Is the sixth sense real? Human touch is amazing at detecting cubes under the sand.

Is the sixth sense real? Human touch is amazing at detecting cubes under the sand.

"Touch only works at the 'moment of contact'"—this is what we have long believed. The roughness, temperature, and hardness felt with our fingertips are sensations that arise only when the skin comes into contact with an object. However, recent research quietly shaking this premise has become a topic of discussion. The keyword is remote touch. In other words, it's a perception akin to "touching without contact."


Fingertips detect an "invisible cube" beneath the sand

The stage is set in the sand. Participants gently stroke or lightly move their fingers over the surface of the sand, estimating the position of a small cube buried a few centimeters below. The key point is to provide an answer "before directly touching the object." It's a game of detecting the presence of something through the "cushion" of sand.


The results were astonishing. Despite being a small-scale experiment, participants were able to accurately predict the location of the hidden object with a significant success rate. On average, with a distance condition of about 7 cm, the accuracy reached around 70%. If the conventional wisdom of touch is that "contact equals start," this suggests that the starting line has been moved forward.


Why can we "know without touching"? Tiny signals created by the sand

The mechanism can be imagined as follows. When a finger moves, the sand grains flow slightly, creating localized pressure waves and minute "pushbacks." If a hard object is buried there, the movement of the sand is slightly distorted. Just as a rock beneath the water changes the flow, an area where the sand cannot move "as usual" is created.


This distortion returns to the fingertips as a very small force pattern. The skin receptors pick it up, and the brain estimates, "This movement resembles the response when there is something hard here." The important point is that we use not only "static touch" but also "dynamic touch" in our daily lives. The act of touching is not passive but an active exploration. Remote touch may be an extreme refinement of this active exploration.


Humans vs. Robots: Equal distance, but a difference in "false detections"

What makes this research interesting is that the same task was also given to robots. Equipped with tactile sensors and trained with a time-series data model (LSTM) to learn "sand reaction patterns," the robots could detect to a similar range as humans in terms of average distance. However, they reported more false detections (judging something is there when it isn't), resulting in lower accuracy compared to humans.


Here, the "human-like" quality of touch emerges. Human fingertips not only have high-performance sensors but also adjust their movements according to the situation. If too fast, the noise from the sand increases. If too slow, no clues emerge. By changing slight angles, pressure, and speed, the brain runs predictions like "What should happen if I move like this next?" and signals that deviate from predictions emerge as "signs of foreign objects." The struggle of robots may be due to the difference in comprehensive ability between prediction and adaptation rather than sensor performance.


Practical applications: Excavation, rescue, space, and medicine

Where could remote touch be practically applied? The most imaginable is in excavation and archaeology. If it is possible to detect "there is something hard beneath" before unearthing fragile artifacts, the way tools are used can be altered. Next, exploration in poor visibility situations. The potential to detect hazardous objects or voids hidden in rubble, gravel, or powder early through touch exists.


Furthermore, in areas with sandy or granular surfaces—such as planetary exploration. If it becomes possible to estimate hard layers or obstacles beneath the surface from its behavior, decision-making regarding traversability becomes smarter. In the medical field, there might be hints for designing tactile feedback (remote operation, assistance in minimally invasive surgery). The technology to "obtain information as if touched in situations where direct contact is not possible" is one of the key areas in remote medical care and robot-assisted surgery.


Reactions on social media: Romanticists vs. realists, debates usually split into two

When such topics arise, social media and comment sections generally split into two camps. In comments on articles from overseas media, realists first say, "Isn't that just an extension of normal touch, not a sixth or seventh sense?" "If it's just feeling changes in density, calling it a 'new sense' is an exaggeration." Those strict about the definition of senses tend to point out "classification issues." There are also calm retorts like, "It's like not calling the ability of vision to estimate depth a 'new sense.'"


On the other hand, romanticists enjoy the impact of the words. Comments link it to "memories of experiences," such as "The human body still has hidden functions," "Would accuracy improve with training?" and "Is this why I was good at finding shells on the beach as a child?"


Meanwhile, practicalists expand their imagination towards applications, saying, "It seems beneficial for robotics," and "Could it transform fields like disaster rescue or landmine detection?" Since the research itself compares humans and robots, the flow of "making machines smarter by taking hints from human strategies" seems the most realistic.


Caution about the term "seventh sense": It's a new discovery, not a superpower

The important point here is that remote touch is not proof of "superpowers." There is a medium of sand, an input of moving fingers, and as a result, a pattern of minute forces is returned. There is a physical causality. What's interesting is rather that "our bodies can read those minute patterns more than expected." It's less misleading to see it as an extension of the "reach of touch" by combining existing tactile sense and motor control, rather than the addition of a new sensory organ.


However, avoiding misunderstandings does not diminish the value of the discovery. Human senses are not independent boxes but systems intertwined with movement, prediction, attention, and learning. Remote touch is valuable in visualizing the unexpected strengths of this system in a sandy environment.


Next focus: Can anyone do it? How much can it be trained? Does it occur beyond sand?

The future points of discussion are simple.


The first is individual differences. Performance should vary with finger moisture, skin condition, experience, and focus of attention.


The second is material differences. Changes in sand grain size, humidity, and temperature will alter the "signals returned." How generalizable is the phenomenon across gravel, powder, soil, and snow?


The third is the learning effect. If accuracy improves with training, it could lead to the design of tactile training.
And the fourth is engineering applications. Can we extract human exploration movements (what speed, pressure, and trajectory are advantageous) and apply them to robot control? This seems to be the area with the most potential for growth.


Touch, though inconspicuous, supports our understanding of the world. The glass of a smartphone, the fibers of clothing, the resistance of a keyboard—most of our daily life is made up of "tactile clues." The story of remote touch, where this tactile sense behaves as if it slightly crosses the boundary of the skin, reminds us of the depth of our bodies. The range within which we feel the world might be wider than we think.


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