Orthographic transparency modulates the functional asymmetry in the fusiform cortex: an artificial language training study

Abstract

The laterality difference in the occipitotemporal region between Chinese (bilaterality) and alphabetic languages (left laterality) has been attributed to their difference in visual appearance. However, these languages also differ in orthographic transparency. To disentangle the effect of orthographic transparency from visual appearance, we trained subjects to read the same artificial script either as an alphabetic (i.e., transparent orthography) or a logographic (i.e., nontransparent orthography) language. Consistent with our previous results, both types of phonological training enhanced activations in the left fusiform gyrus. More interestingly, the laterality in the fusiform gyrus (especially the posterior region) was modulated by the orthographic transparency of the artificial script (more left-lateralized activation after alphabetic training than after logographic training). These results provide an alternative account (i.e., orthographic transparency) for the laterality difference between Chinese and alphabetic languages, and may have important implications for the role of the fusiform in reading.

Fig. 1

Experiment design and examples of the stimuli. The artificial language was created by adopting the visual forms and sounds of 60 Korean Hangul characters. Two matched groups of subjects received alphabetic and logographic training (A) for eight days (one hour per day). Before and after training, subjects were scanned when performing a perceptual task (B), in which subjects were asked to respond to the underlined words.

Fig. 2

Accuracies (A) and reaction times (B) of trained and untrained artificial words for the alphabetic and logographic groups. Error bars represent the standard error of the mean.

Fig. 3

Training-related changes in activations for the artificial words in the alphabetic and logographic groups. All activations were thresholded at z > 2.3 (whole-brain corrected), and and rendered onto PALS-B12 atlas (Van Essen, 2002, 2005) via average fiducial mapping using caret software (Van Essen et al., 2001).. R = Right; FG = fusiform gyrus.

Fig. 4

The between-group (alphabetic and logographic) differences in fusiform laterality for the artificial words. Percent signal changes were extracted from the left and right anterior, middle, and posterior fusiform regions at pre- and post-training stages. The laterality index (vertical coordinate) was calculated by comparing the percent signal change in the left and right regions. Error bars represent the standard error of the mean.