Researchers at Queen Mary University of London and University College London have shown that humans can detect buried objects in sand before touching them, demonstrating what the team describes as a form of remote touch - a capability previously associated with shorebirds such as sandpipers.
Detecting objects in sand is challenging: visual cues disappear, and granular forces behave unpredictably due to shear, jamming, and uneven force propagation.
Animals rely on specialized structures; for instance, shorebirds sense prey through pressure cues transmitted through sediment. Human sensing in opaque, particulate materials, however, has been less understood.
Robotic systems face similar obstacles. Vision and sonar struggle in occluded environments, prompting growing interest in tactile sensing.
Despite progress in modeling granular interactions and developing tactile-equipped robots, the field lacks detailed insight into how humans interpret subsurface cues.
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Investigating Subsurface Object Recognition
To address this, the research team conducted parallel human and robotic experiments. Twelve participants (ages 18-26) used a single fingertip to gently rake through sand while attempting to detect a hidden 5 cm cube. Movements were paced to 2 cm/s with an LED guide to ensure consistent probing conditions.
The robotic setup mirrored this environment. A UR5 robotic arm equipped with a custom four-taxel force sensor and a 7.8 cm “tactile finger” collected real-time force data as it followed predefined trajectories. An LSTM model processed the measurements to classify object presence.
Both studies were grounded in a theoretical prediction that tactile cues in granular media should be detectable up to approximately 7 cm, based on particle interaction and mechanical “reflections” around buried objects.
Key Findings
Human participants detected objects with 70.7 % precision at an average distance of 6.9 cm (median 2.7 cm). Modeling showed that the subtle sand displacements they sensed approach the theoretical physical limits of detectability.
The robot achieved a comparable sensing range, detecting objects at 7.1 cm with a median of 6 cm, but with lower precision (40 %) due to a higher rate of false positives.
These results provide quantitative evidence that humans can perceive buried objects earlier than expected, echoing the remote-touch-like mechanisms seen in certain animals.
The team also found that the two investigations informed each other: human strategies guided the robot’s learning approach, while the robot’s performance offered additional context for interpreting human sensitivity.
Implications
The findings offer benchmarks for developing tactile sensing in robotics and assistive technologies.
Systems modeled on human perception may better support tasks where vision fails, such as probing granular terrain, conducting archaeological investigations, or performing search-and-rescue operations in obscured environments.
Journal Reference
Chen, Z., Crucianelli, L., Versace, E., Jamone, L. (2025). Exploring Tactile Perception for Object Localization in Granular Media: A Human and Robotic Study. 2025 IEEE International Conference on Development and Learning (ICDL), 1-6. DOI: 10.1109/ICDL63968.2025.11204359
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