Language and its interacting components: the right hemisphere hypothesis in derivational morphology.

Traditionally, it has been assumed that language is part of a distributed neural system largely lateralized to the left cerebral hemisphere. However, more recent studies have challenged the traditional hypothesis supporting a more interactive view of language processing. Instead of considering the language faculty as modular and independent from other cognitive functions, it is hypothesized that language makes use of other cognitive domains. This issue has also been specifically addressed in derivational morphology processing, a language task traditionally considered purely linguistic. Very recently, in a group of Italian non-aphasic right brain-damaged (RBD) subjects, a selective deficit in deriving nouns from verbs (e.g. osservare [to observe] --> osservazione [observation]) was reported. It was attributed to damage to response selection and inhibition mechanisms required by the derivational task. The aim of the present study was to investigate this issue further. Twelve RBD subjects, six of whom were selectively impaired in deriving nouns from verbs, and six healthy controls were asked to perform a response selection task that required the activation of facilitatory and inhibitory components. Results showed that subjects with a derivational morphological deficit exhibited slower reaction times than the subjects in the other RBD group only when they had to inhibit the expected response to select the correct answer. Moreover, lesion analysis revealed the involvement of the right subcortical structures. The relationship between derivational morphology and response selection mechanisms in the right hemisphere is discussed within the view of inter-hemispheric cooperation between different cognitive domains in language tasks.