Sensation and Perception

Whenever we hear the words ‘psychology’, our mind wandered about magic or mystery.   In many television programs or movies, it often shows that psychologist as reading mind and solving the mystery of the crime.  Also we often sees a scene where a psychologist listening tentatively to a client about their problems.  What is shown on television is indeed how psychology works but there not only solve problems or listening to their client’s problem, they help people with all sorts of problems, working with them to bring about change for the better.

We use psychology every day in our life, in our parenting skills in communicating with our children, to correct our child’s behaviour and helping them in their learning.  We also use psychology in negotiation with a salesperson to give you good discount and we do this with the right communication and facial expression.  From everyday actions and interactions to the rarer triumphs and tragedies of life, psychology is all around us and it helps us in many ways.

What is psychology and why is it so interesting? Psychology is more than magic, illusion or problems.   Psychology is the scientific study of behaviour and mental process in both human and animals by thorough observation.  The study behaviour that includes our outward or overt reactions, such as talking, facial expressions and movement and mental process that refers to all the internal, covert (hidden) activity of our minds, such as thinking, feeling and remembering.

We learned from young about the five senses and how it helps us in our daily life.  We us our eyes to see, ear to listen, nose to smell, touch to feel and tongue to taste.  All of these senses give us information (sensation) which our brains have to interpret (perception).  But there are people who are not born with these five senses, so they use their senses and interpret in different way.  For example a blind people cannot use their eyes to see but they build pictures using his sense of touch, by listening to the echoes of clicks of his tongue and taps of his cane as these sounds bounce off objects in his surroundings, a technique called echolocation.

The words ‘sensation’ and ‘perception’ are interrelated, which makes it quite easy to mix up the definition of the two words. Sensation is essentially the ‘feeling’ what we feel with our senses. Sensations are things in our environment that are registered by the five major sensory organs. Sensation is what we see, hear, smell, taste and feel. Perception is how we interpret these sensations. Perception helps us make sense of our sensations.

This paper will explain more on what sensation and perception all about.  How we interpret the world around us.


Sensation is the process by which our senses gather information and send it to the brain.  A large amount of information is being sensed at any one time such as room temperature, brightness of the lights, someone talking, a distant train, or the smell of perfume.  With all this information coming into our senses, the majority of our world never gets recognized.  We don’t notice radio waves, x-rays, or the microscopic parasites crawling on our skin.  We don’t sense all the odours around us or taste every individual spice in our gourmet dinner.  We only sense those things we are able too since we don’t have the sense of smell like a bloodhound or the sense of sight like a hawk; our thresholds are different from these animals and often even from each other.

5 senses

What is sensation?  Sensation occurs when special receptors in the sense organs – the eyes, ears, nose, skin, and taste buds are activated, allowing various forms of outside stimuli to become neutral signals in the brain.  This process of converting outside stimuli, such as light, into neutral activity is called transduction. (K.Ciccarelli. N. White. Pearson. Pg. 128)

The sensory receptors are specialized forms of neurons, the cells that make up the nervous system.  Instead of receiving neurotransmitters from other cells, these receptor cells are stimulated by different kinds of energy- for example, the receptors in the eyes are stimulated by light, whereas the receptors in the ears are activated by vibrations.  Touch receptors are stimulated by pressure or temperature, and the receptors for taste and smell are triggered by chemical substances.  Each receptor type transduces the physical information into electrical information in different ways, which then either depolarizes or hyperpolarized the cell, causing it to fire more or to fire less based on the timing and intensity of information it is detecting from the environment (Gardner & Johnson, 2013).


Ernst Weber (pronouned vay-ber), a 19th century experimental psychologist, observed that the size of the difference threshold appeared to be lawfully related to initial stimulus magnitude.


