To define brain regions involved in feature extraction
or elementary form perception, regional cerebral blood
flow (rCBF) was measured using positron emission tomography
(PET) in subjects viewing two classes of achromatic textures.
Textures composed of local features (e.g. extended contours
and rectangular blocks) produced activation or increased
rCBF along the occipitotemporal pathway relative to textures
with the same mean luminance, contrast, and spatial-frequency
content but lacking organized form elements or local features.
Significant activation was observed in striate, extrastriate,
lingual, and fusiform cortices as well as the hippocampus
and brain stem. On a scan-by-scan basis, increases in rCBF
shifted from the occipitotemporal visual cortices to medial
temporal (hippocampus) and frontal lobes with increased
exposure to only those textures containing local features.
These results suggest that local feature extraction occurs
throughout the occipitotemporal (ventral) pathway during
extended exposure to visually salient stimuli, and may
indicate the presence of similar receptive-field mechanisms
in both occipital and temporal visual areas of the human