The semantic network structure is a core aspect of the mental lexicon and is, therefore, a key to understanding language development processes. This study investigated the structure of the semantic network of adolescents with intellectual disability (ID) and children with typical development (TD) using network analysis. The semantic networks of the participants (nID = 66; nTD = 49) were estimated from the semantic verbal fluency task with the pathfinder method. The groups were matched on the number of produced words. The average shortest path length (ASPL), the clustering coefficient (CC), and the network’s modularity (Q) of the two groups were compared. A significantly smaller ASPL and Q and a significantly higher CC were found for the adolescents with ID in comparison with the children with TD. Reasons for this might be differences in the language environment and differences in cognitive skills. The quality and quantity of the language input might differ for adolescents with ID due to differences in school curricula and because persons with ID tend to engage in different out-of-school activities compared to TD peers. Future studies should investigate the influence of different language environments on the language development of persons with ID

When children start formal education, they are expected to be able to express complex thoughts. However, in order to do so, they need to be able to use both complex grammatical structures and a variety of words. One group that is at risk of having a delay in terms of their expressive language ability is children with cochlear implants (CI). In this study, we evaluated whether children with CI perform comparably to children with typical hearing (TH) on a standard expressive spoken grammar and a standard expressive spoken vocabulary task when the groups were matched on non-verbal intelligence and working memory capacity. It was found that the children with CI in this study performed more poorly on a standard expressive spoken vocabulary task but not on a standard expressive spoken grammar task when compared to the children with TH. Differences in terms of expressive spoken vocabulary do not seem to be explained by differences in cognitive ability. In addition, the variation in terms of expressive spoken language ability was larger in the children with CI compared to the children with TH. This might be explained by additional confounding factors, like the time of language deprivation or by a greater influence of cognitive differences for the acquisition of spoken language for children with CI.

The usage-based model of language acquisition assumes that language is learned by its usage. General cognitive processes, especially analogical reasoning ability, are assumed to lead to the understanding of words and grammatical structures. It has been argued that the time of language or auditory deprivation children with cochlear implants (CIs) often experience early in life, might affect both their language and their cognitive abilities. Children with CIs have disadvantages in terms of language acquisition as they start receiving language input later than peers with typical hearing (TH), and the perceptual quality of the input is reduced. However, they might have additional difficulties in language acquisition if their analogical reasoning ability is negatively influenced by the language or auditory deprivation early in life. The results found in this thesis show that the language delays often seen in children with CIs are not explained by differences in analogical reasoning ability. Results indicate that analogical reasoning ability has a limited influence on language acquisition for the tested age-group. However, language abilities affect the performance on analogical reasoning tasks which are either verbal or can be supported by verbal strategies. This needs to be taken into consideration when comparing analogical reasoning ability of children with CI sand children with TH. In addition, the results from this thesis indicate that the structure of the mental lexicon is associated with the communication skills of children with CIs. The structure of the mental lexicon is most likely influenced by the amount of language input a child receives. The main implication of the results is that emphasis should be put on reducing the duration of language deprivation and to improve the quality of the language input for children with CIs.