Integrated Development and Maturation of the Hearing System; A Critical Review Article

Abstract

The understanding of development and maturation of the auditory system is essential for many reasons, including the practical aspects of auditory behaviour, testing, and teaching a hearing-impaired child to communicate effectively. The study of maturation of the auditory system is gaining increasing importance also because it should help us to interpret correctly certain aspects of auditory behaviour in infants. When studying the auditory system we should not be concerned solely with development of function in isolation; the emphasis is on integrated development. Understanding a process of integrated development enables us to understand the peculiarities of auditory behaviour in infants. Sound became the raw material of human language for good reasons. It is the only medium which made it possible to transmit efficiently complex information encoded in human language. Phylogenetically, hearing in vertebrates is a late development, and because of this, in certain unfavourable circumstances the hearing system is more vulnerable than other phylogenetically older systems. Within the auditory system, high-frequency hearing is also phylogenetically a late development, and therefore more vulnerable to certain unfavourable metabolic influences. In all species there is a 'best frequency' range, usually the one which is most vital for communication. In humans the best frequency range is the one which is most important for transmitting speech sounds. This is already noticeable in newborn and very young infants, that is, we can obtain the best reactions in the frequencies which are important for speech. Higher sensitivity for perception of patterns is already developed in newborn and young infants (and acquires a special significance). Direction detection and localisation of sound source develops gradually. It is fully developed only when the auditory pathway matures and when the function is well integrated with the maturing motor system. The ears of the young are more vulnerable to noise damage and therefore a variety of protective mechanisms exist. The quality of the sound environment of the infant is important and can be decisive for further development. It is highly desirable to detect hearing impairment as soon as possible after birth. Lack of stimulation of the auditory system, even when it functions only partially, or along a very narrow channel of communication, may lead to permanent complete loss of function of the auditory centre. But this could be prevented by early stimulation, even when it is possible only via the narrow channel of communication which fortunately is present in the great majority of cases of even severely hearing-impaired children.

Addressing the Global Neglect of Childhood Hearing Impairment in Developing Countries

“…Adequate auditory stimulation, in early childhood in particular, is the foundation for optimal speech and language development as well as the acquisition of literacy skills [1,2]. Failure to detect early and effectively manage within the first year of life a permanent hearing impairment that is congenital or that originates in the neonatal period has been associated with significant and irreversible deficits in speech and in linguistic, cognitive, and educational development [3,4].…”

Congenital Nonprofound Bilateral Sensorineural Hearing Loss in Children: Comprehensive Characterization of Auditory Function and Hearing Aid Benefit

“…The median PTT of 50 dB HL at 2000–4000 Hz (as recorded at ≈11 years of age) was similar to the median ABRthr at birth, i.e., 50 dB nHL. This similarity might reflect stable hearing thresholds—on a group level—if the neural maturation, which affects hearing sensitivity [ 13 , 14 ] in a frequency-dependent way at postsynaptic levels [ 73 ], outbalances the acoustical effect of the growth of the outer ear canal [ 12 ].…”

“…They were 9–13 years old at the time of inclusion. The reason for choosing this study group, recruited from [ 11 ], was the well-defined material of consecutively identified SNHLs at birth, no problem with acoustical effects due to growth of the outer ear canal [ 12 ] or neural maturation in a frequency-dependent way [ 13 , 14 ] as in young children, and the opportunity to use advanced psychoacoustical tests and questionnaires.…”

Prenatal and postnatal development of the mammalian ear

“…The vestibular structures are well developed at birth, however they do continue to mature postnatally (Fisch, ). The number of hair cells in all five structures increases from PND0 to PND3 then decreases again from PND3 to PND7, which coincides with ongoing hair cell apoptosis that starts at E19, reaches a peak at PND3 to decrease again around PND7 (Zheng & Gao, 1997).…”