Bats have excellent spatial memory and can navigate with ease to familiar locations including roosts and foraging grounds. We know they can recognize these places through echolocation, but how they do it is largely unknown.
According to new research from the Universities of Bristol and Antwerp, it’s possible the animals form a cognitive map of their environment by observing and memorizing templates.
“When we visually recognize places, such as our living room or office, we identify and localize the various objects that make up the scene,” says Marc Holderied, PhD, Reader in Biology at the University of Bristol, and senior author of the study published in the journal eLife. “Echolocation does not allow bats to do this, as the information it provides is more limited. We therefore wanted to discover how these animals recognize their locations differently to those with vision.”
The team proposed that template-based place recognition might underlie sonar-based navigation in bats, meaning the animals are able to recognize places by remembering their echo signature, rather than their three-dimensional layout.
“The viability of a template-based approach to place recognition relies on two properties. One of these is that templates must allow for unique classification in order for places to be recognizable. In other words, they must encode the bat’s specific locations in space to allow it to recognize previously visited places,” says first author Dieter Vanderelst, PhD, from the University of Antwerp, who led the study as a research fellow at the University of Bristol.
Since it’s impossible to ask a bat about its memory, the researchers built an ‘artificial bat’, a device which contained ultrasonic microphones and an ultrasonic speaker acting as ears and a mouth.
‘Artificial bat’ device. Vanderelst et al., eLife, 2016
Using this device, they collected a large number of echoes from three different locations at heights typical of bat flight (roughly two to three meters). Measurements from each site were gathered and stored by a computer integrated into the device. The team then assessed the templates from the data and found that the echoes returning from each place were unique enough for them to be used to recognize the location.
Using this device, they collected a large number of echoes from three different locations at heights typical of bat flight (roughly two to three meters). Measurements from each site were gathered and stored by a computer integrated into the device. The team then assessed the templates from the data and found that the echoes returning from each place were unique enough for them to be used to recognize the location.
The device in action in a park in Midreshet Ben Gurion, Israel. Vanderelst et al., eLife, 2016
“Importantly, our method used the echoes without inferring the location or identity of objects, such as plants and trees, at each site. In other words, the data support our hypothesis that bats can recognize places by remembering how they sound, rather than how they appear through the animals’ 3D sonar imaging,” Vanderelst explains.
The research also suggests that the use of prominent landmarks might be an emergent feature of template-based place recognition.
“The prominence of a template’s catchment area reflects how likely it is that the template will be observed and stored in a map during exploration. For example, we found the catchment distances to be greater in the Israeli corridor of large boulders than in the corridor of vegetation in the Royal Fort Gardens, suggesting that bats could use the boulders as landmarks for mapping,” Vanderelst adds. “This leads us to believe that cognitive mapping based on templates would show a natural preference to use such landmarks, as they return stronger and more recognizable echo signatures. With these new insights in mind, our aim is to try and piece together the entire puzzle of the navigation tendencies and capabilities in bats.”
Based on material provided by eLife. The paper can be freely accessed online.
“Importantly, our method used the echoes without inferring the location or identity of objects, such as plants and trees, at each site. In other words, the data support our hypothesis that bats can recognize places by remembering how they sound, rather than how they appear through the animals’ 3D sonar imaging,” Vanderelst explains.
The research also suggests that the use of prominent landmarks might be an emergent feature of template-based place recognition.
“The prominence of a template’s catchment area reflects how likely it is that the template will be observed and stored in a map during exploration. For example, we found the catchment distances to be greater in the Israeli corridor of large boulders than in the corridor of vegetation in the Royal Fort Gardens, suggesting that bats could use the boulders as landmarks for mapping,” Vanderelst adds. “This leads us to believe that cognitive mapping based on templates would show a natural preference to use such landmarks, as they return stronger and more recognizable echo signatures. With these new insights in mind, our aim is to try and piece together the entire puzzle of the navigation tendencies and capabilities in bats.”
Based on material provided by eLife. The paper can be freely accessed online.
Dieter Vanderelst Jan Steckel Andre Boen Herbert Peremans Marc W Holderied
University of Bristol, United Kingdom; University of Antwerp, Belgium
DOI: http://dx.doi.org/10.7554/eLife.14188
Published August 2, 2016
Cite as eLife 2016;5:e14188
Abstract
Echolocating bats have excellent spatial memory and are able to navigate to salient locations using bio-sonar. Navigating and route-following require animals to recognize places. Currently, it is mostly unknown how bats recognize places using echolocation. In this paper, we propose template based place recognition might underlie sonar-based navigation in bats. Under this hypothesis, bats recognize places by remembering their echo signature - rather than their 3D layout. Using a large body of ensonification data collected in three different habitats, we test the viability of this hypothesis assessing two critical properties of the proposed echo signatures: (1) they can be uniquely classified and (2) they vary continuously across space. Based on the results presented, we conclude that the proposed echo signatures satisfy both criteria. We discuss how these two properties of the echo signatures can support navigation and building a cognitive map.
DOI: http://dx.doi.org/10.7554/eLife.14188
Published August 2, 2016
Cite as eLife 2016;5:e14188
Abstract
Echolocating bats have excellent spatial memory and are able to navigate to salient locations using bio-sonar. Navigating and route-following require animals to recognize places. Currently, it is mostly unknown how bats recognize places using echolocation. In this paper, we propose template based place recognition might underlie sonar-based navigation in bats. Under this hypothesis, bats recognize places by remembering their echo signature - rather than their 3D layout. Using a large body of ensonification data collected in three different habitats, we test the viability of this hypothesis assessing two critical properties of the proposed echo signatures: (1) they can be uniquely classified and (2) they vary continuously across space. Based on the results presented, we conclude that the proposed echo signatures satisfy both criteria. We discuss how these two properties of the echo signatures can support navigation and building a cognitive map.
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