Properties of Object Processing in Lateral Occipital Cortex

Christopher W. Tyler, Lora T Likova and Alex R. Wade

Studies of the cortical activation by images of objects relative to scrambled versions of the same stimuli typically find that object-specific activity measured by functional Magnetic Resonance Imaging (fMRI)is centered on a swath of regions of lateral occipital cortex, extending through the lateral occipital cortex (LO), from the intraparietal sulcus dorsally to the fusiform gyrus ventrally. By selective stimulus comparisons, we partitioned the properties of object responses into the components of: contour continuity, depth, symmetry, familiarity, and a joint factor of objectness in general.  The fMRI responses were recorded in a block design on a 3T GE Signa scanner in 23 slices spanning the occipital lobes in six observers.  The primary retinotopic areas responded more strongly to scrambled than intact objects (despite the presence of equated local contours) implying that the fMRI shows a stronger retinotopic response for the local components alone than for the same components in the presence of elongated contours.  This response pattern implies that long-range structure suppresses the responses of local receptive fields.

In LO as a whole, the comparisons revealed a patchwork of differential response to the component properties.  Object depth generated specific responses in dorsomedial LO, an area corresponding to the kinetic occipital area for motion-defined shapes (KO), and in another area in the occipital IPS.  Object symmetry activated regions in medial and ventral LO near motion area V5.  Object familiarity activated distinct regions, ventrally near area V4 and dorsally near area V3A.  Such feature-specific response segregation reveals that the object-responsive network is composed of identifiable components with topographic specialization for different aspects of object identity.

Supported by EY 13025.