–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Language is a uniquely human capacity. Members of other species communicate, but those communications are neither as complex nor as interactional as human language. In spite of its greater complexity, however, human language evolved within the constraints of the mammalian auditory system, a system shared by all mammals. For individual children, spoken language must develop within the constraints of their own auditory systems. But even though the great majority of children can hear sounds at birth, there is a tremendous amount of development in the auditory system that takes place after birth, extending through puberty. This development happens in the central auditory pathways, which means the ability to perform more complex functions on acoustic signals does not reach maturity until near puberty. Thus, a reasonable proposal is that any condition that delays the development of the child’s auditory system can disrupt language development, especially for aspects of language most dependent upon having sophisticated auditory functions. This proposal was explored in this study. Furthermore, the idea was explored that two conditions heretofore known to negatively affect language development may exert some of that influence by disturbing the normal timing of auditory development. These conditions are poverty and premature birth.
Developmental scientists have long searched for the roots of the delays in language acquisition exhibited by children living in poverty. That work has focused on language models in the child’s environment, which are fewer in quantity and poorer in quality than what a middle-class child hears. But even though this factor has been found to explain effects of poverty on child language abilities to some extent, those relationships are never found to be very strong. This means that some other factor(s) must also be contributing.
Children born prematurely are known to have delayed language development, and the usual explanation is that the auditory environment in the neonatal intensive care unit is at once too noisy and too void of the human voice, which is available in utero. Again, those explanations might explain some of the deficit, but animal studies show that the simple act of being removed from the womb before full gestation leads to neurodevelopmental challenges. Obviously, those challenges for animals do not include language acquisition, but for human children born too early, language acquisition can be a challenge.
Our primary findings are:
Relatively strong relationships exist between measures of auditory function and language measures, and these relationships were strongest for the most complex language skills.
Socioeconomic status and gestational age at birth were related to measures of both auditory and language development.
Effects on language development of both socioeconomic status and gestational age at birth could be explained by their effects on auditory function, to at least some extent.
These results mean that developmental delays in the biological structures and functions underlying language disorders are happening long before the language problem can be diagnosed. We need to provide intensive interventions right from birth focused not only on discrete language targets, but on the whole child.
Archie’s Cochlear Implant Laboratory, The Hospital for Sick Children, University of Toronto, The Hospital for Sick Children, TORONTO, ON, M5G1X8, Canada
Popular version of 3aPP5 – Non-auditory processing of cochlear implant stimulation after unilateral auditory deprivation in children
Presented at the 184 ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0018669/
Decades of research have shown that hearing from only one ear in childhood should not be dismissed as a “minimal” hearing problem as it can impair language, cognitive, and academic development. We have been exploring whether there are effects of unilateral hearing on the developing brain. A series of studies has been done in children who have one deaf ear and who hear from the other side through a normal or typically hearing ear, a hearing aid, or a cochlear implant. We record electrical fields of brain activity from electrodes placed on the surface of the head (encephalography); we then calculate what parts of the brain are responding.
The findings show that auditory pathways from the hearing ear to the auditory cortices are strengthened in children with long term unilateral hearing. In other words, the hearing brain has developed a preference for the hearing ear. As shown in Figure 1, responses from the better hearing ear were also from areas of the brain involving attention and other sensory processing. This means that areas beyond the auditory parts of the brain are involved in hearing from the better ear.
Figure 1 legend: Cortical areas abnormally active from the experienced ear in children with long periods of unilateral cochlear implant use include left frontal cortex and precuneus.Adapted from Jiwani S, Papsin BC, Gordon KA. Early unilateral cochlear implantation promotes mature cortical asymmetries in adolescents who are deaf. Hum Brain Mapp. 2016 Jan;37(1):135-52. doi: 10.1002/hbm.23019. Epub 2015 Oct 12. PMID: 26456629; PMCID: PMC6867517.
We also asked whether there were brain changes from the ear deprived of sound in children. This question was addressed by measuring cortical responses in three cohorts of children with unilateral hearing who received a cochlear implant in their deaf ear (single sided deafness, bilateral hearing aid users with asymmetric hearing loss, and unilateral cochlear implant users). Many of these children showed atypical responses from the cochlear implant with unusually strong responses from the brain on the same side of the deaf implanted ear. As shown in Figure 2, this unusual response was most clear in children who had not heard from that ear for several years (Figure 2A) and was already present during the first year of bilateral implant use (Figure 2B).
Figure 2 legend: Cortical responses evoked by the second cochlear implant (CI-2) in children receiving bilateral devices. A) Whereas expected contralateral lateralization of activity is evoked in children with short periods of unilateral deprivation/short delays to bilateral implantation, abnormal ipsilateral responses are found in children with long periods of unilateral deprivation despite several years of bilateral CI use. Adapted from: Gordon KA, Wong DD, Papsin BC. Bilateral input protects the cortex from unilaterally-driven reorganization in children who are deaf. Brain. 2013 May;136(Pt 5):1609-25. doi: 10.1093/brain/awt052. Epub 2013 Apr 9. PMID: 23576127. B) Abnormal ipsilateral responses are also found throughout the first year of bilateral CI use in children with long periods of unilateral deprivation/long delays to bilateral CI. Adapted from Anderson CA, Cushing SL, Papsin BC, Gordon KA. Cortical imbalance following delayed restoration of bilateral hearing in deaf adolescents. Hum Brain Mapp. 2022 Aug 15;43(12):3662-3679. doi: 10.1002/hbm.25875. Epub 2022 Apr 15. PMID: 35429083; PMCID: PMC9294307
New analyses have shown that this this response from the CI in the longer deaf ear includes areas of the brain involved in attention, language, and vision.
Results across these studies demonstrate brain changes that occur in children with unilateral hearing/deprivation. Some of these changes happen in the auditory system but others involve other brain areas and suggest that multiple parts of the brain are working when children listen with their cochlear implants.
Language is a uniquely human capacity. Members of other species communicate, but those communications are neither as complex nor as interactional as human language. In spite of its greater complexity, however, human language evolved within the constraints of the mammalian auditory system, a system shared by all mammals. For individual children, spoken language must develop within the constraints of their own auditory systems. But even though the great majority of children can hear sounds at birth, there is a tremendous amount of development in the auditory system that takes place after birth, extending through puberty. This development happens in the central auditory pathways, which means the ability to perform more complex functions on acoustic signals does not reach maturity until near puberty. Thus, a reasonable proposal is that any condition that delays the development of the child’s auditory system can disrupt language development, especially for aspects of language most dependent upon having sophisticated auditory functions. This proposal was explored in this study. Furthermore, the idea was explored that two conditions heretofore known to negatively affect language development may exert some of that influence by disturbing the normal timing of auditory development. These conditions are poverty and premature birth.
