Hemispheric asymmetries in bilinguals: tongue similarity affects lateralization of second language.

It is known that the left hemisphere of the human brain is critical in understanding and producing spoken language, but it remains a topic of great interest determining the cerebral lateralization of multiple languages. The aim of this study is to examine the effects of similarity between languages on hemispheric asymmetry of bilingual brains. The involvement degree of left and right hemisphere was examined during the processing of the first (L1) and second (L2) language in two different groups of bilinguals with English as L2. The first group consisted of German native speakers and the second group of Italian native speakers. Subjects from the two groups acquired L2 later in life (after the age of six) and had a comparable level of proficiency in second language comprehension. The functional lateralization was tested by a classical dichotic test with words in L1 and L2. Dependent variables were number of responses associated to words presented at the left vs. right ear and reaction time. Results showed a significant right ear advantage (REA) for number of responses in both languages and in both groups. However, the REA for L2 (English) processing was stronger in the German group. Reaction times were significantly lower during L1 processing and showed a trend towards the results obtained with the number of response variable. This study provides neuropsychological evidence pointing to a different lateralization pattern in the elaboration of a same L2 if L1 comes from different linguistic roots.