Fig. 1 .  Schematic representations of visual sequence. (A) Schematic representation of a trial in the visual modality. Each trial started with a fixation point that lasted for 500 ms, followed by the stimuli (a sequence of 30 visual or auditory events), that lasted for about 6.5 s, and ended with a question mark, after which subjects could give their answer, within 1.5 s, via key pressing. (B) One exemplar sequence of stimuli in the visual modality (30 stimuli grouped in 7 clusters).

Fig. 2 .  Cortical regions of increased activation common to visual and auditory modality for estimation and counting. Group results (n = 10, P < 0.05 corrected at the cluster level) are visualized on a three-dimensional rendering showing the left, right, and top views of the hemispheres. Plots show the activation of the (1) right middle frontal gyrus, (2 and 5), right and left precentral gyrus, (3 and 6) right and left anterior intraparietal cortex, (4) medial precentral gyrus peaks of the random effect analysis as a function of the 6 different experimental conditions (visual (V) and auditory (A) estimation (E), counting (C), and matching (M) tasks). Error bars represent standard errors of the mean (SEM). See Table 1  and Table 2  for the co-ordinates of the clusters.

Fig. 3 .  Cortical regions of increased activation common to visual and auditory modality for counting with respect to estimation. Group results (n = 10, P < 0.05 corrected at the cluster level) are visualized on a three-dimensional rendering showing the left, right, and top views of the hemispheres. Plots show activation of the (7) medial precentral gyrus and (8 and 9) left and right precentral gyrus as a function of the 6 different experimental conditions (visual (V) and auditory (A) estimation (E), counting (C), and matching (M) tasks). Error bars represent SEM. See Table 3 for the co-ordinates of the clusters.

Fig. 4 .  Plots of the task-related hemispheric dissociation. Top left is the mean activation level across subjects for the peak of the random effect analysis of the anterior intraparietal cortex as a function of the task and the hemisphere. Top right is the mean activation for each of the ten participants. Bottom is the mean activation across subjects for the precentral cortex peak. Error bars represent SEM. Numbers next to the x-axes indicates the regions labeled in Fig. 2 (co-ordinates in Table 1  and Table 2 ).

Fig. 5 .  Schematic representation of the temporal structure of the experiment.

 Estimation > matching

 Counting > matching

 Counting > estimation