Workings of the Inner Ear
Stereocilia, tiny hairs on the sensory cells of the inner ear, play a critical part in hearing: They move back and forth in a wave-like motion when stimulated by a sound wave. But a Swedish research team discovered that the hairs not only move sideways but also change in length, providing new fundamental knowledge about the mechanisms of hearing, and potentially leading to new treatments for impaired hearing.
It is impossible to study the movement of the human cilia because the sensory cells are deeply embedded in thick bone, but in guinea pigs and gerbils the inner ear is surrounded by thin bone. The scientists were able to observe the sound-induced ciliary motion using a specially designed microscope.
Previous studies revealed that sound causes a lateral movement of stereocilia, which creates the sensation of hearing. The study's results, presented in the online scientific journal Nature Communications, suggest the stereocilia's ability to change length was greater when the electric potential around the sensory cells was low, which happens in connection with noise damage and age-related hearing loss. The voltage drop causes the hairs to become overly soft, thus impairing ear function. Search doi: 10.1038/ncomms2100.
'Deafness Gene' for Usher Syndrome
Researchers at the University of Cincinnati and Cincinnati Children's Hospital Medical Center have found a new genetic mutation responsible for deafness and hearing loss associated with Usher syndrome (type 1). The findings could help researchers develop new therapeutic targets for those at risk for this syndrome.
Usher syndrome, a genetic defect, causes deafness, night-blindness, and loss of peripheral vision. Researchers performed a genetic analysis of 57 people from Pakistan and Turkey to pinpoint a protein, CIB2—found in stereocilia, the hair cells of the inner ear—which is associated with deafness in Usher syndrome (type 1) and nonsyndromic hearing loss.
Researchers believe the protein may be involved in calcium signaling that regulates mechano-electrical transduction, a process by which the ear converts mechanical energy into a form of energy that the brain can recognize as sound. The researchers believe the findings bring them a step closer to understanding the mechanism of mechano-electrical transduction and possibly finding a genetic target to prevent nonsyndromic deafness, as well as that associated with Usher syndrome type 1. Search doi: 10.1038/ng.2426.
Noise Bursts Affect Concentration
Noise can be distracting, especially to a person trying to concentrate on a difficult task. A study by researchers at the University of Nebraska-Lincoln noted a slight general trend toward lower performance when louder noises were played, and also identified sound level ranges that caused participants to report significant levels of annoyance.
To understand how short noise bursts affect people's mental state, researchers played quarter-second-long white noise clips to 27 participants as they worked on arithmetic problems, to see if they could find a threshold value under which the noise would not significantly affect their performance. Participants were asked to memorize six-digit numbers, and then, when shown a four-digit number, had to subtract the second number from the first number in their heads and type the answer on a keyboard. A quarter-second burst of noise would occasionally sound while the second number appeared on the screen.
Researchers tested noise bursts of approximately 50–80 dBA. Test subjects solved fewer problems correctly when interrupted by noise at the louder end of the spectrum, but the difference was not statistically significant. However, when quizzed afterwards, participants reported feeling significantly different levels of annoyance at the noises.
The motivation for the research came from NASA's low-boom supersonic aircraft program. Sonic booms, generated when aircraft traveling faster than the speed of sound leave cones of compressed air in their wake, are loud and potentially unnerving. Studying annoying noises helps architects design better building environments and policy-makers choose effective noise regulations. Study results suggest that acceptable noise from sonic booms should not be higher than 70 dBA once it gets inside someone's house.
Search "noise bursts arithmetic" at Newswise for more information.