In 1895, the English toymaker and amateur scientist Charles Benham produced a top with a monochrome pattern that, when spun, causes colours to be seen at different places on the disc. He sold it as the ‘Artificial Spectrum Top’.
The previous year he had relayed observation of the phenomenon in an article in the journal Nature, writing that it furnished ‘an interesting phenomenon to students of physiological optics’. Benham had been inspired by the German psychologist Gustav Fechner, who had experimented with similar spinning discs and recorded their effects.
Scientists have offered various explanations for the ‘artificial’ colours. One is that they are a result of receptors in the eye sending confused signals to the brain. The white part activates colour receptors in the retina and the black part deactivates them, but different cells have different response times, resulting in a lag in signalling from the colour receptors, causing perception of colour.
Another theory is that the black and white areas activate neighbouring parts of the retina - colours being generated by the resulting ‘clash’ in the nervous system.
The perception of colours in Benham’s top is not the same for everyone. Different people see different shades in the same disc. But when its spinning direction is reversed, or when the disc accelerates or decelerates, a change in colours is perceived universally.
Benham’s top was both a popular toy and a tool for investigating the human visual system, with scientists using modified and motorised versions of it in experiments well into the 20th-century, before being replaced by more powerful stroboscopic light.
If you would like your experience to be shared in the virtual and live exhibition, please send a written description and/or a drawing of your experience to Dr Reeder at firstname.lastname@example.org