The Five Senses

Our senses allow us to experience the world we live in, and are one of the key components of consciousness. In fact our senses are so important that whole industries have been built upon a single sense.

For example, radio is associated with hearing, cooking with taste, fragrance with smell and television with both vision and hearing.

As you can see without our senses the world would be a very different place, as we would not be able to experience all the various things it has to offer.
 
If we were not able to experience things then learning would also become impossible, since in order for us to learn something we must first be capable of experiencing it.

This is why the study of our senses, or sensation, is considered to be such an important area of psychology, because it is one of the key components that makes consciousness possible.

Below you will find a description of our senses.

Vision

Most people consider vision to be their primary sense, as virtually everything we do involves the use of vision.

However in order to understand vision, we first need to look at the stimulus that make it possible: light.

What Is Light?

Light consists of a set of electromagnetic waves, which travel at a speed of around 186,000 miles per second.

Electromagnetic waves, as the name suggests, are made up of electrical and magnetic fields that possess the ability to travel through a vacuum.

Note : A vacuum is a space completely devoid of matter, and contains no air or gas.

This is why it is possible for Earth to communicate with astronauts in space, as radio waves are one kind of electromagnetic wave.

The waves we call light, exist within a relatively narrow band of the electromagnetic spectrum. This spectrum ranges from long radio waves at one end, to short gamma rays at the other end.

Light waves are found in between these two extremes, and are said to have a length of 750-400 nanometres.

The part of the electromagnetic spectrum that we can see is called the visible spectrum, and starting at 750 nanometres, consists of the colours red, orange, yellow, green, blue, indigo and violet.

These are the same colours that appear in a rainbow, and are always found in the same order.

Waves that are longer than 750 nanometres are called infra-red rays, and waves which are shorter than 400 nanometres are called ultra-violet rays. Both of which we cannot see.

The Eye

Although light is necessary for vision, in order for us to see something we need to be able to convert that light into useable information. This is done through our sensory organ, the eye.

In front of the eye is the cornea, which due to its convex shape bends light waves and makes them converge on the lens.

The lens then focuses these light waves, and produces an inverted (upside down) image on the retina. The retina contains a series of light sensitive neuronscalled photoreceptor’s.

In the centre of the retina is the fovea, which determines how well we can see something (visual acuity) and the colour of what we see (colour vision).

The outer periphery of the retina plays a role in detecting light signals and the brightness of what we see.

There are two kinds of photoreceptor’s in the retina. The first are called cones which are mainly found in the fovea, and the second are called rods which are mainly found along the outer periphery.

The Trichromatic Theory Of Colour Vision

One of the leading theories of how we see things in colour (colour vision) is the Trichromatic theory.

This theory hypothesises that we have three kinds of cones in the eye that are differentially sensitive to three wavelengths of light: 750 nanometres, 500 nanometres and 450 nanometres.

In turn, each of these wavelengths gives us the sensation of a colour.

The first wavelength of 750 nanometres creates the sensation of red, the second wavelength of 500 nanometres creates green, and the third wavelength of 450 nanometres creates blue.

It is important to note that this theory does not suggest that colour comes from light, but rather that colour is produced as a result of the firing of photoreceptor’s.

To account for the sensation of colours others than red, green and blue, the Trichromatic theory proposes that certain wavelengths of light cause the simultaneous firing of multiple neurons.

For example, the sensation of orange occurs because a wavelength of 650 nanometers causes the firing of some neurons which normally fire at 750 nanometres and some neurons which normally fire at 500 nanometres.

In other words, other colours are created by activating multiple cones so that their colours are mixed to create another colour, similar in principle to how colours are mixed in a paint set.

White light, the theory proposes, is created as a result of all the wavelengths arriving at the retina in a random or scrambled fashion which causes all three cones to fire at once.

Whilst the Trichromatic theory is a widely accepted view of how colour vision works, it is not perfect.

For example, according to the theory people who are red-green blind (colour blind) would not be able to see yellow, yet they are able to do so.

So whilst the Trichromatic theory may explain at a lot about how we see in colour, it does not explain everything.

Sensations Of Vision

There are three basic sensations of vision as proposed by Wilhelm Wundt.

Hue

The ability to distinguish colours from each other. To see a range of colour.

Brightness

The level of illumination we see in a colour, such as white vs. black.

Saturation

How rich a colour appears to be.

Hearing

Hearing is another important sense that allows us to experience the world, as without it we would live in social isolation.

A good example of this occurs when talking to another person. If we were not able to hear what they were saying, our communication with them would be extremely limited.

As a result, people who are unable to hear sound (because they are deaf) learn sign language so that they can overcome this isolation caused by their inability to hear sound.

Just like vision, the sense of hearing can be better understood by studying the stimulus that makes hearing possible, the sound wave.

Sound Waves

Sound waves are created from a vibrating source, and require a medium such as air or water to travel in.

For example, by plucking a guitar string we cause a wave of vibrations to spread through the air, which eventually strike our ear drum enabling us to hear it as a sound.

The rate of this vibration is called the frequency, and is measured in hertz (Hz). One hertz is equal to one vibration (or cycle) per second, and the more something vibrates (the more cycles per second / the higher the hertz) the higher the pitch we hear will be.

The intensity of a sound wave is measured in decibels (dB), whereby the greater the decibel level is the louder the sound will be.

