One can wonder what incidence the onset time of deafness might have.
To quote Prof. J.C. LAFON:
« The exact timing of the onset of deafness is crucial for the prognosis. The impact of perceptive deafness varies according to the stage it occurs at:
a. The normal development of the auditory neurological structures and associative pathways, which begins in utero and is completed at the age of 2 years.
b. The acquisition of the acoustic representation of the environment, which occursbetween birth and the age of 3 years.
c. The elaboration of vocal communication, for both signalling and answering, which starts at 3 months until the age of 2.
d. The emerging control of phonation and the elaboration of verbal communication – combining both the verbal thought and the verbal speech – which develop, based on family and social environments, between the ages of 1 year and 5 years old.
e. The organisation of social relationship through speech – both heard and spoken – which is in constant evolution throughout life.» (1)
Prof. J.C. LAFON then provides further information on the incidence of deafness:
«deafness diagnosis should be sought at the very first sign, direct or indirect, of a perception impairment.
a. For an existing deafness, or a deafness that occurred at birth (congenital deafness), it is mandatory to have established a clear diagnosis and to have provided appropriate prosthetic devices by the age of 12 months in case of profound deafness, by the age of 24 months in case of severe deafness and by the age of 36 months in case of moderate deafness.
The diagnosis, hearing aids devices fitting and educational monitoring often take over a year to be completed. Making a diagnostic may be complicated, all the more so when deafness is moderate and combined to other impairments.
As a result, detection of the impairment has to be performed before the age of 3 months in case of profound deafness, before the age of 1 year in case of severe deafness and before the age of 2 years in case of moderate deafness.
b. As far as acquired deafness is concerned, the diagnosis should be made at the onset of deafness and medical care should be organised immediately, no matter the age of the child. Perceptive deafness is irreversible. It requires additional care, where hearing devices are combined to psychological monitoring and a thorough speech therapy.» (2)
(1) Professor J.C. LAFON « la surdité de l’enfant, dépistage et prévention » («Childhood deafness, diagnosis and prevention») pp. 27-28 – this document is part of « les techniques éducatives et thérapeutiques de handicap chez l’enfant et l’adolescent » presented at the ‘Séminaire de Formation de l’ENSP’ meeting in RENNES, France, 1989.
(2) Professor J.C. LAFON « la surdité de l’enfant, dépistage et prévention » («Childhood deafness, diagnosis and prevention») pp. 28-29 – this document is part of « les techniques éducatives et thérapeutiques de handicap chez l’enfant et l’adolescent » presented at the ‘Séminaire de Formation de l’ENSP’ meeting in RENNES, France, 1989