Frequency of touch, taste, and scent So I was thinking about sound - and how anything below 20Hz is basically inaudible to humans (because it is too low of a frequency to be recognized), as well as anything above around 20KHz (because it is too high of a frequency to be recognized). I was thinking about this in terms of sight (light particles/waves), and how our eyes and ears are basically just frequency detectors for their specific senses. Does the sense of touch have anything to do with vibration on a molecular level? I was wondering if frequency has anything to do with detecting taste, or smelling as well? Do certain foods taste the way they do because of some sort of frequency detection? Do certain scents smell the way they do because of some sort of frequency detection?
 A: Taste and smell are mediated by receptors in your body that molecules can attach to. These receptors then give off an electrical signal which is translated in the brain to a certain taste or smell. The details of this are biological and not of importance here. So no, there is no relevant frequency or even wave-like behavior.
Touch is a very different thing. I am actually not quite sure what causes the sensation we feel when touching something. Partially, there is the rate of heat transfer, which determines how hot or cold an object feels to the touch. Furthermore, the most important physics of touching matter should come from the electromagnetic interaction, but I'm not sure how to translate this to a sensation in our brain. Anyone with more insights should feel free to edit this section of the answer.
A: Taste:
There are 5 basic tastes that the human tongue can detect. They are sweet, savory, salty, sour and bitter. These are detected by taste receptor cells on our tongue, I won't go deep into the biology part.
The basic tastes of sweet, salty and sour have different thresholds, or concentration levels, at which they can be detected. In other words, it is easier to detect some flavors at low concentrations compared with other flavors. Taste thresholds can vary from person to person. So just like sight, our sense of taste also has some thresholds or limitations.
Smell:
It is very similar to taste in the sense that there is an odor detecting threshold for every person which is the lowest concentration of a certain odor compound that is perceivable by the human sense of smell.
Again, the detection is done by receptors in our nose which can detect only certain compounds (odor compounds) to give us the perception of smelling something.
Touch:
The somatosensory system is a complex sensory system. It is made up of a number of different receptors, including thermoreceptors, photoreceptors, mechanoreceptors and chemoreceptors.
This means that when you touch something, you don't just detect one thing. You detect the heat transfer, rigidity, shape etc. When you say something feels cold, it just means it is transferring heat to your body very quickly (like metal). There is also a minimum threshold of vibrations that your touch can detect.
The sense of touch also includes receptors that feel pain (unlike all the other senses) which basically work the same way as the other receptors, except one major difference. The receptors detect something and send electromagnetic pulses to the brain at the speed of light which then sends an appropriate signal as a course of action or conclusion. But when you touch a hot plate, your body needs to tell you that you immediately need to stop touching it because of the huge amount of heat being transferred to your body. So, instead of the brain, the pulse goes to the spinal chord which already has the appropriate course of action 'coded' into it, if you will, and that pulls your hand back immediately. It is involuntary, unlike the others.