The Ear

The ear allows us to experience the sensation of sound. When sound reaches the eardrum (aka the tympanic membrane) it causes it to vibrate. These vibrations are then passed onto a structure known as the oval window.

This is made possible by three bones called the Malleus (hammer), the Incus (anvil) and the Stapes (stirrup).

The vibrations in the oval window are passed onto the cochlea, which is a fluid filled spiral structure that looks similar to a snail shell.

Inside the cochlea is the basilar membrane, which plays a similar role in hearing as the retina does in vision. Ultimately sound is passed onto the brain via the auditory nerve.

Sensations Associated With Hearing

There are three main sensations associated with hearing:

Pitch

The ability to hear low to high pitched sounds.

Loudness

How loud a sound is.

Timbre

How rich a sound is. The quality of that sound. Similar to the saturation of colour.

Taste

Taste is made possible by clusters of neurons on the tongue known as taste buds, which are stimulated by various chemical compounds found in food and liquids.

In response to these compounds the taste buds produce four basic taste sensations; sweet, salty, bitter and sour.

All four of these taste sensations combine in different combinations to give us the many flavours we experience in foods and drinks.

The taste buds are grouped together in specific areas on the tongue. For example, taste buds for sweetness are found near the tip of the tongue.

However what we taste does not come purely as a result of the chemical compounds found within a food, as taste interacts with other senses which then affects how something tastes to us.

For example, when you cook dinner taste can be affected by how the meal is presented, the type of smell it has and also how that food feels once we put it in our mouth.

Touch

Touch is more accurately defined in terms of skin sense, of which there are four different kinds.

Light Touch

The first sense is light touch, which we sense when slight or gentle pressure is applied to the skin. For example, lightly stroking the skin.

Deep Touch

The next sense is deep touch, which we feel when heavy pressure is applied to the skin. For example, a firm handshake.

Temperature

The receptor neurons in our skin can detect changes in temperature. When heat is conducted towards the skin, we feel a localised heat or warmth in that area. For example, putting your hand over a flame.

When heat is conducted away from the skin, we feel cold. For example, walking bare feet on the floor.

Pain

When our skin becomes damaged (such as when it is cut) the neurons in our skin detect this damage and we register it as pain.

Smell

The sense of smell is known as olfaction, and allows us to detect chemical substances in the air via the olfactory epithelium in the nose.

Although there is no firmly established number of smell sensations, there are four that are agreed upon.

Putrid

This is the smell of something rotting or decomposing

Floral

The smell of flowers.

Pungent

The smell of burning food.

Spicy

Like the smell of cinnamon.

Kinaesthesia

The kinaesthetic sense is the ability to known the position of your body, even when your eyes are closed.

For example, providing your kinaesthetic sense is working correctly, if you close your eyes you should be able to touch the tip of your nose.

This sense therefore allows you to move your body without having to remember where each body part is, such as when you are walking or running.

The receptor neurons which make the kinaesthetic sense possible, are found in the connective tissue surrounding the bodies joints and also within the joints themselves.

Sense Of Balance

The sense of balance tells you whether you are in an upright position or not.

The way the body detects this is by fluid in the semicircular canals in the ears. The movement of the fluid stimulates the firing of receptor neurons, which tells the brain what sort of position you are in.

This sense is also known as the vestibular sense.

Summary

• Sensation is also referred to as the raw data of experience.

• Our five senses allow us to experience our external environment.

• Light is an electromagnetic wave that is able to travel through a vacuum.

• The visible part of the electromagnetic spectrum ranges from 750 nanometres to 400 nanometres, and consists of the colours red, orange, yellow, green, blue, indigo and violet.

• Photoreceptors in the retina called cones and rods allow us to see light. The optic nerve then passes what we see onto the brain.

• The Trichromatic theory states that we have three different kinds of cones which are differentially sensitive to light, and allow us to see in colour.

• The theory states that we see white light as a result of all wavelengths arriving at the cones in a random fashion, which causes all cones to fire simultaneously.

• Red-Green colour blind people show that the Trichromatic theory is not perfect.

• The three sensations associated with vision are hue, brightness and saturation.

• Sound is created from a vibrating source that creates a sound wave which reaches our eardrum

• Sound requires a medium such as air or water to travel through.

• Sound is measured in hertz, which is a measure of how many times sound vibrates per second. This is known as the frequency of sound.

• Decibels are used to measure the loudness of sound.

• Sound waves which hit the eardrum (aka the tympanic membrane) are passed to the oval window, the cochlea, the basilar membrane and onto the brain via the auditory nerve.

• The basilar membrane is similar in function to the eyes retina.

• The three sensations associated with hearing are; pitch, loudness and timbre.

• Taste buds are clusters of neurons on the tongue which allow us to taste things.

• The four sensations associated with taste are sweet, salty, bitter and sour.

• There are around 10,000 taste buds.

• Taste interacts with other senses such as touch, smell and vision.

• Touch is more accurately defined by referring to it as skin senses.

• There are four skin senses; light touch, deep touch, temperature and pain.

• The sense of smell is known as olfaction, and is made possible by the olfactory epithelium which is located in the nose.

• There are four agreed upon smell sensations; putrid, floral, pungent and spicy.

• The kinaesthetic sense is the ability to know the relative position of various parts of your body.

• The sense of balance is also called the vestibular sense.

• The vestibular sense is made possible by receptor neurons in the fluid filled semicircular canals in the inner ear.