The “Parahippocampal Place Area” Responds Preferentially to High Spatial Frequencies in Humans and Monkeys
Figure 1
The higher-order cortical area PPA responds differentially to cubes versus spheres.
(A) Sphere and cube stimuli and their FFTs. The top row shows sample images of the “smooth” sphere and the “smooth” cube. The bottom row shows the averaged 2-D FFT of the four sphere (left) and the four cube (right) images. The four images were distinguished only by changes in the location of the illuminant (see Materials and Methods). The red/blue color map represents the FFT magnitude (magnitude = red > yellow > cyan > blue) in Fourier space; the center of this space indicates the DC component of the FFT. The spectral distribution included a complex pattern of high SF components in the cube, but not in the sphere. Here and in the other FFT maps, the SF units are in cycles per pixel. (B) As a control, we produced an fMRI map based on a conventional, blocked-design comparison of naturalistic face versus place images, in five human subjects (using independent localizer scans). The group-averaged activity map is displayed on a ventral view of the averaged inflated cortical surface; the left hemisphere is shown on the right, with anterior towards the top. Faces and places produced relatively higher activity in FFA and PPA, respectively. (C) Relative activation to the cube versus the sphere is based on the averaged data, from the same five subjects shown in (B). The cube activated PPA robustly and selectively, with a topography similar to that produced by place-based activation. The color scale bars in the cortical maps here and in the other figures indicate the p-values, in a logarithmic format (i.e., −log10[p]).