28 November 2011

Watch Out For These Noisy Toys

December is the biggest toy-buying month of the year. Unfortunately, many well-intentioned parents may be purchasing potentially harmful toys for their children. Any sound above 85 decibels (dB) can cause hearing loss over time.

The danger with noisy toys is greater than the sound level they produce implies. Children often hold toys directly to their ears which actually exposes them to more sound. A toy rated at 90dB can produce as much as 120 dB of sound at the ear, the equivalent of a jet plane taking off. Noise at this level is painful and can result in permanent hearing loss.

Every year the Sight & Hearing Association and researchers from the University of Minnesota test a variety of toys for potentially dangerous noise levels. This year, 19 of 24 toys tested produced sounds in excess of 100 dB. That's louder than a chainsaw! Workers would have to wear hearing protection for similar noisy sounds on the job.

This year's top offender was Disney's Cars 2 Shake n Go! Finn McMissile car, blaring at 124 dB, loud enough to risk instant hearing damage. Number two was another Disney product, Princess Video Play-a-Sound Follow Your Dreams book coming in at 118 dB. For the complete list, visit Sight & Hearing Association.

To protect your children, follow these tips:
  • Before purchasing a new toy, listen to it. If a toy sounds loud, don't buy it
  • Check the toys you already have at home. Remove the batteries or put masking or duct tape over the speakers of noisy toys. This will help reduce their volume.
  • Look for toys that have a volume control or an option to mute the volume.
  • Report loud toys. Contact the Consumer Product Safety Commission or the Sight & Hearing Association.
Remember, your child's hearing is precious (just like them!).

05 July 2011

Why Are Certain Sounds Annoying?

I'm currently reading a fascinating book, "Annoying: The Science of What Bugs Us" by Joe Palca and Flora Lichtman. The two science journalists take a look at the literature in various disciplines (psychology, evolutionary biology, anthropology and others) to try to discover why certain things drive us crazy.

Of course, I was drawn to the chapter on annoying sounds, with no surprise that fingernails on a chalkboard clocked in as the number one annoyance as compared to others sounds. Various researchers have attempted to discover what it is about this particular sound that makes it so irritating. First, they filtered the high frequencies of the fingernail sound (their hypothesis was that high-pitched, "screechy" frequencies might be to blame). Surprisingly this only muffled the sound but did nothing to make it more pleasant. When they filtered the frequencies from 500Hz to 2000Hz, that did the trick.

A few reasons why this is important:
  • The human ear can detect frequencies between 2000Hz and 5000Hz at lower volumes than other frequencies, which is good because this is where most of the important sounds of speech fall.
  • The ear is most sensitive to noise loss between 2000Hz and 5000Hz, so one hypothesis is that this is ear preservation in action. The most sensible way to protect hearing is to develop an aversion to damaging sounds.
  • The natural resonant frequency of the average adult ear canal is around 3000Hz.
  • Interestingly, the researchers found that the sound with the most amount of energy at 3000Hz is a human scream (men also scream at 3000Hz, since they break into falsetto). Babies cry at this frequency, and alarms are also often at 3000Hz.
So the sound that we can detect at the greatest distance is a scream, and when the energy the human ear is most sensitive to is removed from the fingernail sound, it's easier to ignore.

Another factor that may contribute to the fingernail sound being annoying is that it is more rough (a subjective perception of rapid amplitude modulation). Basically, the fingernail grabs the surface of the slate, and as you continue to move your hand down it's stuck and then suddenly will slip and jump to the next position. This produces a highly unpredictable, varied sound. The roughness is what seems to make people cringe the most.

Just some things to think about next time you hear that annoying screech!

18 September 2009

Hearing Aids & Cell Phones

If you wear hearing aids, you may experience audible interference when using a digital wireless telephone due to radio frequency (RF) emissions from the phone, regardless of whether the microphone or telecoil settings on the hearing aids are used.

As a result, when you hold a cell phone (or other wireless device) up to your hearing aid, you often hear annoying interference. This interference can make understanding speech difficult, communication over cell phones annoying and—in the most severe cases—render the phone completely unusable to the hearing aid wearer.

Fortunately, new rules adopted by the Federal Communications Commission (FCC) require cell phone makers and service providers to make phones work better for people using hearing aids and cochlear implants. These rules require:

• Less static
• Less interference
• Better telecoil connections

The FCC defines Hearing Aid Compatibility (HAC) for cell phones in terms of radio-frequency (RF) emissions—the "M" (microphone) rating, and the "T" (telecoil) rating. The rating scale ranges from 1 to 4. The higher the “M” rating, the less likely the hearing aid user will experience interference when the hearing aid is set in the microphone mode while using the cell phone. A higher M number means the phone will sound clearer.

