The Müller-Lyer Illusion – A Research Activity

Handout for this activity

An explanation of this illusion on this blog

Our apparatus is shown below.

This design requires the use of a cut-up envelope. If you would like to use a variation of this design for your own perceptual experiment, I recommend that you create a similar apparatus, perhaps with an alternative version of the illusion.











Possible Hypotheses:

Hypothesis 1: Since participants will perceive the line with V-shaped ends (Line B) as longer than the line with arrowheads (Line A), they will draw out the card depicting Line B to a length less than the length of Line A (10 cm).
Hypothesis 2: Since participants are aware of the potential illusory influence of the two lines, they will try to compensate for the power of the illusion and draw out Line B more, on average, with each succeeding trial.

To go further:

Alternative explanations of the illusion from VeryWellMind

Alternative explanations of the illusion and recent studies from The Illusions Index

Print Friendly, PDF & Email

Perceptual Set/Expectancy

My husband can recognise individual countries in Africa just from their contours. His love of maps and experience in reading them lead to a perceptual set that enhances his skill in this kind of perceptual task.

Experience makes us more efficient and predictive perceivers. My husband, for instance, spends hours poring over maps; as a result, he can recognise several seas and countries by their contours alone. In my role as an English teacher, I have read so many student texts that I can identify misspelt words more swiftly than my husband, who as a Maths teacher has developed other (possibly more useful) perceptual abilities. In the same way, a person who takes an interest in a particular brand of clothing can recognise another person wearing that brand, even from a distance. These are all examples of how one’s emotions, motivation, training and experience can influence one’s perceptual set. Another term for this is perceptual expectancy.

Perceptual set refers to a readiness or a predisposition to perceive a visual stimulus in a particular way. Your background, knowledge, motivation and emotions all affect what you pay attention to, which features of a stimulus you focus on and, conversely, which details you ignore. You bring your own expectations to any perceptual task; the context in which you view the stimulus also plays a role. All of these factors allow you to formulate perceptual hypotheses more quickly and accurately, which influences your interpretation of the scene before you and generally enhances your perceptual skill.

For example, in the visual stimulus below, you presumably perceive a horse.

It’s a horse. Or is it?

The following picture, however, provides more context. When you look at it, assuming that you have experience of chess and can therefore be influenced by the other figures surrounding the “horse”, you are likely to perceive a “knight”. In this case, both the context provided and your cultural and educational experience work together to influence your perception of the stimulus and your interpretation of its meaning.

Well, yes, it’s a horse. Yet in this context, it’s also a knight. 

Class presentation on this topic

Questions and Key Terms

a Write a definition of perceptual set. (See my presentation and your text.)
b List the factors that influence perceptual set and provide an example for two of these factors.
c Identify a perceptual set that influences your interpretation of a particular visual scene. Use key terms in your explanation of your perceptual set example.

Suggested key phrases for (c)
►I have a perceptual set as a result of my interest in…
►As a result of my prior experience and training, I…
►I tend to pay visual attention to…
►I focus on certain features of the visual sensory data, namely…
►I am able to formulate rapid and accurate perceptual hypotheses about…
►My motivation and my emotions also play a role, because they influence my attention to…

Print Friendly, PDF & Email

Perceiving Depth

relative size, height in the visual field

light and shadow

linear perspective, texture gradient

linear perspective, texture gradient

♦ Handout: Depth principles – blank

♦ Handout: Depth principles – answers

♦ Interactive quiz: Cues to depth 

Tiny Cards: Overview of sensation and perception

Kahoot: Perceptual principles → With others | Alone

Quiz: Categories and depth principles

To go further:

Article: Perception of depth from Webvision

Print Friendly, PDF & Email

The Gestalt Principles

The word “Gestalt” means “figure”, “form” or “shape”. For the Gestaltist school of thinkers, an organised whole was more than the sum of its parts.

In other words, the Gestaltists believed that human perceivers search for whole forms in any perceptual endeavour. We seek coherence, order and meaning. We look for the complete entity that can be discerned in a stimulus, rather than focusing on the fragmentary elements that make up the visual scene.

Notice my teacup, for instance: you perceive it as a whole, connected object, not as a number of disjointed parts; yet the main component, the bowl shape, does not actually exist at the sensory level. There is nothing there for your sensory receptors to detect, yet your brain still manages to perceive it.

The Gestalts believed that our brains apply certain rules or principles in order to organise the elements from any visual scene or stimulus into a cohesive whole. 

