8.1Contact Forces Lesson 12, how do we sense different textures?

How do we sense different textures?

Discovering the intricacies and wonders of our tactile perception through scientific exploration and sensory experiences.

​When we touch a material, we feel the texture of that material. We can tell if something is hard or soft just by placing our skin on the object. Have you ever considered how we can tell if something is hard or soft? It turns out the answer is deformation due to a contact force!

We learned in Lesson 5 that we can feel objects when the pressure sensors in our skin deform. We also learned these pressure sensors, or force detectors, are all over our body. It is estimated that you have roughly 150,000 of these in each hand! The special sensors for detecting force are called mechanoreceptors. Let’s learn more about how the skin senses different textures and softnesses.

Multiple Choice

What is the role of pressure sensors in our sense of touch?

• Detecting and measuring pressure applied to the skin's surface

• Enhancing our sense of taste

• Regulating body temperature

• Improving our sense of smell

Dropdown

The special pressure sensors that humans have are called ​​

Select answer

Deformation & Contact Force

• Sense of Touch: Vital for perception & interaction

• Deformation: How objects change shape when touched

• Contact Force: Pressure exerted during touch

​When your finger touches a surface, part of your finger deforms. Things that feel sharper deform more of your finger and touch less surface area. Take a finger and touch your desk. Your finger touches the surface and then it starts to deform so that the entire pad of your finger is touching the surface of the desk. Now, take your pencil and use the point of your pencil to touch the pad of your finger. Does it feel different? The reason that the pencil feels sharper is because it makes your finger deform more and less surface area is in contact with the object. The table felt smooth or dull because it did not indent, or deform, your finger as much as the pencil point. The table also pressed on the whole pad of the finger, not just a small area.

​The feeling of sharp vs dull

​This pencil causes a lot of deformation to the pad of the finger, but it touches a very small surface area at the lead point. Because it touches such a small area and there is a large deformation, the brain senses this pencil as sharp.

Dropdown

In the example on the previous page, a pencil caused a lot of deformation. Because it touches a small ​

Select answer

the brain senses it as sharp.

The feeling of smooth vs rough

When you run your hand across different surfaces, some feel smooth and others feel rough. Run your hand across a surface that is rougher, like the stitching on your backpack, a zipper, or the metal part of your pencil. Now run your hand across a surface that is smoother, like the top of your desk or the side of your pencil. Which one had more areas of deformation as you moved your finger across the surface? The rough surface makes many different spots on your finger deform as your finger moves across the surface, and the smooth surface does not have as many spots that cause deformation to the finger on multiple locations. The smooth surface does not deform your finger as much when your finger runs across the surface.

​As the finger runs across this pencil, it does not encounter multiple areas of deformation and the pressure is consistent on the pad of the finger. This causes the brain to sense the pencil side as smooth.

Draw

Create an illustration that visually explains how different textures are detected on the skin. Use arrows and labels to show the process of deformation and the role of mechanoreceptors in sensing texture

Multiple Choice

A rough surface makes many different spots on your finger deform as your finger moves across the surface

• True

• False

The feeling of soft vs hard

When your hand touches something soft, the soft item deforms around your finger. The soft surface is deformed due to the pressure of your finger pushing on it. If your finger deforms the surface instead of the surface deforming your finger, it feels softer. Cotton balls feel soft because of how much they deform when we apply pressure. The surface touches a very large part of our fingertips with very little force being applied. Our bodies know when we are applying pressure, and the more we apply pressure without the resistance, the softer an object feels.

This cotton ball deforms when a contact force from the finger is applied. The finger senses that it is in contact with the cotton ball, and the cotton ball deforms more than the pad of the finger. This causes the brain to sense the cotton ball as soft.

Drag and Drop

The more we apply pressure without the resistance, the ​

Placeholder

an object feels.

Drag these tiles and drop them in the correct blank above

softer

harder

rougher

smoother

How our brains receive the signal

Our sense of soft vs. hard depends on the amount of pressure and deformation on our skin. When the finger is deformed, it sends signals through our nerves to the brain that then interprets the texture of the objects. Our brain turns this signal into information that we can use.

Multiple Choice

What makes a surface feel smooth?

• Multiple areas of deformation

• Consistent pressure on the finger

• Less deformation of the finger

• More spots causing deformation

Multiple Choice

What happens when a soft surface is touched?

• The surface deforms the finger

• The finger deforms the surface

• No deformation occurs

• The finger slides off the surface

Multiple Choice

What determines our sense of soft vs. hard?

• The color of the object

• The temperature of the object

• The amount of pressure and deformation on our skin

• The weight of the object

Multiple Choice

How does our brain receive the signal of texture?

• Through our nerves

• Through our sense of smell

• Through our sense of hearing

• Through our sense of sight