Recently,Recently, I’veI’ve been trying to orga- evaluations, and they are truly im- nize some of the columns and articles pressive, the information and insights RI’veI’ve written overover the past ten years.years. provided by the simple audiogram As I was looking through them, it be- can still provide the most pertinent came apparent that I’ve neglected to information to explain the behavioral discuss what is perhaps the implications of a hearing loss. most important hearing di- Perhaps the most important in- mension of all, the simple sight of all is an appreciation of how The audiogram. specifi c audiograms impact upon the In reality, however, perception of certain speech sounds. the “simple” audiogram, Without including speech in the Audiogram: and particularly its im- equation, it is simply not possible to Audiogram: plications, is not quite so intelligibly discuss the audiogram. simple. Even though just This, after all, is the signal we are about everybody who re- most interested in hearing (not to Explanation ceives a hearing aid has his minimize the specifi c needs of certain or her hearing tested with groups of people for other types of a pure-tone audiometer, sounds, such as musicians). and not everybody receives a comprehensive explanation Figure One Audiogram — of exactly what the results The “Speech Banana” Signifi cance mean and what the impli- cations are for them. The audiogram of a fairly typical And even for those who audiogram can be seen in Figure 1. do, at a time when prospec- (My thanks to Brad Ingrao for creat- By Mark Ross tive hearing aid purchasers ing these fi gures for me.) Let’s fi rst go are being inundated with through the fundamentals. Frequency new information, anxious (or pitch) is depicted on the horizon- about the test results, and worried tal axis, from low frequencies on the about the cost involved, much of this left (250 Hz) to high frequencies on The information and explanation will be forgotten or mis- the right (8,000 Hz). For some spe- construed by the time several weeks cifi c purposes, it may be useful to test insights provided by the have passed. I know that I’m often be- 125 Hz as well as some frequencies simple audiogram can still mused when I hear what some people higher than 8,000 Hz (for example, a recount to me what they think their progressive hearing loss above 8,000 provide the most pertinent audiologist told them about their Hz can occur with certain type of oto- information to explain the audiogram and its implications. I’m toxic medications). sure this was not what they were told, The amount of hearing loss is shown behavioral implications of but it is what they remember. And in on the vertical axis with the higher a hearing loss. Here is a this context, that is the only relevant numbers indicating a greater degree consideration. of hearing loss. A symbol on this axis clear explanation of how to For audiologists, the audiogram (red circle for the right ear and blue understand your audiogram. is such a basic dimension and so cross for the left) is a measure of the self-evident that its explanation, person’s hearing threshold at this fre- after the thousandth time, is often quency; i.e., the loudness (intensity) unconsciously truncated and simpli- point where sound is just audible. fi ed. They may go through it by rote Thresholds from zero to 15 dB are memory, unaware that their client considered to be within the normal simply isn’t getting it. For people who hearing range. After that point, people may not even have heard of a pure- will usually begin to display some tone audiometer before they stepped communication diffi culties because of into the audiologist’s offi ce, this is a the elevated hearing thresholds. The quite understandable. To expect them higher the number, the greater the im- to fully understand how the pattern of pact of the hearing loss (referring only their hearing loss impacts upon their to the unaided condition). listening behavior is not very realistic. The 100 dB point should not be Yet, in spite of the recent advances confused with a 100 percent hearing made in diagnostic audiological loss, that is a total lack of hearing. May/June 2004 29 Hearing sensations do continue past ceding and following consonants, are this point, with some audiometers actually secondary cues that can be extending this vertical range to 120 dB. helpful for understanding speech. In short, the audiogram is a chart of Indeed, the ability to take advan- a person’s hearing loss, frequency by tage of these cues may help explain frequency. why some people seem to understand Now note the shaded area extending speech much better than one would across the audiogram (the so-called predict on the basis of their audio- “speech banana”). This is a general, but gram. Still, there are certain anchor