Revision quiz on eye structures and their functions

Quiz on the Gestaltists and their main principles

♦ Kahoot on sensation and perception: Preview Mode | Class Mode

To go further:

An absorbing account of the Gestalt principles and their applications in art, advertising and design

Print Friendly, PDF & Email

A Perceptual Walk

Class Activity Handout: Catch yourself in the act of perceiving


♦ Task: Use this diagram (public domain from here) and your text to create a set of notes on the functions of each structure in the eye.

♦ To go further:

More about the human eye on this blog 

Crash Course: Vision

An excerpt from The Man Who Mistook His Wife for a Hat by Oliver Sacks


Is it a rose or, as Dr P. referred to it in the intriguing account by Oliver Sacks, “a convoluted red form with a linear green attachment”?


Visual stimuli for class activity: rose, snow mystery, coffee, brain tree, scrambled, neglect, Rubin, cube, partial faces, wild animals

Print Friendly, PDF & Email

Distinguishing Sensation and Perception

Mental Health, Mental Illness and Classification

Dear Year 11 students,

As you can appreciate, defining any set of complex human behaviours is a complicated operation. Since the topic of mental illness has often been plagued by entrenched prejudices and social stigmas, the labelling of a mental disorder is particularly open to dispute. The Diagnostic and Statistical Manual of the American Psychiatric Association has been revised and updated several times and is nevertheless open to development and improvement. In this task, you will have the opportunity to delve into the categories of mental illnesses as defined in the DSM and select a single disorder for closer study. I hope you find this challenging and worthwhile.

Kind regards,

Ms Green



Handouts and Activities

Print Friendly, PDF & Email

Research Investigation – Unit 1, 2017

Online Activities

Handy Downloads

Dear Year 11 Psychology students,

Welcome to the new school year. Thank you for choosing the subject of Psychology, with its rewarding mixture of human stories and scientific research. 

The “Research Investigation” (Area of Study 3) is a challenging task. The main rule is: don’t panic. This assignment is all about learning and exploring the diverse field of psychology that you have chosen to study. Select a topic that you find interesting and then enjoy deepening your knowledge.

Break complicated tasks into parcels…

Most important of all, avoid stress by breaking the task into small, manageable parcels of work. Tackle your workload in do-able chunks; this approach will help you in other subjects as well. Following these instructions should help:

♦Chunk 1: Select a key study that interests you. See the long list of links below our instructions for ideas and starting points. There is also a “pinboard” that will allow you to visualise the range of possibilities. Feel free to search for and contemplate other options as well.

♦Chunk 2: Write an open research question that relates to your key study. Here are some examples of appropriate wording, in which we have employed phrasing that requires exploration of possibilities, rather than a closed, yes-no answer: 

  • How does stress influence the ageing of the brain?
  • To what extent and in what circumstances is multi-tasking possible?
  • How does the use of marijuana affect the social and cognitive development of teenagers?
  • In what ways (if any) does stress affect women differently from men?
  • In what ways can biofeedback benefit people’s health?
  • How does learning change the physical structure of the brain?

♦Chunk 3: Find another, related study on a similar topic. This will allow you to extend your writing and contemplate another perspective. If you are able to find two related studies, that would be ideal.


Finally, here is a handy plug-in and/or app that can be used on laptops, smartphones or tablets: Pocket allows you to save all the articles you find and so maintain an online digital logbook of your reading, accessible on all your devices: iOS | Android | Chrome | Safari. This could be useful in other subjects as well. 

Kind regards from Ms Green, Ms Corbo and Ms Bottrell

Useful websites for independent exploration:

Brain and Behaviour Research Foundation 

Forbes: Top 10 Psychology and Brain Science Studies of 2015 (see links to earlier years as well)

Links to specific subjects and studies:







Click here to view the pinboard below on the whole screen
Psychology – Research Investigation


Print Friendly, PDF & Email

People in Groups

Group of diverse students

People in groups act in strange, counter-intuitive and sometimes disturbing ways. The reasons for this are complicated, to say the least. It appears that being in a group reduces one’s sense of responsibility and intensifies one’s inhibitions while simultaneously increasing one’s sense of anonymity. While these tendencies do not necessarily allow us to predict a single individual’s behaviour in a group, certain patterns of behaviour emerge when groups are studied as a whole. For instance, helping behaviour tends to be reduced as the size of a group increases. Bystanders are more likely to be helpful if there are fewer of them. This is known as the bystander effect.

