Ask the expert

A woman sleeping on a bed.
A woman sleeping on a bed. PHOTO: ST FILE

Q: Why do some people dream in black and white?

A: It has been reported that a certain proportion of people dream only in black and white, and the number of people who do so has decreased noticeably nowadays, in comparison to the 1940s and 1950s.

For example, in a 1942 study, 70.7 per cent of 277 college students reported "never" or "rarely" seeing colours when dreaming. In contrast, only 17.7 per cent of 124 students reported this in a 2001 study which used identical methods.

It is still not clear why some people report not seeing colours in their dreams, and why the number of people reporting so has decreased drastically.

It is possible that people may have different assumptions about the presence or absence of colours in dreams, which in turn influence the colour contents of their dreams, or bias of their dream recalls.

People in the 1940s might have had the impression that dreams were supposed to be colourless and therefore under-reported colours when asked.

It is also possible that the increase in the reported colour of dreams comes from the influence of media such as colour movies, television, and photography.

• Assistant Professor Hsieh Po-Jang, Neuroscience and Behavioural Disorders Programme, Duke-NUS Graduate Medical School Singapore

• Have a burning science question? E-mail us at STscience@sph.com.sg

A version of this article appeared in the print edition of The Straits Times on September 18, 2015, with the headline 'Ask the expert'. Print Edition | Subscribe