Figure 2 – Ernst Weber(1975-1878)

Weber’s Law, more simply stated, says that the size of the just noticeable difference (i.e., delta I) is a constant proportion of the original stimulus value.  For example: Suppose that you presented two spots of light each with an intensity of 100 units to an observer.  Then you asked the observer to increase the intensity of one of the spots until it was just noticeably brighter than the other.  If the brightness needed to yield the just noticeable difference was 110 then the observer’s difference threshold would be 10 units (i.e., delta I =110 – 100 = 10).  (WebersLaw.html). His research led the formulation known as Weber’s law of just noticeable differences (jnd, of the difference threshold).

Gustav Fechner (1801-1887) expanded on Weber’s work by studying something he called the absolute threshold (Fechner,1860).  An absolute threshold is the lowest level of stimulation that a person can consciously detect 50 percent of the time the stimulation is present.  For example, assuming a very quiet room and normal hearing, how far away can someone sit and you might still hear the tick of their analog watch on half of the trials?  Figure 1 is the examples of absolute thresholds for various senses.


Sense Detection Threshold
Vision A candle flame at 30 miles on a dark, clear night
Hearing The tick of a mechanical watch under quiet conditions at 20 feet
Taste One teaspoon of sugar in 2 gallons of water
Smell One drop of perfume diffused into the entire volume of a three-bedroom apartment
Touch The wing of a bee falling on your cheek from a distance of 1 centimeter

Stimuli that are below the level of conscious awareness are called subliminal stimuli. (the word limin means “threshold, “so sublimin means “below the threshold.)  These stimuli are just strong enough to activate the sensory receptors but not strong enough for people to be consciously aware of them.  Many people believe that these stimuli act upon the unconscious mind, influencing behaviour in a process called subliminal perception.


Some of the lower centers of the brain filter sensory stimulation and “ignore” or prevent conscious attention to stimuli that do not change.  The brain is primarily interested in changes in information.  That’s why people don’t change.   That’s why people don’t really “hear” the noise of the air conditioner unless it suddenly cuts off, or the noise made in some classrooms, unless it gets very quiet or someone else directs their attention toward it.  Although they actually are hearing it, they aren’t paying attention to it.  This is called habituation and it is the way the brain deals with unchanging information from the environment.   For example, you don’t like to eat ‘tuhau’ ( a Sabah local traditional food) when you eat, the food you put in your mouth tastes strong at first, but as you keep eating the same thing, the taste does fade and you beginning to get used to it.  All our senses are subject to sensory adaptation.


When we are in a crown room with lots of people talking, we find it difficult to focus on any particular stimulus, like the conversation we are having with a friend.  We try to focus our attention and at the same time trying to ignore the flood of information entering our senses.  When we do this, we are making a determination as to what is important to sense and what is background noise.  This concept is referred to as signal detection because we attempt detect what we want to focus on and ignore and minimize everything else.


What is Perception?  Perception is the method by which the brain takes all the sensations a person experiences at any given moment and allows them to be interpreted in some meaningful fashion.  Perception has some individuality to it.  For example, two people might be looking at a cloud and while one thing it’s shaped like a horse, the other things it’s more like a cow.  They both see the same cloud, but they perceive that cloud differently.  As individual as perception might be, some similarities exist in how people perceive the world around them. (K. Ciccarelli. N. White. Pearson. Pg. 154)


Imagine if every time an object changed we had to completely reprocess it.  The next time you walk toward a building, you would have to re-evaluate the size of the building with each step, because we all know as we get closer, everything gets bigger.  The building which once stood only several inches is now somehow more than 50 feet tall.

Luckily, this doesn’t happen.  Due to our ability to maintain constancy in our perceptions, we see that building as the same height no matter what distance it is.  Perceptual constancy refers to our ability to see things differently without having to reinterpret the object’s properties.  There are typically three constancies discussed, including size, shape, brightness.

Size constancy refers to our ability to see objects as maintaining the same size even when our distance from them makes things appear larger or smaller.  This holds true for all of our senses.  As we walk away from our radio, the song appears to get softer.  We understand, and perceive it as being just as loud as before.  The difference being our distance from what we are sensing.

