Although it might appear obvious that individuals can feel rain or seawater, yet human bodies cannot truly "detect" the water on their skin. The reality is that bodies lack specific sensors for liquid detection. Instead, humans depend on a combination of other sensors to signal wetness.
Unraveling the Complex Mechanisms of Somatosensory Perception
Humans can feel rain during a storm or seawater when jumping into the ocean, but our bodies don't possess specific sensors for liquid detection. Instead, humans rely on the somatosensory system, a network of neurons, to process touch-related information. These specialized neurons, including mechanoreceptors and thermoreceptors, transmit tactile details from the skin to the brain, enabling us to recognize objects, textures, or temperatures.
Unlike animals like cockroaches or honeybees, humans lack hygroreceptors, which directly detect changes in moisture and humidity. Instead, we depend on a complex interplay of other sensory inputs to infer wetness.
Jonathan Samir Matthis, an assistant professor of human movement neuroscience, explains that humans form a perception of the presence of water based on accumulated evidence.
Humans employ visual stimuli and tactile sensations to identify liquids. For instance, observing water flow and feeling droplets hitting the skin contribute to this process. However, the most significant cue for sensing water through the skin is temperature.
Davide Filingeri, an environmental and sensory physiologist, notes that moisture on the skin tends to evaporate, causing a cooling effect. Humans may have developed an association between the sensation of coolness and the presence of wetness.
This link between coolness and wetness might explain phenomena like the difficulty in determining dryness on a cold day or the sensation of sitting in a puddle on a cold metal chair.
In a 2013 study, Filingeri and his team blindfolded participants and used a dry probe with varying cold temperatures on their forearms. Some participants perceived the dry stimuli as wet, emphasizing that the brain relies on temperature cues to distinguish wetness.
The brain struggles to differentiate between the illusion of wetness and actual wetness, highlighting the intricate nature of human perception in this regard.
Sensing Wetness: Brain Insights in Product Design and Medical Applications
The feeling of wetness is a sensation often overlooked, detected by the brain through cues like temperature and touch. Innovative research is leveraging these insights for practical applications in product design, influencing items ranging from diapers to deodorants.
In 2014, Filingeri conducted an experiment wherein he investigated the impact of warm, wet stimuli on blindfolded participants. The results revealed that individuals were unable to perceive wetness when the simulations surpassed 7.2°F (4°C) above their skin temperature.
Building on these findings, Filingeri is collaborating with clothing designers to develop breathable sportswear specifically crafted to effectively manage perspiration. Concurrently, his lab is partnering with the Swiss Federal Institute of Technology Lausanne (EPFL) to restore thermal sensations in amputees using prosthetics.
This innovative approach allows them to create a simulated sense of wetness in their absent limbs. Filingeri anticipates various clinical and nonclinical applications emerging from this research.
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