Photo: Flickr/martinak15At first glance, this may seem like a completely moronic question. I mean, wet stuff feels wet because... well, it's wet. Duh! But when you stop to think more deeply about it it, it quickly becomes a very profound question. That's because, unlike heat or touch, we don't have any sensors in our skin capable of directly detecting wetness. Therefore, scientists believe that we rely on other senses, like temperature or touch, to indirectly sense when something is wet. To test this idea, scientists wet subjects' forearms while interfering with their senses of touch and temperature. Without being able to see their arms, the participants rated how wet they thought they were. In the end, interfering with their senses of touch and temperature did reduce the participants' ability to sense wetness, providing support for the hypothesis. Taking a bath will never feel quite the same again...
Why wet feels wet? A neurophysiological model of human cutaneous wetness sensitivity.
"Although the ability to sense skin wetness and humidity is critical for behavioral and autonomic adaptations, humans are not provided with specific skin receptors for sensing wetness. It has been proposed that we "learn" to perceive the wetness experienced when the skin is in contact with a wet surface or when sweat is produced through a multisensory integration of thermal and tactile inputs generated by the interaction between skin and moisture. However, the individual roles of thermal and tactile cues and how these are integrated peripherally and centrally by our nervous system is still poorly understood. Here we tested the hypothesis that the central integration of coldness and mechanosensation, as subserved by peripheral A-nerve afferents, might be the primary neural process underpinning human wetness sensitivity. During a quantitative sensory test, we found that individuals perceived warm-wet and neutral-wet stimuli as significantly less wet than cold-wet stimuli, although these were characterized by the same moisture content. Also, when cutaneous cold and tactile sensitivity was diminished by a selective reduction in the activity of A-nerve afferents, wetness perception was significantly reduced. Based on a concept of perceptual learning and Bayesian perceptual inference, we developed the first neurophysiological model of cutaneous wetness sensitivity centered on the multisensory integration of cold-sensitive and mechanosensitive skin afferents. Our results provide evidence for the existence of a specific information processing model that underpins the neural representation of a typical wet stimulus. These findings contribute to explaining how humans sense warm, neutral, and cold skin wetness." Related content: NCBI ROFL: Impact of wet underwear on thermoregulatory responses and thermal comfort in the cold. NCBI ROFL: Speedos: not just for streamlining your junk. NCBI ROFL: Apparently, swimming with your clothes on is hard.