Everybody has seen a plate shaped in the form of a circle.  When we see that same plate from an angle, however, it looks more like an ellipse.  Shape constancy allows us to perceive that plate as still being a circle even though the angle from which we view it appears to distort the shape.  Brightness constancy refers to our ability to recognize that colour remains the same regardless of how it looks under different levels of light.  That deep blue shirt you wore to the beach suddenly looks black when you walk indoors.  Without colour constancy, we would be constantly re-interpreting colour and would be amazed at the miraculous conversion our clothes undertake.


The German word “Gestalt” roughly translates to “whole” or “form,” and the Gestalt psychologist’s sincerely believed that the whole is greater than the sum of its parts.  In order to interpret what we receive through our senses, they theorized that we attempt to organize this information into certain groups.  This allows us to interpret the information completely without unneeded repetition.  For example, when you see one dot, you perceive it as such, but when you see five dots together, you group them together by saying a “row of dots.”  Without this tendency to group our perceptions, that same row would be seen as “dot, dot, dot, dot, dot,” taking both longer to process and reducing our perceptive ability.  The Gestalt principles of grouping include four types: similarity, proximity, continuity, and closure.



Similarity refers to our tendency to group things together based upon how similar to each other they are.  In the first figure above, we tend to see two rows of red dots and two rows of black dots.  The dots are grouped according to similar colour.  In the next figure, we tend to perceive three columns of two lines each rather than six different lines.  The lines are grouped together because of how close they are to each other, or their proximity to one another.  Continuity refers to our tendency to see patterns and therefore perceive things as belonging together if they form some type of continuous pattern.  In the third figure, although merely a series of dots, it begins to look like an “X” as we perceive the upper left side as continuing all the way to the lower right and the lower left all the way to the upper right.  Finally, in the fourth figure, we demonstrate closure, or our tendency to complete familiar objects that have gaps in them.  Even at first glance, we perceive a circle and a square.


We determine distance using two different cues: monocular and binocular.  Monocular cues are those cues which can be seen using only one eye.  They include size; texture, overlap shading, height, and clarity.

Size refers to the fact that larger images are perceived as closer to us, especially if the two images are of the same object.   The texture of objects tend to become smoother as the object gets farther away, suggesting that more detailed textured objects are closer.  Due to overlap, those objects covering part of another object is perceived as closer.  The shading or shadows of objects can give a clue to their distance, allowing closer objects to cast longer shadows which will overlap objects which are farther away.  Objects which are closer to the bottom of our visual field are seen as closer to us due to our perception of the horizon, where higher (height) means farther away.  Similar to texture, objects tend to get blurry as they get farther away.  Therefore, clearer images tend to be perceived as closer (clarity).

Binocular cues refer to those depth cues in which both eyes are needed to perceive.  There are two important binocular cues; convergence and retinal disparity.  Convergence refers to the fact that the closer an object, the more inward our eyes need to turn in order to focus.  The farther our eyes converge, the closer an object appears to be.  Since our eyes see two images which are then sent to our brains for interpretation, the distance between these two images, or their retinal disparity, provides another cue regarding the distance of the object.


An illusion is a perception that does not correspond to reality:  people think they see something when the reality is quite different, it’s the visual stimuli that “fool” or trick the eye.


For example figure 4,notice anything as you move your eyes over this image?  This image is not moving, seeing the “snakes” rotate is due at least in part to movements of your eyes.

Human perception of the world is obviously influenced by things such as culture and misinterpretations of cues.  Following are other factors that cause people to alter their perceptions.  People often misunderstand what is said to them because they were expecting to hear something else.  People’s tendency to perceive things a certain way because their previous experiences or expectations influence them is called perceptual set or perceptual expectancy.  Although expectancies can be useful in interpreting certain stimuli, they can also lead people down the wrong path.

For example, on figure 5 what do you see?

old lady

Some people can see a portrait of a young lady but some could only see a face of an old lady.


We have discovered earlier how sensation and perception works in our life and helps us see the world.  The same process with everyone else but why do we perceive the world differently.  This is because people’s behaviour is based on their perception on what reality is, not on reality of itself.

