An Introduction to Perception

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, the perceptual oddities and surprises, along with the errors that we make, are more intriguing. 

Starter Quiz – with Explanations

Reading Options

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”? →




More Activities


Handouts and Presentations

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.)


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