The neural development and organization of letter recognition: Evidence from functional neuroimaging, computational modeling, and behavioral studies

The neural development and organization of letter recognition: Evidence from functional neuroimaging, computational modeling, and behavioral studies

Thad A. Polk*,† and
Martha J. Farah‡

^*Department of Psychology, University of Michigan, 525 E. University, Ann Arbor, MI 48109-1109; and ^‡Department of Psychology, University of Pennsylvania, 3815 Walnut Street, Philadelphia, PA 19104-6196

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Figure 1
Significant differences in the blood-oxygenation level-dependent (BOLD) MRI signal during passive viewing of letters vs. digits (L-D), digits vs. letters (D-L), and shapes vs. letters and digits (S-LD) (T.A.P., M. Stallcup, G. K. Aguirre, D. Alsop, M. D’Esposito, J. Detre & M.A.F., unpublished work). For each of the three comparisons in each of the six sessions, the single horizontal brain slice that showed the most significantly activated voxels for that comparison is shown. Voxels in yellow were significant at the P < 0.05 level after correcting for all the voxels as well as for the three planned comparisons. Voxels in red were significant at the P < 0.1 level, corrected. The left hemisphere appears on the left and the right hemispheres on the right.
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Figure 2
The state of the network after 1, 3, and 5 processing cycles when a pair of letters is presented (top row) and when a pair of digits is presented (bottom row) (7). The input layer is on the left, and state of the output layer after 1, 3, and 5 processing cycles is on the right. [Reproduced with permission from ref. 7 (Copyright 1995, Proceedings of the National Academy of Sciences)].
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Figure 3
The state of the neural network after five epochs of training under varying initial conditions (7). The left of each pair shows the activation when all eight letters are present, and the right shows the activation when all eight digits are present. [Reproduced with permission from ref. 7 (Copyright 1995, Proceedings of the National Academy of Sciences)].
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Figure 4
Mean reaction time (with SE bars) for correct responses on target-present trials for 16 postal worker controls, the 13 fastest postal worker controls, 8 college graduates, and 10 foreign mail sorters.