“Whisker specialists” such as rats, shrews, and seals actively employ their whiskers to explore their environments and extract object properties such as size, shape, and texture. It has been suggested that whiskers could be used to discriminate between different sized objects in one of two ways: (i) to use whisker positions, such as angular position, spread or amplitude to approximate size; or (ii) to calculate the number of whiskers that contact an object. This study describes in detail how two adult harbor seals use their whiskers to differentiate between three sizes of disk. The seals judged size very fast, taking <400 ms. In addition, they oriented their smaller, most rostral, ventral whiskers to the disks, so that more whiskers contacted the surface, complying to a maximal contact sensing strategy. Data from this study supports the suggestion that it is the number of whisker contacts that predict disk size, rather than how the whiskers are positioned (angular position), the degree to which they are moved (amplitude) or how spread out they are (angular spread).
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The authors would like to thank Lars Miersch and Dr. Federike Hanke for their help with designing and planning the set-up, also to Dr. Ben Mitchinson for his support with tracking software. Work for this study was funded as part of the BIOTACT FP7 Bio-ICT project, by a Research Stay Grant from the German Academic Exchange Service (DAAD) awarded to R. G., and also by the Volkswagen-Foundation. We thank three anonymous reviewers and Dr Wolf Hanke for helpful comments on the manuscript.
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Grant, R., Wieskotten, S., Wengst, N. et al. Vibrissal touch sensing in the harbor seal (Phoca vitulina): how do seals judge size?. J Comp Physiol A 199, 521–533 (2013) doi:10.1007/s00359-013-0797-7
- Active touch
- Maximal contact