Location of VWFA in relation to the visual field maps in a typical subject. (Upper Left) fMRI retinotopic mapping was performed to define visual field map boundaries (blue) for V1, V2, V3, hV4, VO-1, VO-2, LO-1, LO-2, TO-1, and TO-2. (Lower Left) Separate runs of the VWFA localizer were performed, and voxels were chosen on the basis of the contrast words > phase-scrambled words at a threshold of P < 0.001 (uncorrected, orange overlay). VWFA voxels were restricted to be outside of known retinotopic areas and anterior to hV4 in ventral occipito-temporal cortex. (Right) The cortical surface of the posterior left hemisphere is rendered as a mesh and computationally inflated to visualize the sulci (dark gray). The majority of VWFA voxels (red) are located lateral or anterior to VO-1/VO-2 in all subjects. The TO-1/TO-2 maps overlap with the human motion complex (hMT+). Fus, fusiform gyrus; OTS, lateral occipitotemporal sulcus. (Scale bar: 10 mm.) Subject is S1.

Classification of visual field position using VWFA responses. The classifier was trained using data from several regions of interest (ROI): V1/V2, VWFA, rVWFA, and Broca’s area. The “combined” region of interest is the union of voxels from VWFA and rVWFA. Classification accuracy was measured in individual subjects. When tested on data from untrained trials, the classifier performance is above chance for left vs. right (Upper) and upper vs. lower (Lower) visual field (VF) classification in all regions except Broca’s area. The short horizontal lines indicate the mean classifier performance within an ROI and across subjects. The dashed line indicates chance performance (50%), and the line with light shading indicates the significance level (P < 0.05) derived by a bootstrap procedure. In some sessions, because of the MR slice prescription, a Broca’s area ROI was not measured.

Retinotopic organization of classifier weight maps in single subjects. Voxels are colored according to the weight assigned by the classifier. Positive weights (corresponding to voxels that identify upper VF stimuli) are red, and negative weights (corresponding to voxels that identify lower VF stimuli) are blue. Brightness represents the weight (see color bar). Values are normalized within each region of interest and thresholded at 10% of the maximum value. The columns show the classifier weight maps for words at 1°, 3°, and 6° above or below fixation separately. (Top) Stimulus eccentricity. (Middle) Maps from V1/V2. (Scale bar, 10 mm.) (Bottom) Maps from VWFA. (Scale bar, 4 mm.) The classifier weight map for differentiating all upper from all lower VF stimuli is shown in the rightmost column. (Middle row, subject S2; Bottom row, subject S3)

Confusion matrices support a retinotopic map in VWFA. The rows represent the true stimulus position; the columns represent the classified position. The color indicates the probability of measuring a stimulus-classification pair across all trials of that stimulus position. Correct classifications are on the diagonal and misclassifications are off the diagonal. The confusion matrices shown are the average of the individual subject confusion matrices (n = 6). (Left) V1/V2 classifier performance is very high. (Right) VWFA classification performance is lower, but misclassifications are largely confined to neighboring stimulus positions. U, upper VF; L, lower VF. One degree, 3°, and 6° refer to distances from the center of fixation. The color bar at the right represents the classification probabilities, and the black line indicates the chance level (16.7%).

VWFA and rVWFA time course amplitudes are larger for contralateral than for ipsilateral word stimuli. (Left and Right) fMRI time courses from the VWFA and the rVWFA, respectively. (Upper) Responses to words in the left (blue) and right (red) VF. (Lower) Responses to words in the upper (red) and lower (blue) VF. Both the VWFA and the rVWFA respond preferentially to contralateral stimuli. The laterality index (main text) is shown in the Inset at the Right. There is no significant response difference between words in the upper and lower VF. Error bars are ±1 SEM, computed across subjects.

Electrocorticographic VWFA responses to ipsilateral stimuli are delayed compared to responses to contralateral stimuli. (A) A 3D reconstruction showing the VWFA and electrode positions. The patient’s left hemisphere is shown from a ventral view. Blue disks indicate estimated electrode positions. The red disk is the electrode overlying the VWFA. The dashed line is a coronal plane, shown below. Functional MRI data contrasting words > phase-scrambled words (threshold P < 0.001, uncorrected; orange-yellow) reveal the VWFA location in this subject. The third image (Bottom) is a magnified view showing the electrode of interest (red), two neighboring electrodes (blue), and the VWFA. See also Fig. S4B. (B) Median VWFA response times to letter strings in different visual field locations. The graph shows the median response onset latency of the high-gamma signal (±1 SEM) across trials (n = 180 for green foveal condition; n = 40 for all other conditions). Colored outlines indicate the stimulus position relative to fixation, shown at the Right. Conditions included words, pseudowords, or consonant strings. (C) Cumulative distribution of single trial responses. The cumulative fraction of trials (y axis) is shown as a function of response onset latency (x axis). The curve for ipsilateral stimuli (red) is substantially to the right (delayed) compared with all other conditions. Stimulus conditions: green, foveal, four-letter, six-letter, and eight-letter; red, ipsilateral, four-letter; blue, contralateral, four-letter; light gray, ipsilateral with foveal component, eight-letter; dark gray, contralateral with foveal component, eight-letter.

A new circuit diagram for visual word form processing. (A) Parafoveal stimuli produce distinct clusters of activity in visual cortex that can be measured in individual subjects. A contrast map between words in the right and left visual field (3° eccentricity, right > left) is shown on an inflated ventral posterior left hemisphere of one subject (P < 0.001, uncorrected; orange-yellow). The visual field map and VWFA positions, derived in separate experiments, are also shown. The red square on the ventral view of the left hemisphere (Inset Upper Left) indicates the magnified region. (B) In the new circuit diagram multiple visual field maps perform a feature-tolerant and position-sensitive transformation, which yields an abstract shape representation in the VWFA (). The position-sensitive VWFA and the rVWFA responses may interact and communicate word form information to the language system. Black lines indicate possible processing pathways. LH, left hemisphere; RH, right hemisphere. Subject is S2.

(A) In some experimental blocks, words were shown to subjects in either the upper visual field (red) or the lower visual field (blue). The red circle outlined in black corresponds to the center of the subjects’ gaze. Whether words during a particular trial were in the upper or the lower visual field can be decoded on the basis of the fMRI responses from both early visual cortex (Upper) and the VWFA (Lower). The area within each region that best predicts whether the word was in the upper or the lower visual field is colored in red or blue, respectively. The regions corresponding to the upper and lower visual fields separate well in space within both regions. (B) In other experimental blocks, words were shown to subjects in the left visual field (red) or the right visual field (blue). Again, the location of the word can be decoded from the response in the VWFA or in the right-hemisphere VWFA (rVWFA). In this case, the response is approximately twice as strong for words in the opposite visual field as for words in the visual field on the same side, so the location of the word can be predicted simply on the basis of response strength.