If the price of a product is reduced, willingness to buy increases – the product appears cheaper even though it is perhaps still too expensive. Our perception of the world is therefore often relative: we compare what we see with a reference point – in this case with the price before the discount. The same applies to the perception of luminance stimuli. An object appears brighter if the background is dark, and darker if the background is bright. Optical illusions help to analyze the perception of such relative contrast signals. What happens, however, at cellular level in the brain is largely unknown. Scientists at the Max Planck Institute of Neurobiology in Martinsried have now used behavioural experiments on the fruit fly Drosophila to show that spatial contrast information and motion stimuli are processed in different neural circuits.
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