Understanding Audiological Information
This information is part of an online guide, Resources for Mainstream ProgramsAudiology is the science of measuring and describing hearing and hearing loss. If an audiologist is available in your school system, he or she may help you understand a student's hearing abilities and needs. The audiologist is a professional who can interpret hearing test results and will be able to provide guidance for educational and classroom planning.
Most hearing tests are recorded on an audiogram. The audiogram is a graph used to chart hearing thresholds. Thresholds are the quietest levels at which an individual can hear specific frequencies or pitches. While hearing evaluations may look different from each testing facility, the audiogram and the frequencies tested are usually the same.
Most audiograms have a key that explains the symbols and terms used. Here are some terms that you are likely to encounter:
Hertz (Hz)-The terminology used to describe the frequency or pitch of sound. The pitches measured on an audiogram are typically 250 Hz (lowest pitch) through 8,000 Hz (highest pitch). These frequencies are measured because speech contains most of its energy in this range.
Decibel (dB)-The terminology used to describe the intensity or loudness of a sound. Zero dB is usually the quietest sound measured on an audiogram. The loudest sound typically measured is 120 dB.
"O" and "X"-The symbols used to record thresholds on an audiogram. "O" represents the right ear and "X" represents the left ear.
Pure Tone Average (PTA)-The average of the thresholds at 500 Hz, 1,000 Hz; and 2,000 Hz; for each ear. The PTA is often used to describe an individual's degree of hearing loss (see below). For example, when a hearing loss is described as an 80 dB loss, that number probably represents the PTA.
Speech Detection Threshold (SDT) or Speech Awareness Threshold (SAT)-The loudness level at which an individual begins to be aware of speech sounds, without understanding the sounds, words, or phrases used. When individual sounds are used, they are typically those chosen to represent various components of the frequency range often with "oo" and "aa" (low pitch), "ee" (mid-pitch), and "sh" or "s" (high pitch).
Speech Recognition Threshold (SRT)-The quietest level at which a person can understand words. This ability is measured by asking a person to repeat or point to pictures of two syllable words with equal stress placed on both syllables such as hotdog or airplane.
Word Recognition Testing-Usually described by a percentage score or the terms excellent, good, fair, or poor. This test evaluates a person's ability to understand one-syllable words at a comfortable listening level. This test may be done at varying loudness levels, in quiet, or in the presence of background noise. While this test does not determine how well a person will understand speech in a more natural environment, it does help identify whether they have difficulty with certain sounds or in noisy versus quiet environments.
How Loud is Loud?
You may be wondering how loud everyday sounds are and how that compares with an individual student's hearing levels. Here are the decibel or loudness levels of some common sounds:
- 0-25 dB HL: Approximate threshold for normal hearing
- 30 dB HL: Whisper at five feet
- 50 dB HL: Average conversation
- 90-110 dB HL: Loud auto horn, a person nearby who is yelling
- 100-110 dB HL: Motorcycle engine
- 150-170 dB HL: Jet engine (painful for humans)
With noise from cars and trucks, lawn equipment, people, video games, MP3 players, and all the other parts of today's environment, the world is a noisy place. All of that noise can impact hearing. Prolonged exposure to loud sounds (sounds over 80 dB) can cause temporary or permanent damage to hearing. Hearing loss due to noise often does not become noticeable until a person is older. This is why it is important for individuals of all ages, whether they are hearing, hard of hearing, or deaf (with residual hearing), to use earplugs or other hearing protection around loud sounds. For more information, see WISE EARS® at http://www.nidcd.nih.gov/health/hearing/wiseears.asp.
Interpreting the Audiogram
Speech understanding is related to how many parts of the listening "puzzle" are available for someone to make sense of words, phrases, or sentences. The more parts that a person can hear, the easier it is to understand what is heard. Some sounds are more important than others for speech understanding. In general, consonants provide more information and are therefore more important for speech understanding than vowels. For example, "SP_C__L" is easier to understand than "__E_IA_."
Speech sounds have energy in different parts of the frequency range. For example, vowels have most of their energy in the low pitches, while many consonants have energy in the higher pitches. If a person has the pattern of hearing loss where he or she can only hear lower-pitched vowels and few consonants, he or she may have great difficulty understanding words. The more access an individual has to hear the consonant sounds in the higher pitches, the greater his or her potential to acquire and understand spoken language.
For some people, word understanding increases significantly when they have access to information from looking at the lips, face, and other body language cues. This is called speechreading. Sounds that are typically hard to hear may be more readily visible on the lips. For example, the "f" sound in leaf is difficult to hear because it is a high pitched, quiet sound, but it is easy to see on the lips. The combination of hearing some parts of a word and seeing complementary parts on the lips and face sometimes fills in the parts of the puzzle and promotes speech understanding for some people.
Speechreading is not easy. To better understand, have someone mouth the words bat, pat, and mat without using their voice. Can you tell the difference? Probably not since the words look the same. Speechreading may improve with practice, but not everyone is good at it.
Resources: Understanding Audiological Information
American Speech-Language-Hearing Association: Hearing loss. http://asha.org/public/hearing/disorders/default.htm
DeConde Johnson, C., Benson, P. V., & Seaton, J. B. (1997). Educational audiology handbook. San Diego: Singular Publishing Group. Mahshie, J., Moseley, M. J., Scott, S., & Lee, J. (2006).