Afterimages
PERCEIVING COLOURS:
Colour Interactions
Explore afterimages
Details:
All ages
Time: 15 minutes
Learning Outcomes: Experience afterimage with one and both eyes.
Describe the difference between a colour and its afterimage.
Colour Concepts: Recognize that afterimages result from adaption in the retina.
Materials:
Crayon (or marker, or pencil crayon - something to colour in a space)
Instructions:
Choose one coloured crayon (or pencil crayon etc.) and fill in the top circle on the left.
Stare at the black dot inside the coloured circle for 30 seconds, then shift your focus to the black dot inside the white circle below your coloured circle.
What colour do you see? This is the afterimage colour of your coloured crayon.
Find the crayon colour that is the closest match to the afterimage's colour, and fill in the top middle circle.
Close or cover your left eye and repeat the second step above.
Now close or cover your right eye, and look at the white circle below.
What do you notice?
Vocabulary:
Questions & observations:
What is the relationship between a colour and the colour of its afterimage?
What does doing this exercise with one eye tell you about afterimages?
Can you take a photograph of an afterimage? Why?
More to explore:
Repeat the exercise on the top right circle using a different coloured crayon.
What’s going on?
Afterimages are complex physiological experiences, which result from the colour receptors in our eyes (i.e. our cones) adapting to the visual environment. If one eye is covered and does not receive a visual stimulus, it will not generate an afterimage.
Afterimages are entirely experiential, and cannot be photographed.
A colour and its afterimage colour define one type of complementary pair (but there are other ways to describe complements). The afterimage experienced in this exercise is more precisely known as a negative afterimage. See the glossary page for more information about negative afterimages.
Find out more:
See the Exploratorium Exercise on Negative afterimages (‘Bird in a Cage’)
See the Exploratorium Exercise on Positive afterimages
