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’s 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’s application was filed by the US Navy in 2019 and it isn’t clear whether the device has been built or tested yet.
A was tested by researchers at Japan’s National Institute of Advanced Industrial Science and Technology in Tokyo with the aim of “controlling and facilitating discussions”, but didn’t advance beyond the lab.
, a cognitive neuroscientist at University College London, says that delayed feedback interferes with a speaker’s 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. “It will be very incapacitating for a handful of people, but by no means everyone,” 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 milliseconds, 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 milliseconds, 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 be heard. But as well as not working on everyone, for some, it might actually have the opposite effect. “The paradox
is that it might make some people more fluent,” says Scott.
Delayed auditory feedback can be an for people who stammer. The exact reasons aren’t well understood, but it seems to relate to how the brain handles feedback.
Scott is concerned that the development of Brown’s device could prevent people speaking out. “The desire to stop people from talking is chilling,” she says.
