Our speech and language normally develops rapidly during the first few years of life. This depends critically on our ability to hear. The aim of this section is to learn the basic temporal sequence of events in language acquisition and to the consequences of profound hearing loss on this process.
At the end of this unit, each student should be able to:
1. State the role of the auditory system in acquisition of speech and language behavior.
2. Describe the normal sequence of development of language during the first 4 years of life.
By the 30th week of intra-uterine life, the peripheral auditory structures are nearly completely developed and the fetus is responsive to loud sounds. These responses take the forms of fetal movement and changes in heart rate. During the neonatal period, there continues to be major structural changes in the auditory pathways, from the auditory nerve to the cerebral cortex. These changes continue long into childhood. The newborn child responds to various aspects of the acoustic world and the responses are diversified. Later the infant becomes even more aware of the acoustic environment and responds to it in more appropriate ways. Thus, one may identify quieting, localizing, and attending in response to a sound.
Auditory behaviors that are prerequisite to speech and language development include:
Attention - the ability to consciously focus on the sound and its source.
Figure-ground relationship - the ability to focus on and distinguish certain sounds in an environment filled with sound.
Discrimination - the ability to tell the difference between sounds.
Temporal ordering - the ability to distinguish the time-sequencing of sounds (e.g. human speech).
Storage - the ability to retain information about sounds heard.
Association - the ability to connect a sound with its physical reality.
In addition, there are certain linguistic constructs that are related to communication behavior that must also be learned by the child. These include learning the elements and rules for combining sound elements, learning the vocabulary (lexicon) of the language, learning ways in which words are assembled to produce grammatically correct sequences, and learning the meaning of words as a function of the context within which they are used.
Children with normal hearing develop speech and language in predictable stages. While there may be variation in the times of onset, and length of time of each of these stages, they are always present. Should this pattern not develop normally, the child may face a lifelong communication handicap. Normal hearing is crucial for this development and thus deviation from this pattern of development is often a sign that the child has a hearing loss.
During the first year
0-1 month (newborn stage): Reflexive behavior, suck-swallow patterns, nondifferentiated crying, vegetative sounds
2-3 months (cooing stage): Definite stop and start to oral movement
4-6 months (babbling): Greater independent control of tongue, prolonged strings of sounds, experiments with sounds, sound play (da, ma, di, du.....).
6-10 months (reduplication babbling): Repetetive syllable production, increased lip control, incompletely formed plosives (p,b,t,d) and nasals.
11-14 months (first words, usually nouns): elevates tongue tip, complex babbling, intonational patterns.
After the first year
18 months: Vocabulary of 20-100 words including nouns and verbs and other parts of speech. Single word sentences.
24 months: Vocabulary has grown to 200-300 words, including nouns, verbs and other parts of speech. Two words sentences.
36 months: Vocabulary has grown to 900 words including nouns, verbs, pronouns and adjectives. Three word sentences. About 90% of the childs speech is intelligible.
48 months: Vocabulary is now at about 1500 words.
Hearing impairments in children may, as in adults, be of peripheral or central origin. If peripheral, they may be conductive or sensorineural in nature. The severity of loss may range from mild to profound. The development of language depends on the age of onset of hearing loss. Those children born with a hearing loss will have a much more severe communication handicap that a child whose hearing loss occurred after language acquisition. Similarly, the adult whose hearing is suddenly lost (e.g. by ototoxicity) will not suffer the same handicap as the child whose language abilities are not fully developed.
Pre-lingual hearing loss has a profound effect on acquisition of language. Hearing loss that occurs in children or adults after language has developed results in a loss or deterioration in language performance. This shows up in the following ways:
Articulation: this is characterized by nasal emission of sound, confusion over voiced and voiceless sound, substitution of consonants, omission of consonant clusters, increasing duration of sound.
Voice: this is characterized by hypernasality, monopitch, and monoloudness
Language: this is characterized by dropping of certain grammatical classes of words (e.g. articles, prepositions, conjunctions), changing of certain inflectional endings (e.g. dropping the possessive or plural "s"), dropping the past tense "t" or "d", using less complex sentence construction, reducing the overall amount of language behavior.
[NEXT]Objective 1: Role of the Auditory System in Acquisition of Speech and Language Behavior
Objective 2: Chronology of speech and language acquisition
Objective 3: Communication disorders related to auditory impairment