A non-lethal device developed by the US Navy aims to surreptitiously render a person unable to speak.
The device, called a handheld acoustic hailing and disruption (AHAD) system, records a target鈥檚 speech with a long-range microphone and plays it back to them with a tiny delay. As anyone who has spoken on a phone or internet call that echoes their voice back at them will know only too well, such delayed auditory feedback can be highly disruptive to speech.
The device is granted this month to Christopher Brown at the Naval Surface Warfare Center, Crane division, near Bloomington, Indiana.
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It beams back two versions of the recorded speech, one with a slight delay. The patent suggests using a parametric speaker, which emits directional sound so that only people who are targeted can hear it. This makes it inaudible to anyone else, so as far as any bystanders can tell, the target will seem to have trouble speaking for no obvious reason.
The patent鈥檚 application was filed by the US Navy in 2019 and it isn鈥檛 clear whether the device has been built or tested yet.
A was tested by researchers at Japan鈥檚 National Institute of Advanced Industrial Science and Technology in Tokyo with the aim of 鈥渃ontrolling and facilitating discussions鈥�, but didn鈥檛 advance beyond the lab.
, a cognitive neuroscientist at University College London, says that delayed feedback interferes with a speaker鈥檚 ability to control their voice. Some people simply stop talking, some find their speech distorted with lengthened vowel sounds, while others might start stammering. However, there are people who seem able to carry on regardless. 鈥淚t will be very incapacitating for a handful of people, but by no means everyone,鈥� says Scott.
Some individuals, probably those used to speaking to crowds and in varied acoustic environments, can continue to talk through the disruption. There is a risk that the presumed targets, public speakers, are those least likely to be affected, she says.
Scott says auditory feedback causes the most disruption when the delay in playback is about 200鈥塵illiseconds, roughly the typical time it takes to speak one syllable. With AHAD, there will be an additional delay due to the distance the sound travels. If the device was more than 30 metres away from the target, this will be more than 200鈥塵illiseconds, reducing its effectiveness.
The US Navy has already pioneered the use of long-range acoustic devices, powerful speakers used for or for to disperse crowds.
By contrast, the new AHAD may operate at low volume. Scott says that delayed auditory feedback can disrupt speech even if it is just loud enough to聽be heard. But as well as not working on everyone, for some, it might actually have the opposite effect. 鈥淭he paradox
is that it might make some people more fluent,鈥� says Scott.
Delayed auditory feedback can be an for people who stammer. The exact reasons aren鈥檛 well understood, but it seems to relate to how the brain handles feedback.
Scott is concerned that the development of Brown鈥檚 device could prevent people speaking out. 鈥淭he desire to stop people from talking is chilling,鈥� she says.
