Can You Hear Me Now?

 

Lombard - Split Second Act from Ear to Brain –

It has been observed that humans as well as animals while trying to be heard over sound tend to raise their voices. It is said to be a split-second act from the ear to the brain for vocalization. The first to measure how fast it tends to occur in bats – 30 milliseconds, are researchers from Johns Hopkins University. This is 10 times quicker than the blink of an eye, a record for audio vocal response.

 Since this deed is known as the Lombard, its effect tends to take place very fast; the researchers were capable of solving a long overdue mystery considering the neural mechanism behind it. Recently in a paper publishing in the journal `Proceedings of the National Academy of Sciences’, they concluded that it could be a fundamental temporal reflex instead of a deeper, thinking behaviour as presumed earlier, which would be time consuming in processing.

The discoveries shedding light on the foundations of human speech control has also disclosed how species as diverse as fish, animals, and frogs together with humans tend to share the ability to be head over the fight. Co-author Ninad Kothari, a graduate student in Psychological and Brain Sciences at Johns Hopkins stated that scientist have been speculating for a century that, could there be a common auditory process in explaining how this phenomenon occurred in fish to frogs to birds to human species with wildly various hearing systems and they had resolved this question.

Lombard Effect

The new statistics could lead to improved treatment for diseases and the Lombard effect could be intensified like Parkinson’s disease as well as support in building assistive medical devices. Studies conducted on bats, animals which tend to depend on sonar-like echolocation, releasing sounds and listening for echoes in order to sense, track and catch prey, had been carried out by the researchers.

In contrast to humans, where the vocalization tends to be reasonably long and slow, bats seems to be perfect for such sensorimotor study since their extraordinary frequency chirps, unnoticeable to the human ear are said to be quick and accurate enabling the researchers to test the parameters of a mammalian brain.

While tracking an insect moving towards the animal on a tether, the team had trained big brown bats to stay balanced on a platform and while the bat hunted for the insect, the researchers had recorded the vocalization of the bat with an array of 14 microphones. The researchers at time permitted the bat to hunt in silence while at other times they played bursts of interfering white noise at different intensities from a speaker which has been placed in front of the bat.

Brain Monitors Background Noise Continuously

It was observed that the white noise had interfered with the echolocation of the bat and had caused the bat to emit louder and louder chirps not different from two neighbours attempting in making a conversation, first over a lurid radio and then over the clamour of a lawn mower and thereafter over the blast of a passing fire engine.

When the noise had stopped, the bat would also stop shouting, to speak and voice at a more usual level. The researchers capable of creating a computational model for the Lombard effect which tends to be applicable to all vertebrate, reached a conclusion that the brain of a bat or a person or a fish tends to monitor continuously the background noise and is inclined to adjust the vocal levels whenever the need arises.

 At first the auditory system is said to notice the background noise. Then the auditory system measures the level of sound pressure and tends to adjust the vocalization amplitude in order to compensate and when the background noise stops, the sound pressure level dissipates as well as the level of vocalization.

Connection Between Hearing & Vocalizations

The author observed that this complete intricate process tends to take place in only 30 milliseconds. In terms of near-instantaneous brain reactions, they name this reflex as `remarkably short’. Lead author Jinhong Luo, a Johns Hopkins postdoctoral colleague had stated that `typically, we breathe every three to five seconds, our heart beats once per second and eye blinking takes one third of a second.

If we believe that eye blinking is fast, the speed at which an echolocating bat responds to ambient noise is truly shocking – 10 times quicker than we blink our eyes’. Scientists are of the belief that the Lombard effect seems to be much slower, around 150 to 175 milliseconds for humans.

Johns Hopkins professor of Psychological and Brian Sciences and Neuroscience and a co-author, Cynthia Moss commented that their study features echolocating bats as valuable animal models for understanding connections between hearing and vocalizations, including speech control in humans.

 The research has been supported by the national Science foundation IOS-1010193 and IOS-1460149, the Human Frontiers Science Program RGP0040 and LT000279/2016-L, the Office of Naval Research N00014-12-1-0339 and the Air Force Office of Scientific Research FA9550-14-1-0398