TOKYO - Japanese researchers have invented a speech-jamming gadget that painlessly forces people into silence.

Kazutaka Kurihara of the National Institute of Advanced Industrial Science and Technology, and Koji Tsukada of Ochanomizu University, developed a portable "SpeechJammer" gun that can silence people more than 30 meters away.

The device works by recording its target's speech then firing their words back at them with a 0.2-second delay, which affects the brain's cognitive processes and causes speakers to stutter before silencing them completely.

Describing the device in their research paper, Kurihara and Tsukada wrote, "In general, human speech is jammed by giving back to the speakers their own utterances at a delay of a few hundred milliseconds. This effect can disturb people without any physical discomfort, and disappears immediately by stopping speaking."

They found that the device works better on people who were reading aloud than engaged in "spontaneous speech" and it cannot stop people making meaningless sounds, such as "ahhh," that are uttered over a long time period.

Kurihara and Tsukada suggested the speech-jamming gun could be used to hush noisy speakers in public libraries or to silence people in group discussions who interrupt other people's speeches.

"There are still many cases in which the negative aspects of speech become a barrier to the peaceful resolution of conflicts," the authors said.