Speech delay caused by congenital deafness, whether peripheral (loss of pure-tone acuity) or central (pure-tone threshold normal by audiogram), is a most important condition but may at first be difficult to discern. One suspects that faulty hearing is causal when there is a history of familial deaf mutism, congenital rubella, erythroblastosis fetalis, meningitis, chronic bilateral ear infections, or the administration of ototoxic drugs to the pregnant mother or newborn infant—the well-known antecedents of deafness. It is estimated that approximately 3 million American children have hearing defects; 0.1 percent of the school population are deaf and 1.5 percent are hard of hearing. The parents’ attention may be drawn to a defect in hearing when the infant fails to heed loud noises, to turn the eyes to sound sources outside the immediate visual fields, and to react to music; but in other instances, it is the delay in speaking that calls attention to it.
As already mentioned, the deaf child makes the transition from crying to cooing and babbling at the usual age of 3 to 5 months. After the sixth month, however, the child becomes much quieter, and the usual repertoire of babbling sounds becomes stereotyped and unchanging, though still uttered with pleasant voice. A more conspicuous failure comes somewhat later, when babbling fails to give way to word formation. Should deafness develop within the first few years of life, the child gradually loses such speech as had been acquired but can be retaught by the lipreading method. Speech, however, is harsh, poorly modulated, and unpleasant, and accompanied by many peculiar squeals and snorting or grunting noises. Social and other acquisitions appear at the expected times in the congenitally deaf child, unlike in the developmentally delayed child. The deaf child seems eager to communicate and makes known all his needs by gesture or pantomime, often very cleverly. The deaf child may attract attention by vivid facial expressions, motions of the lips, nodding, or head shaking. The Leiter performance scale, which makes no use of sounds, will show that intelligence is normal. Deafness can be demonstrated at an early age by careful observation of the child’s responses to sounds and by free-field audiometry, but the full range of hearing cannot be accurately tested before the age of 3 or 4 years. Recording of brainstem auditory evoked potentials and testing of the labyrinths, which are frequently unresponsive in deaf mutes, may be helpful. Early diagnosis is important so as to fit the child with a hearing aid and to begin appropriate language training.
In contrast to the child in whom deafness is the only abnormality, the developmentally delayed child generally talks little but may display a rich personality. Autistic children may also be mute; if they speak, echolalia is prominent and the personal “I” is avoided. Blind children of normal intelligence tend to speak slowly and fail to acquire imitative gestures.
This disorder, also called developmental receptive dysphasia, verbal auditory agnosia, or central deafness, is rare and may be difficult to distinguish from peripheral deafness. Usually the parents have noted that the word-deaf child responds to loud noises and music, but obviously this does not ensure perfect hearing, particularly for high tones. The word-deaf child does not understand what is said, and delay and distortion of speech are evident.
Presumably, the receptive auditory elements of the dominant temporal cortex fail to discriminate the complex acoustic patterns of words and to associate them with visual images of people and objects. Despite intact pure-tone hearing, the child does not seem to hear word patterns properly and fails to reproduce them in natural speech. In other ways the child may be bright, but more often this auditory imperception of words is associated with hyperactivity, inattentiveness, bizarre behavior, or other perceptual defects incident to focal brain damage, particularly of the temporal lobes. Word-deaf children may chatter incessantly and often adopt a language of their own design, which the parents come to understand. This peculiar type of speech is known as idioglossia. It is also observed in children with marked articulatory defects.