text: How we work out the distance of something we can hear but not see has been somewhat of a mystery - until now. Scientists say we know how far away the source of a sound is by listening to the echoes it produces. In a study they found that the reverberations of sound help us locate the distance of, for example, a car passing round a bend or a person nearby. Scientists at the University of Connecticut say we know how far away the source of a sound is by listening to the echoes it produces (stock image shown). In a study they found that the reverberation of sound helps us locate the distance of, for example, a car passing round a bend or a person nearby . The research was conducted by scientists from the University of Connecticut and published in the Journal of Neuroscience. They said that echoes and fluctuations in volume are the cues we use to figure out the distance between us and the source of a noise. Researchers have long understood how we can tell a sound's direction - whether it's to our left or right, front or back, and above or below us. From their heavy build and short limbs, to the shape of their skull and teeth, there are many ways that the anatomy of Neanderthals differed to our own. Now experts say that even a small bone in their ears are dissimilar to one in modern humans, raising the prospect that our extinct ancient relatives heard differently to us too. Researchers created a computer model of the middle ear bone of a Neanderthal child, whose remains were discovered in France 40 years ago. The remains from the two-year-old child, which are known as La Ferrassie 8, were discovered at La Ferrassie in the Dordogne, south western France, between 1970 and 1973. Asier Gómez-Olivencia, an Ikerbasque researcher at the University of the Basque Country in northern Spain, produced a 3D computer reconstruction of the remains. His work, published in The Journal of Human Evolution, reveals another anatomical difference between the Neanderthals and modern humans in the smallest ossicles of the body. But how we tell how far away it is had remained a mystery. 'The third dimension of sound location was pretty much unknown,' said Dr Duck Kim, a neuroscientist at UConn Health. The researchers suspected that the effect echoes had on volume - or amplitude modulation - could be key in our ability to perceive a sound's distance from us. To explore the idea, they used tiny microphones to record the sounds inside rabbits' ears as they played sounds at different locations. They used these recordings to simulate modulated or unmodulated noise coming from different distances from the rabbit. Then the researchers played the simulated sounds back to the rabbit, and measured the responses of neurons in the rabbit's inferior colliculus (IC), a region of the midbrain known to be important for sound perception. When the rabbit heard the simulated sounds, certain types of IC neurons fired more when the sound was closer - when there was a bigger difference between the sound's maximum and minimum volume. The farther away the source of a sound is from a listener, meanwhile, the more echoes there are, and the more limited the changes in volume become. As the source moved further away, therefore, the neurons fired less and less. The researchers say that the effect echoes have on volume - or amplitude modulation - could be key in our ability to perceive a sound's distance from us. Without amplitude modulation, for example in an anechoic (echo-free) room, pictured, a person can't tell how far away a noise is from them . The results suggest that, as a sound gets further away, our brains are able to work out the differences in its maximum and minimum volume - and thus its distance. Dr Pavel Zahorik, a researcher at the University of Louisville School of Medicine, got the same results with human volunteers. Without amplitude modulation, for example in an anechoic (echo-free) room, a person can't tell how far away that noise is. 'Reverberation is usually considered a bad thing,' detrimental to hearing clearly, said Dr Shigeyuki Kuwada, co-author on the University of Connecticut study. 'But it is necessary and beneficial in order to recognise distance.' The researchers hope to investigate the problem further, and  tie together the perception of distance, horizontal and vertical directions of sound.
target: University of Connecticut study reveals how we can measure distances .
  They said that listening to echoes tells us how far something it .
  When a sound is close the differences in max and min volume are obvious .
  But when it is distant, our neurons fire less, and we know it is further away .