Spatiotopic Coding of BOLD Signal in Human Visual Cortex Depends on Spatial Attention
Figure 1
MT and V1 BOLD response amplitude.
BOLD response amplitudes, averaged over subjects and hemispheres, as a function of the spatiotopic stimulus coordinates (0 is screen center), in MT (A & B) and parafoveal V1 (C & D), during passive fixation (A & C) and the foveal attentional task (B & D). The responses are color-coded by fixation (red −8°, black 0°, blue +8°: fixation indicated by the dotted colored lines). The mean responses were calculated by averaging the visual responses from homologous regions of the two hemispheres for mirror symmetric fixation directions and stimulus positions. Error bars show the between subject s.e.m., in many cases smaller than the symbol size. The responses of V1 are retinotopic, and became marginally more retinotopic in the attentional condition. In the passive viewing the responses of MT at all three fixations line up well, consistent with spatiotopic selectivity; with foveal attention they are clearly displaced in the direction of gaze, retinotopically tuned. Table S1 gives the values and significance of spatiotopic and retinotopic fits to the data.