Sensation and Perception


Sensation and Perception

What is Sensation?

 A “sensation” occurs when something around you changes…So what does that mean?

Any aspect of or change in the environment to which an organism responds is called a stimulus.

Example: a light switch being turned on fills a room with light.

What is Sensation?

A stimulus can be measured in a variety of ways including it’s size, duration, intensity, or wavelength.

A Sensation occurs anytime a stimulus activates one of your receptors.

The sense organs then detect any change in energy, such as light, heat, sound, and physical pressure.

What is a Perception?

A sensation may be combined with other sensations and your past experience to yield a perception.

A perception is the organization of sensory information into meaningful experiences.

What are the relationships between sensation and perception?


Psychophysics: The study of the relationships between sensory experiences and the physical stimuli that cause them!

Ok, so that explains how sensation and perception are related…but how are they different?

Fraser’s Spiral

 Fraser’s spiral illustrates the difference between sensation and perception. Our perception of this figure is that of a spiral, but it is actually an illusion.

If you want, trace a circle carefully…You will always come back to the beginning!

Absolute Threshold

In order to determine how we judge sensation and perception, we must first figure out the weakest amount of a stimuli that is required to produce a sensation . In other words, we must find the absolute threshold.

The Absolute Threshold is: the level of stimulus that produces a positive response of detection 50% of the time!

The Absolute Thresholds for the “5” senses in humans are the following:

1. Vision: Seeing a candle flame 30 miles away on a clear night.

2. Hearing: Hearing a watch ticking 20 feet away.

3. Taste: Tasting 1 teaspoon of sugar dissolved into 2 gallons of water.

4. Smell: Smelling one drop of perfume in a 3 room house.

5. Touch: Feeling a bee’s wing falling a distance of one centimeter onto your cheek.

Sensory Adaptation

Psychologists have found that your senses are the most responsive to increases and decreases, and to new events rather than to ongoing, unchanging stimulation.

We are able to respond to the changes in our environment because our senses have the ability to adapt, or adjust themselves, to a constant level of stimulation.

Once your senses get used to a new level of a stimulation, they respond only to deviations from it!

Examples of Adaptation


Your eyes eventually adjust to a darkened movie theatre. At first you see blackness, but eventually, you can see what is going on around you.


When you first jump into a pool that

“feels cold” your body reacts to the stimulus. Eventually, your body adapts to the sensation and you become



When you first walk into a sports locker room, the smell is almost nausiating. After a while, your senses adjust and you can hardly tell.

What do you see…Or don’t you?

The Stroop Effect

Try to name the colors as fast as you can. Not that hard right? How fast are you?

The Stroop Effect

-Now, try to name the colors of the words you see here as fast as you can!

-Not so easy is it?

-How you like them apples?

-Why was it more difficult to name these colors?

A story of a man and a woman…

Then they had a baby

Here is a picture of the baby


How do you perceive yourself? Those around you?

Cars on the road? Noises?


We do not merely have sensory experiences, we perceive objects! The brain recieves information from the senses and organizes and interprets it into meaningful experiences – unconsciously!

This process is called perception !

William Blake

"If the doors of perception were cleansed every thing would appear to man as it is, infinite. For man has closed himself up, till he sees all things through narrow chinks of his cavern."

What would happen if you were able to see for the first time at age 18?

What happens when our senses conflict?

Check out the McGurk Effect

This illustrates what we call

Top-Down Processing

-using our history and knowledge to make meaning out of our reality.


Through the process of perception, the brain is always trying to comprehend the confusion of stimuli that bombard the senses.

The brain makes sense of the world by creating whole structures out of bits and pieces of information in the environment!

This process is called Gestalt !

Gestalt: The experience that comes from organizing bits and pieces of information into meaningful wholes.

Pop Quiz

What is Gestalt?

What are the 4 ways we tend to group things we see?

We organize what we see based on 4 groupings

What do you see?

We group things based on similarity

Now what do you see?

We also group based on proximity

What do you see here?

This is the principle of closure

Which Gestalt principle is being used here?

We also try to make sense out of what we see by using Figure-Ground


The division of experience into figure and ground.

Figure-ground perception is the ability to discriminate properly between a figure and its background.

It is easy to distinguish between 3 dimensional objects, but what about 2 dimensional ones?

Let’s try this one!

Try this test

Selective Attention

When you focus conscious awareness on a particular stimulus to the exclusion of others

 “Cocktail party” effect

Watch this experiment

What does selective attention say about our overall consciousness?

Subliminal Messages

Subliminal messages are brief auditory or visual messages that are presented below the absolute threshold.

 They are presented below the “absolute threshold” so that there is less than a 50 percent chance they that they will be perceived.

Subliminal messages are not as common as you might think.

In fact, the vast majority of what you have probably heard is not true.


Check this out…

Perceptual Set

Perceptual set is a bias or readiness to

Half the class close your eyes and the

Depth Perception

 In order to create a sense of “depth perception,” people use many monocular depth cues to perceive distance and depth.

Monocular depth cues are cues that can be used with a single eye.

One of these very important cues is called motion parallax.

Motion Parallax: the apparent movement of stationary objects relative to one another that occurs when the observed changes position!

Motion Parallax Video

Cues for Monocular Perception

Relative Size

Relative Motion (motion Parallax)


Relative Height

Texture Gradient

Relative Clarity

A Little bit of Depth Perception



What are illusions?

Illusions: perceptions that misrepresent physical stimuli.

Illusions can be very useful in teaching us how our sensation and perceptual rules work.

Illusions are created when our perceptual keys such as size, space, and depth cues are changed!

A very Strange Room!

Extrasensory Perception!

Extrasensory Perception or “ESP”:

An ability to gain information by some means other than the ordinary senses.

There are 4 different types of “ESP”:

1. Clairvoyance – is perceiving objects or information without sensory input.

2. Telepathy – involves the reading of someone else’s mind or transferring one’s own thoughts.

3. Psychokinesis – involves moving objects through a purely mental effort.

4. Precognition – is the ability to foretell future events.

Try this ESP test!

ESP is a very highly contested topic! Why is this?


Synesthesia is a condition in which one sense (for example, hearing) is simultaneously perceived as if by one or more additional senses such as sight.

Get out a sheet of paper and write down the first color that comes to your mind after each number I say….

Check this out !