Figure 2.

Retinotopic specificity of one of our unilateral stimuli in the contralateral (control) hemisphere. (A) Area boundaries based on the contralateral retinotopic map in one hemisphere (subject BK), produced by “thin” versions of bilateral, phase-encoded stimuli described earlier (24). (B) The effect of one of the present stimuli, avoiding the vertical meridian by 40°, in the same (contralateral) hemisphere of that subject, acquired during a different scan. As one would predict from the retinotopic map and from the present stimulus geometry (assuming stable fixation), the present stimulus produces robust activation within much of areas V1, V2, V3, VP, V3A, and V4v, including the representation of the contralateral horizontal meridian representations (solid lines). Activity also is concentrated toward the left border of the flattened map, which also coincides with a horizontal meridian representation in the midline of primary visual cortex. However, little or no activation was produced along the representation of the vertical meridia (dashed lines), nor along the foveal representation (∗). These features are consistent with the geometry of the contralateral stimulus, which also spared the vertical meridian and foveal representation, but included the horizontal meridian region. These results also confirmed the stability of fixation during the experiment. The other stimuli in this set, which encroached progressively closer to the vertical meridian, produced correspondingly more “filling in” of the vertical meridian representations; this finding is also consistent with the contralateral retinotopy (23–31). The pseudocolor activity representation is similar to that in Fig. 1. Increased MR signals in phase with grating presentation range from a display threshold of P > 0.01 (red) to a maximum of P > 10⁻¹¹ (white, surrounded by red). Regions of decreased MR signal level during grating presentation are rare in this hemisphere, but coded with a symmetrical color scale, from P > 0.01 (blue) to a minimum of P > 10⁻¹¹ (white, surrounded by blue). This data and data in subsequent figures are based on single scans (2,048 images), so maximal significance levels are correspondingly lower than those in Fig. 1. The location of sulci and gyri in the normal, folded cortical state are represented here in dark and light gray, respectively. The calibration bar represents 1 cm, without distortion correction; the distortion correction varies locally in the flattened maps but it typically averages +/− 15%.