How do you see yourself?  How do you see the world around you?  How do others see you?  Do you take action based on your needs and goals, or is your behavior dependent on how you feel others will view you?  There are two types of perception; the way you see yourself and your world and the way others see you and their world.  The only perception you have control over is your own but it is impossible to control the perception of others.

So if you feel the urge to change other people’s behaviour, then it would seem that the most the most sensible place to start would be with changing yourself……  “The world as we have created it is a process of our thinking. It cannot be changed without changing our thinking.” Albert Einstein

According to David Schlundt, Psychologist at Vanderbilt University in Nashville, “You could look at a photograph and you would always be able to pick yourself out because we all have internal representations of what we look like”.   “But all of your experiences, all the teasing you went through as a child, all the self-consciousness you had as a teenager, and all the worrying about whether you would be accepted as good enough or attractive enough are called forth in” how people think of themselves, Schlundt said. “It’s not a perceptual thing. It’s a combination of emotion, meaning and experience that builds up over our lifetime and gets packaged into a self-schema.”

Our mind and thinking were mould by our ancestor, how we look and perceive everything around us, making sense of our world, forming judgements and opinions about every situations, event and interaction.  Those judgements and opinion will be affected by our central or core belief system, which influenced by our past experiences, childhood upbringing, culture, faith, values, current circumstances and our character traits (genetic influences).  Our opinions are driven by emotion mind, whereas reasonable mind is better able to see the facts and more aware of the bigger picture.

As we grow and learn more, our perspectives are changing.  Our learning and experience change through time, our expectation and perception changing from these.

Figure 7 – Our perception


Seeing different perspectives will help to reduce distressing emotions, help us feel more confident, enable us to be more understanding and emphatic, and improve communication and relationship.  As we challenge our unhelpful thoughts and biased perspectives, and see things in a more balanced and realistic way, so we discover that situations and people can be different to how we usually interpret things, which can lead us to modify our core belief system, and therefore bring about lasting positive change.  We look at things through the same two eyes but our perception make senses of the world we live in.

We live in our own world and how we want people to think or perceive you is impossible but we can stop worrying on what they might perceive or think about you.  To live in this world, full of different type of personalities, we need to learn to be considerate.  What others do or how they act is their choice, but it is up to each of us how we perceive their behaviour.   You will see in people whatever you unconsciously expect to see, and you will only perceive things that you have in you.   Whatever we each focus on, remember energy follows where your attention goes, we then project onto others in terms of how we want them to act.  Once your judgment of that person comes to your conscious attention, it is your projection.   So instead of judging other people, we can consider just do good to them and others will do good to us.


Sensations are the mind’s window to the world that exists around us.  Without sensations to tell us what is outside our own mental world, we would live entirely in our own minds, separate from one another and unable to find food or any other basics that sustain life.  Perception is the process of interpreting the sensations we experience so that we can act upon them, without perception, we would be unable to understand what all those sensations mean.

Over time, we are influence by our belief, our life experience, faith and cultures but as we grow, we learn to shape our own perception.  We living in a world but the world we have is how we look at things.  The world is internally, how we think and react in every situation.


Bryan Golden (Oct 20, 2011) Perception can influence you in many ways (ONLINE) Available : (February 20, 2016)
Dr. Christopher L. Heffner Chapter 5: Section 3: Perception (ONLINE) (March 10, 2016)
Emily Sohn (April 24, 2013) Why We Don’t See Ourselves as Others Do (ONLINE) Available : (March 1, 2016)
Gregg Henriques Ph.D. Theory of Knowledge (May 1, 2013) Perception and Perceptual Illusions. Psychology Today (ONLINE) Available:
Nedha (July 29, 2011) Difference Between Sensation and Perception. (online). perception/(February 27, 2015)

Natalie Wolchover  (October 04, 2012) How do Blind People Picture Reality? (ONLINE) (February 28, 2015)
S.Ciccarelli. White.J (2015). Psychology. Sensation and Perception (pg.125-167) 4th edition (global edition) Pearson. Essex England.
Weber’s Law of Just Noticeable Differences.(ONLINE). AVAILABLE: (March 20, 2016)
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