Can't be bothered to show anyone what you're thinking? Then a Japanese scientist has the answer -- a pair of digital eyes that can express delight and anger, or even feign boredom.

Building on a long line of slightly wacky and not-very-practical inventions for which Japan is famous, Hirotaka Osawa has unveiled the "AgencyGlass".

"I wanted to build a system that is capable of carrying out social behaviours for humans," he told AFP.

Just as robots can reduce the need for physical labour, the AgencyGlass -- which looks like two small TV screens set in spectacle frames -- aims to cut down its user's emotional demands by carrying out their eye movements for them.

The two organic light-emitting diode (OLED) screens, which are connected to motion sensors and an external camera, show a pair of eyeballs that can appear to be making eye contact while the wearer is looking somewhere else entirely.

The wearer has to choose their emotion in advance -- if they want to appear "attentive", for example, they must switch it to this mode before putting the glasses on.

Osawa, of the prestigious Tsukuba University, said possible applications include for flight attendants dealing with irritating passengers, or teachers who want to project an image of kindness towards shy students.

"As the service sector grows and becomes more sophisticated, it becomes increasingly important that we behave by showing understanding to others," he said. "That requires us to behave differently from our true feelings."

Such "emotional labour" has caused some people to become deeply conflicted and develop emotional illnesses, Osawa said, adding that his technology could eventually help them.

The glasses weigh around 100 grams (3.5 onces) with the battery lasting roughly an hour, Osawa said, adding that the prototype cost just over 30,000 yen ($290) to make. They are currently not in production.