r Seghier et al. r corrected-to-normal vision, and had no history of neuro- logical or psychiatric disorders. Their handedness was assessed with the Edinburgh questionnaire [Oldﬁeld, 1971]: 44 were right-handed and 38 were either left- handed or ambidextrous. Their age ranged from 13 to 71 years: 21 subjects under 20 years old, 43 subjects between 20 years and 40 years old, and the remaining 18 subjects were more than 60 years old (mean ¼ 30.3 15 years). The study was approved by the National Hospital for Neurology and Institute of Neurology Joint Ethic’s Committee Task and Experimental Design Our semantic word matching task involved categoriza- tion of three visually presented words, each with one tar- get above and two choices below. The subject is required to indicate which of the two choices below is most seman- tically related to the target above. The baseline task involved the same spatial display of three items but words were replaced with strings of unfamiliar greek letters and participants were instructed to indicate which of the two choices looked identical to the target above. For both tasks, the participants indicated their response on a key pad with either the index and middle ﬁnger on their right hand indicating the lower left or lower right stimulus respectively (50 subjects) or the middle and index ﬁnger on their left hand indicating the lower left or lower right stimulus respectively (32 subjects). Comparison of the semantic to the perceptual decisions reliably identiﬁes semantic activations and their laterality (e.g., [Josse et al., 2008; Vandenberghe et al., 1996]). In addition to the semantic decisions on words and per- ceptual decisions on greek letters, the experiment also included semantic matching on photographs of familiar objects and perceptual matching on photographs of unfa- miliar nonobjects. All stimuli during the two semantic matching conditions were derived from a set of 192 objects with three to six letter familiar names (e.g., cat, bus, hat, ship, bell, frog, hand, teeth, camel, snake, spider, dagger, and button) that were ﬁrst divided into two different sets of 96 items. Half of subjects were presented with the ﬁrst set of 96 items as written words and the second set of 96 items as pictures, and the other half of subjects were pre- sented with the reverse order of sets. Post hoc checks ensured that inter-subject variability in lateralization could not be explained by the stimulus set. Conditions and sets were fully counterbalanced within and across subjects. The two additional conditions of pic- tures of familiar and unfamiliar objects are not the focus of the current paper but they were used in post hoc tests to examine functional specialization in regions within the semantic word matching network. The four conditions were counterbalanced within each of two experimental runs/sessions. Across sessions, there were 32 stimuli pre- senting triads of written words, 32 stimuli presenting tri- ads of pictures of objects, 16 stimuli presenting triads of greek letters and 16 stimuli presenting triads of unfamiliar nonobjects. Each stimulus (trial) stayed on the screen for 4.32 s followed by 180 ms ﬁxation before the next stimu- lus. To maximize efﬁciency, four stimuli of the same type were presented successfully (i.e., blocks of 18 s). In addi- tion, we included 12 blocks of ﬁxation, each lasting 14.4 s, every two stimulus blocks. To facilitate task switching, each block was preceded by a written instruction for 3.6 s (e.g., ‘‘match words’’). Stimulus presentation was via a video projector, a front- projection screen and a system of mirrors fastened to a head coil. To ensure that the task was understood cor- rectly, all subjects were provided with detailed instruc- tions and underwent a short training session before entering the scanner with a different set of stimuli. Addi- tional details about the paradigm and stimuli can be found in our previous work (c.f., [Josse et al., 2008]). MRI Acquisition Experiments were performed on a 1.5T Siemens system (Siemens Medical Systems, Erlangen, Germany). Func- tional imaging consisted of an EPI GRE sequence (repeti- tion time/echo time/ﬂip angle ¼ 3,600 ms/50 ms/90 , ﬁeld of view ¼ 192 mm, matrix ¼ 64 64, 40 axial slices, 2 mm thick with 1 mm gap). Functional scanning was always preceded by 14.4 s of dummy scans to insure tis- sue steady-state magnetization. Anatomical T1-weighted images were acquired using a three-dimensional modiﬁed driven equilibrium Fourier transform sequence (repetition time/echo time/inversion time ¼ 12.24 ms/3.56 ms/530 ms, matrix ¼ 256 224, 176 sagittal slices with a ﬁnal re- solution of 1 mm3). fMRI Data Preprocessing Data processing and statistical analyses were performed with the Statistical Parametric Mapping SPM5 software package (Wellcome Trust Centre for Neuroimaging, Lon- don UK, http://www.ﬁl.ion.ucl.ac.uk/spm/). All func- tional volumes were spatially realigned, unwarped, and normalized to the MNI space using the uniﬁed normaliza- tion-segmentation procedure [Ashburner and Friston, 2005] with resulting voxels size of 2 2 2 mm3. Symmetrical Images The priors used during the normalization-segmentation step were a symmetrical version of the default priors implemented in SPM5. These symmetrical priors were cre- ated by simply copying, ﬂipping along the x-axis, and averaging the original and the mirror (ﬂipped) versions of the priors [Salmond et al., 2000]. The resulting normaliza- tion-segmentation parameters were then applied to the subject’s functional images thereby rendering them r 1604 r