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FIG. 1. Topography of primary visual cortex and surrounding areas. (A and B) Field sign analysis (12, 13) of retinotopic cortical visual areas from right and left hemispheres (respectively) in a single subject. Both hemispheres are views of the medial bank, in its normal, folded configuration. Thus in A, anterior is to the left, and posterior to the right. In B, this is reversed. The field sign maps are based on two scans measuring polar angle (rotating thin ray stimulus), and two scans measuring eccentricity (expanding thin ring stimulus), acquired from echo-planar images in a 3-T scanner (General Electric/ANMR), using a bilateral, send/receive quadrature coil. Both stimuli extended 18–25° in eccentricity (36–50° extent). (C and D) Same data, in a cortically “inflated” format, now viewed from a more posterior-inferior vantage point. Again the left panel shows the right hemisphere, and the right panel shows the left hemisphere from the same subject. Human retinotopic areas revealed by the field sign analysis have been labeled (V1, V2, V3, VP, V3A, V4v). Cortical areas with a visual field sign (polarity) similar to that in the actual visual field are coded blue, and those areas showing a mirror-reversed field polarity are coded yellow. Also labeled is the foveal representation in V1 (black asterisks). Gyri and sulci in the folded state (e.g., A and B) are coded in lighter and darker shades of gray (respectively) in the inflated format (C and D). In this subject, area V1 is somewhat larger than normal, extending well past the lips of the calcarine fissure. However, as in most subjects, the V1 representation of the extrafoveal horizontal meridian lies near the fundus of the calcarine fissure.

viewed from a posterior inferior viewpoint. In this subject, V1 extends further beyond the lips of the calcarine fissure, and onto the lateral surface, compared with most subjects.

In a previous study using the deoxyglucose labeling technique, the internal retinotopy of macaque V1 was revealed by stimulating with stationary, flickering, retinotopically specific check stimuli based on polar geometry (rays and rings) (34, 35). To judge more accurately the degree of similarity between humans and macaques, here we did an analogous experiment in human V1, using fMRI.

The present experiment was redesigned slightly to match two differences of the fMRI technique: (i) poorer spatial resolution, but (ii) an unlimited number of activity maps, from each fMRI subject. Here we stimulated with spatially alternating flickering check stimuli grouped into one of the following: (i) isopolar angle “wedges”, (ii) isoeccentricity “rings”, or (iii) circles of equal polar-angle diameter.

These stimuli, and the results of this stimulation, are shown in Fig. 2. Data from three scans are shown. For each scan the stimuli are shown in S1–2, S3–4, and S5–6, and the corresponding activity is shown in A plus B, C plus D, and E plus F, respectively. The activities produced by the first and second retinotopic stimuli (in each scan) are shown in red and green (respectively) in the activity maps. The activity maps are illustrated from the same hemispheres shown in Fig. 1. but now are rendered on fully flattened portions of the cortical surface.

As one might expect from a roughly polar retinotopy in macaque V1: (i) the isopolar-angle wedges produce roughly equal width, roughly parallel stripes in cortex; (ii) the isoeccentric rings of radially varying width produce stripes of roughly equal width, oriented approximately orthogonal to those in i; and finally (iii) the circles of radially varying stimulus diameter produced circular activity patches, of roughly equal cortical width. The retinotopic patterns do not extend far into



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