If you have a hearing aid or cochlear implant with a telecoil, look for a phone that has a telecoil (T) rating of T3 or T4. The higher the “T” rating, the less likely the hearing aid user will experience interference when the hearing aid is set in the telecoil mode while using the cell phone. A higher T rating will make your conversations clearer.

Thus, if you use your cell phone while wearing your hearing aids in the microphone ("M") mode, look for one that is rated M3 or M4. If you use your cell phone while wearing your hearing aids in t-coil ("T") mode, look for a phone that is rated T3 or T4. (T4 is better.) The higher the rating, the less likely it is that you will experience interference.

22 April 2009

Florida Manatees: Silent Danger

The endangered Florida manatee, Florida’s state marine mammal, is a large aquatic relative of the elephant. Manatees can be found in the warm waters of shallow rivers, bays, estuaries and coastal waters. Rarely do individuals venture into waters that are below 68 degrees Fahrenheit. Well known for their gentle, slow-moving nature, manatees have also been known to body surf or barrel roll when playing.

The current main threat to manatees in the United States is being struck with boats or slashed with propellers. Manatees have enjoyed nearly three decades of protection policies that have focused on requiring boats to slow their speed in known manatee habitats ("no wake" zones). Despite this protection, however, manatee deaths from watercraft collisions have continued to rise, peaking at 96 in 2006.

Although manatees are normally very slow swimmers, they are capable of brief bursts of power when frightened. This fact has caused researchers to question why manatees cannot learn to avoid boats, even after repeated injuries. This led to their hypothesis that manatees may be unaware of impending danger because they are unable to effectively hear approaching boats.

Dr. Edmund Gerstein, PhD is one of the leading experts on manatee behavior and is director of marine mammal research at the Charles E. Schmidt College of Science at Florida Atlantic University. His research suggests that the "no wake" zones designed to protect the manatee may be contributing to the increased number of propeller strikes because the animals cannot hear the propellers at idle speeds.

Peak hearing sensitivity for manatees lies between 16-18 kHz. Below 16 kHz, sensitivity decreases approximately 10 dB per octave. Below 2 kHz, hearing sensitivity drops precipitously and the low-frequency cut-off is approximately 400 Hz. The idle speed on boats is often around 600 Hz. These hearing thresholds were tested in quiet, captive pools but the manatee's natural habitat is noisier and therefore manatees' hearing thresholds are even higher in the wild to hear over the masking noise. Also, many of the lower frequency sounds do not propagate far enough to reach the manatees' ears. Typical ambient sound levels of only 70-90 dB SPL can significantly interfere or mask the sound of boats.

Researchers are working on a sound-emitting device that can be placed on the front of a boat. The device incorporates a parametric design to produce multiple frequencies. The different frequencies produced fall within the animal's best range of hearing. The device incorporates higher frequency elements of boat motor noise as a "carrier" signal to provide a sound that "ramps" up or down as the boat changes speed, which manatees can recognize and detect.

In field tests, the manatees are avoiding the alarm without any prior experience. If an animal cannot detect the danger they cannot learn to avoid it. Since speed laws have been enacted, there has been an increase in manatees with multiple boat scars, and the deaths from boat collisions have increased to record highs. In controlled tests, manatees have successfully avoided boat approaches with prototypes of the warning system. Without the warning device, it was necessary to veer away from the animals 97 percent of the time when approached with the same boat at the same speed.

From: Audiology Today Mar/Apr 2009

06 March 2009

Dental Fillings and Hearing Loss

Rothwell and Boyd (2008) evaluated hearing thresholds and amalgam dental fillings across 39 non-smoking women, ages 40 to 45 years. When non-amalgam fillings were used, there was no correlation between fillings and hearing thresholds. However, in those with amalgam fillings, each additional amalgam filling was associated with a 2.4 dB decline in hearing threshold.

Tambs et al (2003)determined that much of age-related hearing loss can be accounted for by noise exposure, ear infections, head injury and gender, yet the remaining portion was possibly due to environmental toxins. Rothwell and Boyd suggest that perhaps the use of amalgam fillings and the well known ototoxic effects of amalgam may be a component of what is typically considered to be age-related hearing loss.

The ongoing trend to use composites and other non-mercury containing dental filling materials is encouraged.

24 February 2009

Tinnitus & Neurostimulation

"...For a long time it was assumed that the cause of tinnitus lay in the auditory organ itself. However, it is now clear that the brain is responsible: overactive parts of the brain in the auditory region emit continuous signals that are the cause of the ‘phantom noise’. This over-activity is usually the result of hearing loss. However, noise (buzzing in the ears after visiting a concert or discotheque), an infection or an operation on the ear, or a jaw or neck problem can also cause the symptoms..."

Link: Tinnitus and the beneficial effects of psychological treatment and neurostimulation