CORTICAL REGIONS INVOLVED IN VISUAL TEXTURE-PERCEPTION - A FMRI STUDY

To determine visual areas of the human brain involved in elementary fo rm processing, functional magnetic resonance imaging (fMRI) was used t o measure regional responses to two types of achromatic textures. Heal thy young adults were presented with 'random' textures which lacked sp atial organization of the black and white pixels that make up the imag e, and 'correlated' textures in which the pixels were ordered to produ ce extended contours and rectangular blocks at multiple spatial scales . Relative to a fixation condition, random texture stimulation resulte d in increased signal intensity primarily in the striate cortex, with slight involvement of the cuneus and middle occipital, lingual and fus iform gyri. Correlated texture stimulation also resulted in activation of these areas, yet the regional extent of this activation was signif icantly greater than that produced by random textures. Unlike random s timulation, correlated stimulation additionally resulted in middle tem poral activation. Direct comparison of the two stimulation conditions revealed significant differences most consistently in the anterior fus iform gyrus, but also in striate, middle occipital, lingual and poster ior temporal regions in subjects with robust activation patterns. Whil e both random and correlated stimulation produced activation in simila r areas of the occipital lobe, the increase in regional activation dur ing the correlated condition suggests increased recruitment of neurona l populations occurs in response to textures containing visually salie nt features. This increased recruitment occurs within striate, extrast riate and temporal regions of the brain, also suggesting the presence of receptive field mechanisms in the ventral visual pathway that are s ensitive to features produced by higher-order spatial correlations. (C ) 1998 Elsevier Science B.V. All rights reserved.