Mandarin and English single word processing studied with functional magnetic resonance imaging

Abstract

The cortical organization of language in bilinguals remains disputed. We studied 24 right-handed fluent bilinguals: 15 exposed to both Mandarin and English before the age of 6 years; and nine exposed to Mandarin in early childhood but English only after the age of 12 years. Blood oxygen level-dependent contrast functional magnetic resonance imaging was performed while subjects performed cued word generation in each language. Fixation was the control task. In both languages, activations were present in the prefrontal, temporal, and parietal regions, and the supplementary motor area. Activations in the prefrontal region were compared by (1) locating peak activations and (2) counting the number of voxels that exceeded a statistical threshold. Although there were differences in the magnitude of activation between the pair of languages, no subject showed significant differences in peak-location or hemispheric asymmetry of activations in the prefrontal language areas. Early and late bilinguals showed a similar pattern of overlapping activations. There are no significant differences in the cortical areas activated for both Mandarin and English at the single word level, irrespective of age of acquisition of either language.

Fig. 1.

The top shows the block timing of stimulus presentation. E, English; M, Mandarin. Stimuli were presented every 2 sec. The exposure duration was 1 sec in experiment set 1 and 1.5 sec in set 2. Thebottom shows exemplars of the stimuli and possible responses.

Fig. 2.

Maps in Talairach space show activations associated with the English and Mandarin word completion tasks compared with fixation. Data from representative early (A) and late (B) bilingual subjects are shown. The subject’s left hemisphere is on the right of each image. The top two panels in each sequence show activations above a Z-score threshold of 5 in red and those above 10 in yellow. In the bottom panel, activations above a Z-score threshold of 5 areblue for English and yellow for Mandarin. Where there is overlap of activations, the mapped area is represented in green. The numbers below the images represent distance from the anterior commissural plane in the superior–inferior direction.

Fig. 3.

Activation maps from two representative subjects show basal temporal (BA 37), and midtemporal and posterior temporal (BA 21/22) activations with English and Mandarin word tasks. The subject’s left hemisphere is on the right of each image. Thenumbers below the images are distances from the anterior commissural plane in the superior–inferior direction.

Fig. 4.

Correlation of the AI for English versus Mandarin in EB and LB subjects. AI = Sum (Voxels (L − R))/Sum (Voxels (L + R)).