Another example of the surprising effects of group membership is the tendency to conform, that is, to do what others do or say what others say, even when this goes against one’s own judgement; to ensure that one’s own attitudes, reactions and beliefs adhere to group norms

Girls conformityFor instance, Asch (1951) illustrated through his supposed “line perception task” that about 33% of participants, after observing a number of confederates uniformly giving the wrong answer, conformed with the judgement of the majority. The mistake of the confederates was obvious, yet their unanimity moved the real participants in a substantial number of cases to conform, despite the evidence of their own eyes. Although this study’s findings are open to question for several reasons, conformity as a form of social influence is clearly an important topic of study in psychology.

How we perceive people in groups is also potentially problematic. While stereotyping people in groups can allow swift and even accurate judgements in social situations, it can also lead to prejudice if our stereotypes are too rigidly applied or overly simplistic. For instance, the stereotype of “doctor – white coat – expert” could be useful in determining which person to ask a question when you enter Casualty at a major hospital. On the other hand, if one persists in the belief that all people from a particular social group are snobbish or, worse, somehow inferior, it may become impossible to develop friendships, break down prejudice, engender understanding or accept diverse views. 

Watchrat facing right


  • Asch (1951): Classic conformity study from – an excellent account that outlines the limitations of the study as well as its findings



Print Friendly, PDF & Email

Sensation and Perception

teacup turquoise
The sensory data that are normally required to see a cup are not present in this stimulus – and yet we perceive a cup. Would we perceive it if we hadn’t been raised in a coffee-drinking society?

We tend to assume in everyday life that we perceive the outside world exactly as it is. In reality, however, there are many physical energies that we are not equipped to detect. Furthermore, we organise and interpret the information we receive based on our past experience and other psychological factors. Our perceptions are therefore our own personal representations of the physical energies that batter our senses at every turn.

The sensory data that our sensory organs receive are at that stage meaningless; only when our brain receives the electrochemical energy that is sent to it from each set of sensory receptors can we begin to organise this information and make sense of the bewildering environment around us.

Yet every day we conjure meaning from the cacophony of sound, the blazes and flickers of light, the chemical compounds and the physical taps, nudges and thumps that we encounter. This is an indication of our astonishing perceptual gifts, yet in some respects I find the perceptual oddities and surprises, along with the errors that we make, more intriguing. Mistakes are always more revealing than perfection.

– Ms Green

book2, clipartlord, pdRead

television with play button







Examples of Visual Stimuli

Bec, Emily and James

This stimulus illustrates the Gestalt principle of closure, since most English speakers can read it despite the missing elements. (Designed by Bec, James and Emily)

clock by ngoc

Ngoc designed this visual stimulus to illustrate the principle of closure. You could also argue that the principle of similarity is at work.

Convergence and Retinal Disparity two times Roslyn Green

How retinal disparity works: If you focus on my two faces from a distance of 5-10 centimetres (crossing your eyes slightly might help), you may discover after a while that you have fused the two images into another, spookily three-dimensional one in the middle. This procedure works better when the image is on paper, so you can also try printing this version: download paper version here.

teacups improved gestalt similarity

This stimulus illustrates the Gestalt principle of similarity. We perceive the red saucers and their “cups” as belonging to a group.

gestalt proximity

We perceive  the the dots as columns rather than rows as a result of the Gestalt principle of similarity.

Green illusion

An illusion: In the context of the gradual change of colour gradient in the background rectangle, the block of green in the foreground is perceived as having a gradual colour gradient too, yet in reality it is a solid block of colour like the green rod at the bottom.

Jesus in snow drawn by me

If you perceive this as a man’s face, you must be applying the Gestalt principles of figure-ground and closure at least. If you interpret the face as that of Jesus, then your cultural background or artistic experience is also coming into play and influencing your perception. (This is a simplified version of the original stimulus, which may be viewed here.)

FullSizeRender (13)

This stimulus, designed by Jude, can be organised and interpreted in more than one way, as either a mouth with rather narrow teeth or as a forest behind a meadow. You notice yourself switching back and forth between the alternative interpretations, which indicates that this is a successful ambiguous stimulus. Would you be more likely to perceive a mouth if you had just kissed someone? Would you be more likely to see the trees if you were a nature-lover?

Sam boat Sam alien

Sam’s stimulus is organised and interpreted differently, depending on which way up you look at it. The figure on the left could be a boat in rocky waters, while the figure on the right could be an alien – or a psychology teacher.


Kate’s stimulus provides an example of the principle of closure. We perceive a head, a face and dark glasses, even though none of these features is completely represented.


Althea’s visual stimulus is perceived as complete circles and lines, even though none of the circles have a complete contour. This demonstrates once more our tendency to apply the closure principle in order to perceive wholes.


Print Friendly, PDF & Email