Giving is a present in itself.

Temasek Polytechnic lecturer Emil Cheong, who teaches a diploma in psychology studies, said gift-giving may boost self-esteem.

"One gets to see and experience himself as a person with positive qualities, such as being generous or a good friend, which increases self-esteem."

Nanyang Technological University (NTU) psychology professor Albert Lee said the value of the gift is only part of the joy experienced.

"What is less apparent is the mental processes of mind perception behind this gift" - feeling important enough to receive a gift.

And for those who laugh at others who put up Christmas decorations too early, the joke is on them. Mr Cheong said perfecting the Christmas display may fulfil a need for achievement and recognition.

Another explanation for this comes from research on self-perception - which emphasises how people's own behaviour influences their feelings and attitudes, said Professor Lee.

"The fact that you bother to spend hours to shop for decorations and put them up suggests (to you) that you are probably in the mood for a nice holiday, and suggests a good quality of life." These associations are then reflected in a positive mood.

Having a live Christmas tree at home can add to the cheer and help overcome "mental fatigue and stress", said Dr Shawn Lum, a senior lecturer at NTU's Asian School of the Environment.

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Correction note: This story was edited for clarity.