Video: Stare hard at the spiral. Does it affect how you perceive the woman? If you don鈥檛 see it first time, try watching again in full screen.
Swirling spirals and a feminine eye might remind you of the title sequence of Alfred Hitchcock鈥檚 Vertigo, but now psychologists are using those same images to investigate the rules of attraction.
In the video above, created by Clare Sutherland and from the University of Glasgow, UK, a woman鈥檚 pupil appears to dilate, even though the image is a still photograph. The trick is down to a powerful after-effect caused by staring at a rotating spiral, positioned in exactly the same part of the screen as the pupil, before seeing the photograph of the woman.
The direction of rotation can cause the opposite effect in the pupil: if the spiral rotates 鈥渋nwards鈥�, the pupil will appear to dilate, whereas an 鈥渆xpanding鈥� spiral will cause the pupil to apparently contract.
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This mind trick 鈥� called the Belladonna effect 鈥� is helping the team鈥檚 research into attractiveness. Large pupils is a known signal of physiological arousal, say the authors, so they predicted that making the pupils seem dilated would make a face appear more attractive.
To test this theory, 40 volunteers were asked to rate the attractiveness of women in nine photographs after the illusion was used to make the women鈥檚 pupils appear to contract or expand. 鈥淲e found that ratings were reliably higher in the expanding-pupil condition than in the contracting-pupil condition, demonstrating for the first time an illusory Belladonna effect for physically identical stimuli,鈥� say the researchers.
Read more: Moving illusions: Brain-tricking motion