static, representation of the acoustical locations for all speech sounds, as speech energy across frequency. Some displayed on the speech banana, and speech sounds, such as vowels, are these can offer valuable insights in predominantly composed of low fre- understanding the effects of differing quency energy, with less of their power hearing losses. Figure One Audiogram: in the higher frequencies. Other speech Looking at the audiogram again, The “Speech Banana” sounds, in particular the voiceless con- and relating it to the speech banana, A fairly typical audiometric pattern sonants, are the reverse. They have most it is apparent that a person with this for older people. of their energy in the high frequencies hearing loss will hear more of the and less in the lower frequencies. lower frequency speech sounds than Only the shaded area of the speech the higher ones. Indeed, some of the banana above the threshold curve is au- higher frequency sounds, such as the dible; portions below will not be per- /s/ sound (the most frequently used ceived. In spite of portrayals to the con- phoneme in the English language) trary on some charts, no speech sound will barely be heard at all. Will this can be pinpointed to a specifi c point person be able to understand normal on the audiogram; all of them spread speech without a hearing aid? Yes, but their energy somewhat along some seg- only with some diffi culty and then ment of the frequency spectrum. only if the talker is close by and raises In addition to their energy locations his or her voice slightly. on the frequency axis, speech sounds There are, unfortunately, many also vary in intensity. Some are natu- people with audiograms similar to this rally weaker (like the voiceless /th/ who do not, for one reason or another, sound, the weakest sound in the Eng- wear hearing aids. One often sees this Figure 2 Audiogram: lish language) and some are naturally type of audiogram in older people The “Ski Slope” more intense (like the vowel /aw/, the whose hearing loss just “crept up” on A severe-to-profound high-frequency strongest). When these are spoken them and who are still not fully aware hearing loss (“ski-slope” curve). in a normal fashion, as in the word of the diffi culty they are causing them- “thaw” there is a 30 dB intensity range selves, their family and friends. between the two phonemes. The in- Conversing with such individuals tensity of all other speech sounds in is a strain on everyone’s part. Often, the English language fall within these they’ll complain that they can “hear” bounds (note, however, that this does the talker but cannot “understand” not take into consideration infl ected what is being said. This is, indeed, a speech, which will move the entire very frequent complaint. Looking at speech banana up and down). the audiogram, we can understand As already noted, the speech ba- somewhat why this should occur: nana is a static representation of they are not hearing the full range of speech sounds. In reality, however, high frequencies where many of the conversational speech is a dynamic consonants have their predominant and time-varying event, with one energy. And we know from many speech sound (phoneme) following years of research, that consonants another in a rapid succession. contribute more to the understand- Figure 3 Audiogram: The specifi c acoustical composition ing of speech than vowels. Without Behavioral Implications of speech sounds is partially shaped a hearing aid, this person would of Hearing Loss by the preceding and following be hearing primarily low frequency Two very different ears sounds in an utterance. These specifi c vowels energy and some part of the with the same pure-tone average. effects, such as the unique modifi ca- voiced consonants, but little or no tions in vowels made by different pre- portions of the crucial voiceless con- 30 Hearing Loss sonant sounds (such as /s/, /t/, and Figure 2 Audiogram — aid (and even with one) this person /k/) . The “Ski Slope” needs to depend upon visual cues I don’t want to give the impression (speechreading) to supplement the that the perception of vowels is unim- This audiogram in Figure 2 is often information received through hearing. portant — on the contrary, it is and described as a “ski-slope” hearing Some people, because of their superior can be very important — only that by loss. Somebody with this type of hear- ability to utilize some of the second- not actually hearing some of the con- ing loss actually hears better at 250 ary cues in a speech signal referred sonants, people with hearing loss have Hz than the one whose audiogram is to above, or their superior linguistic to struggle to fi ll in the acoustical gaps shown in Figure 1, but much worse at ability, may do better than these com- they produce in the stream of speech.