When a number of US diplomats and their families in Cuba reported hearing bizarre noises in 2016 and 2017-- and experienced a range of symptoms such as dizziness, vertigo, and pain and ringing in the ears -- US Department of State officials feared they might have fallen victim to an "acoustic attack" by sonic devices.
In October 2017, the Associated Press obtained and released the first publicly reported audio sample said to be related to the incidents. But US officials have been unable to definitively identify the source or cause of the symptoms, and Cuban officials have denied any attack.
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But now, after analyzing the recording, scientists say the source of the piercing noise said to be a "sonic attack" -- described by the diplomats' as "buzzing," "grinding metal" and "piercing squeals" -- could be an echoing call of a cricket. Specifically, the Indies short-tailed cricket, Anurogryllus celerinictus.
In research released on January 4, a British and an American scientist said the cricket's chirps matched "in nuanced detail, the AP recording in duration, pulse repetition rate, power spectrum, pulse rate stability, and oscillations per pulse." The research has not been peer-reviewed.
The scientists said inconsistencies in the AP-released recording might be because it was made indoors, while insects are typically recorded in the field, they wrote.
"The AP recording also exhibits frequency decay in individual pulses, a distinct acoustic signature of cricket sound production," wrote the scientists, Fernando Montealegre-Zapata, a professor of sensory biology at the University of Lincoln in the UK, and Alexander Stubbs of the University of California, Berkeley.
Although the sound on the AP recording comes from a Caribbean cricket, the scientists did not rule out "the possibility that embassy personnel were victims of another form of attack." Nor does it rule out that the diplomats' symptoms were psychosomatic, adding that their health problems were beyond the paper's scope.
A State Department spokesperson told CNN that "a US government interagency investigation, involving medical, scientific, and technical experts across the US government and academia, is ongoing to determine the source and cause of these events."
"The safety and security of US personnel, their families, and US citizens abroad is and has always been the Department of State's top priority," the spokesperson said.
No culprit found
There have been a number of studies looking into the possible causes and symptoms of the noises heard by US officials.
A study published in the medical journal JAMA in March 2018 described the symptoms of 21 personnel who sought medical attention and found that a majority of them reported problems with memory, concentration, balance, eyesight, hearing, sleeping or headaches that lasted more than three months.
Three people eventually needed hearing aids for moderate to severe hearing loss, and others had ringing or pressure in their ears, according to that report.
A study last month detailed the symptoms experienced by 15 men and 10 women. It noted that some of the findings may seem similar to symptoms of a "mild traumatic brain injury following blast exposure or blunt trauma."
The US Department of State and federal investigators have been unable to definitively identify the source or cause of these symptoms.
Cuban officials have denied any targeted attacks on diplomats in Havana and said the symptoms could have been caused by other factors.
"All has been speculation or manipulated information," Cuba's Director General for US Affairs at the Cuban Foreign Ministry, Carlos Fernandez de Cossio, said December about the US investigation into the incidents.
"The concrete questions have not been asked. Why has the US government not been ready to cooperate with Cuba? What is the US government hiding? Why is it not capable of putting forward concrete, real information that the scientific community can accept?"
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