Super Seal Sense: Whisker movement strategies in Pinnipeds

Active touch theory states that sensors must move and engage in task-specific behaviours in order to improve efficiency and performance in sensory tasks. Human fingertips are an active touch system as they make purposeful, task-specific movements, for example they sweep over textures, feel around edges to judge shape and squeeze objects to judge hardness. Most mammals do not have mobile, tactile fingertips and they have whisker touch sensors instead. Whiskers are part of a unique sensory system and are highly sensitive and moveable. Although many researchers assume whiskers do active touch sensing, it has never been quantitatively investigated in any animal.

Seals, Sea lions and Walruses, use their whiskers for foraging, navigation and object identification in dark and murky underwater habitats. They have the longest and most sensitive whiskers of all mammals, that are specially-shaped and are moved systematically with purpose. Seal whiskers are undulating while sea lion and walrus whiskers are smooth. These shape specialisations are likely to affect what the animal can feel with their whiskers. However, no one has ever investigated this.

For this fellowship I will characterise active touch sensing strategies in seals and sea lions using behavioural experiments, 3D mechanical models and robot platforms. I suggest that the control of specially-shaped whiskers allows Seals and Sea lions to discriminate between different objects. I will discover if actively controlling whiskers enables them to sense more efficiently, improving our understanding of active sensing, whisker mechanics and motor control. This will be tested by:

1. Describing whisker movements in Harbor seals (wavy whiskers) and South African fur seals (smooth whiskers). Animals will be trained at SeaQuarium Rhyl to complete 3 different tasks: colour, texture and size while blindfolded and selecting a target object from a range of different distractors. The whiskers will be filmed underwater and tracked allowing me to visualise how whiskers move during each different discrimination task.

2. Identifying task-specific whisker strategies in Harbor seals and South African fur seals using three different discrimination tasks as detailed above.

3. Estimating how whisker shape effects sensation by investigating different forces applied along the whisker using mechanical models and a robot sensor. I expect whisker shape to affect the bend of a whisker when in contact with an object. Dissected seal and sea lion whiskers from museum specimens will be scanned and modelled in specialist 3D software (called Finite Element Analysis) looking at how an object behaves in a given situation.

4. Exploring how different-shaped whiskers (wavy or smooth) affect movement strategies. Dissected Pinniped whiskers will be attached to a robot sensor arranged like a muzzle; the robot will make movements to detect object size and texture. Robot movements will be compared to my experimental data to see how efficient seals and sea lions are at sensing. This will improve our understanding of active sensing and whisker mechanics, by combining aspects of anatomy, whisker tracking, whisker robotics and detailed 3D digital models.

5. Examining if these strategies are altered during a hydrodynamic task (the ability of some animals to sense water movements). My tactile task will be adapted to a hydrodynamic task and whisker and head movement strategies will be compared.

Human fingertips are an active touch system as they make purposeful, task-specific movements. The primary tactile sensor in most mammals are whiskers. While studies have referred to whiskers as an active sense, no one has ever identified task-specific whisker movements in any animal, determined by making different whisker movements during different tasks. As opposed to other sensory systems, whiskers are comparatively large, easy to see and easy to measure, making them an ideal system to test active sensing theories. Pinnipeds have the most prominent and sensitive whiskers of any mammal that are purposefully controlled. However, we do not know if the kinematics of whiskers differ depending on a task. Pinniped whiskers vary in size, length, number and shape. These differences affect the mechanics of whisker signals, received by each whisker follicle. How whisker shape affect follicle forces is unknown, although it is likely that undulating whiskers are more stable when sensing underwater. I suggest active control of specially-shaped whiskers allows Pinnipeds to efficiently discriminate between objects. I will explore this by designing novel training tasks, with state-of-the-art 3D whisker imaging. I will identify active sensing strategies during a texture, size and visual task in Phocids (undulating whiskers) and Otariids (smooth whiskers). I will estimate how whisker shape effects the interaction between whisker and follicle using linear FEA models and a robot whisker sensor with real Pinniped whiskers. I will use the robot sensor to test sensory movement strategies and identify the efficiency of Pinniped sensing, comparing robot sensor movements to those of Pinnipeds. I will also compare tactile and hydrodynamic sensing strategies, by developing a hydrodynamic task. This unique project will reveal how whiskers move as an active sensory system and their functional significance, transforming our understanding of mammalian mechanosensation and motor control.