Speech Development
Speech development is so closely related to degree of hearing loss so the greater the loss, the more difficult it tends to be to develop clear speech. There are many sounds in our world that occur below the "0" established as the baseline for normal hearing on the audiogram, but these generally do not fall within the range of the human ear. The potential for confusion between consonants occur dramatically with a sloping audiogram. Each sound is a burst of energy or a speech sound (phoneme) that occurs a specific frequencies. Hearing losses do not usually occur as a flat overall decrease in the level of sounds but as decreases in frequencies. When a high frequency loss occurs, lower frequencies may still be within the normal range. As a result, some of the information which occurs in the compromised frequencies and which distinguishes one sound from another can be lost causing different phonemes to sound similar therefore making words difficult to understand. The person with normal hearing, hears all 16 consonants as different sounds. When a hearing loss occurs in the higher frequencies, 5000Hz and above, /k/ and /p/ begin to sound the same. At 2500 Hz the /t/ can also be confused with the /p/ and /k/. By the time the loss begins at 300 Hz sharply sloping to profound by 4000 Hz, only 3 distinct consonants are heard:
/t/, /k/, /p/, /f/, /th (voiceless)/, /s/, /sh/, sound the same
/m/ or /n/ sound the same
/d/, /g/, /b/, /v/, /th (voiced)/, /z/, /zh/ sound the same
Consonants are pitched at a higher frequency than vowels so lie to the right of the audiogram. They are spoken more softly, so occur closer to the top of the chart. They also carry more important word information and are more important for speech intelligibility. With background noise added to make listening more difficult, the difficult becomes barely possible and often impossible. Consonants separate words into syllables and from each other. When these barriers are blurred or missing, then the words start to run together making speech incomprehensible.
Figure 2-4: Relationship of Degree of Long-Term Hearing Loss and Understanding of Speech/Language
Degree of Hearing Loss Based on Pure Tone Average (500-4000 Hz) |
Possible Affects of Hearing Loss on the Understanding of Speech/Language |
|---|---|
Normal Hearing -10 to +15dB HL |
Children with hearing sensitivity in this range will detect the complete speech signal even at soft conversation levels. However, good hearing does not guarantee a good ability to discriminate speech in the presence of background noise. |
Minimal (Borderline) 16 to 25dB HL |
May have difficulty hearing faint or distant speech. With a 15 dB loss, a student can miss up to 10% of speech signals when the teacher is at a distance greater than 1 meter or if the classroom is noisy. |
Mild 26 – 40 dB HL |
With a 30 dB loss, a student can miss 25-40% of speech. The degree of difficulty experienced in school will depend upon the noise level and acoustic design in the classroom and distance from a teacher. It can also be affected by which speech sounds are heard clearly. Without amplification a child with a 35 to 40 dB loss may miss at least 50% of class discussions, especially when voices are faint or teachers are not in the line of vision. This child will miss consonants especially with a high frequency loss. |
Moderate 41 to55 dB HL |
Understanding conversational speech at a distance of 1 to 1 ½ meters (face to face) only if structure and vocabulary are controlled. Without amplification, the amount of speech signal missed can be 50 to 75% with a 40 dB loss and 80 to 100% with a 50 dB loss. A student is likely to have a delayed or defective syntax,vocabulary, speech problems and an unnatural voice quality. |
Moderate-Severe 56 to 70 dB HL |
Without amplification, conversation must be very loud to be understood. A 56 dB loss can cause a child to miss up to 100% of speech information. This child will have marked difficulty in school situations requiring verbal communication in both one-to-one and group situations, delayed language, and syntax, reduced speech intelligibility and atonal voice quality. |
Severe 71 to 90 dB HL |
Without amplification a child may hear, but not necessarily understand loud voices at about 1 step away from the ear. When amplified optimally, children with up to a 90 dB loss should be able to identify environmental sounds and identify all the speech sounds. If onset of the hearing loss is prelingual, oral language and speech may not develop spontaneously or will be severely delayed. If the hearing loss is of a later onset, speech is likely to deteriorate with voice quality becoming atonal. |
Profound Greater than 90 dB HL |
This child is aware of vibrations more than intonation. Many rely on vision rather than hearing as primary avenues for communication and learning. Detection of speech sounds will be difficult. It will also depend on the individual's use of residual hearing and amplification. Speech and oral language will not develop spontaneously. With a later onset, speech and language will deteriorate rapidly. |
Unilateral One normal ear and one ear with a permanent hearing loss. |
This child may have difficulty hearing faint or distant speech; usually has difficulty localizing sounds and voices; and will have greater difficulty understanding speech when the environment is noisy and/or reverberant. Will have difficulty hearing and understanding soft speech from the side with the loss, especially in a group discussion. Speech and language can be affected if the good ear is subject to frequent conductive hearing losses. |
Adapted from: Bernero, R.J. & Bothwell, H. (1966). Relationships of hearing impairment to educational needs. Illinois Department of Public Health and Office of the Superintendent of Public Instruction. Unit II: Language and Deafness