the insect was ensonified).
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3117793&req=5

pone-0020627-g008: Results of measurements performed to estimate the parameter settings of the model.(a) The standard deviation of the spectral power of echoes from a fluttering locust at 40 and 80 kHz for five directions of ensonification. (b) The correlation between the magnitude of echoes from a fluttering locust as a function of the time between the collection of the echoes for 6 different frequencies (averaged across direction from which the insect was ensonified).
Mentions: As outlined above, the model has only one free parameter, the covariance matrix . This matrix models the unknown amplitude modulations of the received echo due to target fluttering.(11)with and denoting the -th position of the left and the right ear respectively. In our simulations, . As can be seen from equation 11, three types of covariance values need to be filled in in this matrix. First, the variation for each of the positions of the two pinnae, and . To obtain an estimate of this variance we ensonified a fluttering locust (Locusta migratoria, body length about 6 cm). The locust was attached in front of a Polaroid ultrasonic emitter. The distance between the locust and the emitter was 45 cm. The insect was ensonified using an hyperbolic FM sweep from 100 to 30 kHz, duration 1.5 ms. The fluttering locust was ensonified in batches of 400 calls with an interpulse interval of 6 ms yielding a repetition rate of about 166 Herz. The locust was ensonified from 5 different aspect angles to verify whether the estimation of is aspect angle independent (see table 1). A Knowles microphone (Knowles Electronics, Itasca, IL, USA, FG23329) was mounted on top of the Polaroid emitter. For each angle, at least 20 batches of 400 measurements are collected, yielding a minimum of 8000 echoes. For each echo we extracted the spectral power at 40 and 80 kHz using the Goertzel algorithm. We calculated the standard deviation of the spectral power at these frequencies for each of the 5 positions from which the locust was ensonified. For the 5 positions and the 2 frequencies, the standard deviation of the gain was about 5 . (figure 8). Therefore, we used 5 as the default value for the diagonal elements of . However, we also evaluated the model for and . In the results presented above, we have labeled , and as Low, Medium and High noise respectively.

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