A Hierarchical Axis of Object Processing Stages in the Human Visual Cortex

Abstract

How are objects represented in the human visual cortex? Two conflicting theories suggest either a holistic representation, in which objects are represented by a collection of object templates, or a part-based representation, in which objects are represented as collections of features or object parts. We studied this question using a gradual object-scrambling paradigm in which pictures of objects (faces and cars) were broken in a stepwise manner into an increasing number of blocks. Our results reveal a hierarchical axis oriented anterior--posteriorly in the organization of ventral object-areas. Along this axis, representations are arranged in bands of increasing sensitivity to image scrambling. The axis starts in early visual areas through retinotopic areas V4/V8 and continues into the lateral-occipital sulcus dorsally and the posterior fusiform girus ventrally, corresponding together to the previously described object-related lateral occipital complex (LOC). Regions showing the highest sensitivity to scrambling tended to be located at the most anterior-lateral regions of the complex. In these more anterior regions, breaking the images into 16 parts produced a significant reduction in activation. Interestingly, activation was not affected when images were cut in two halves, either horizontally or vertically. Car images generally produced a weaker activation compared to faces in the lateral occipital complex but showed the same tendency of increased scrambling sensitivity along the anterior--posterior axis. These results suggest the existence of a hierarchical axis along ventral occipito-temporal object-areas, in which the neuronal properties shift from sensitivity to local object features to a more global and holistic representation.

Global familiarity of visual stimuli affects repetition-related neural plasticity but not repetition priming

“…Interestingly, the presence of familiar object parts was sufficient to activate and then modulate these visual and semantic representations. Although it is also possible that the familiar parts of the U objects activated representations pertaining to whole objects in these regions, consistent with some prior findings (Lerner, Hendler, Ben-Bashat, Harel, & Malach, 2001), the slower rate of RS indicates that neural plasticity in these regions did depend on global perceptual and semantic stimulus properties.…”

“…Interestingly, the presence of familiar object parts was sufficient to activate and then modulate these visual and semantic representations. Although it is also possible that the familiar parts of the U objects activated representations pertaining to whole objects in these regions, consistent with some prior findings (Lerner, Hendler, Ben-Bashat, Harel, & Malach, 2001), the slower rate of RS indicates that neural plasticity in these regions did depend on global perceptual and semantic stimulus properties.The strong RS contribution to both F and U objects in the superior parietal lobule may signify a reduction in the amount of motor attention necessary to prepare the correct motor response for the repeated stimuli. Thus, superior parietal cortex has been shown to be involved in sensory-motor integration (Andersen, Snyder, Bradley, & Xing, 1997; Iacoboni, Woods, & Mazziotta, 1998;Tanabe, Kato, Miyauchi, Hayashi, & Yanagida, 2005) and motor attention (i.e., covert preparation of an upcoming movement, switching intended movements, hand-eye coordination) (Astafiev et al, 2003;Battaglia-Mayer & Caminiti, 2002;Rushworth, Johansen- Berg, Gobel, & Devlin, 2003).…”

Spatial attention facilitates selection of illusory objects: Evidence from event-related brain potentials

“…In the present experiment and in our previous study (Martinez et al, 2006), source analyses of the N1 associated with object-selective attention also indicated a principal neural generator in lateral occipital cortex (area LOC). Activation in this same LOC region has been observed in numerous object recognition studies using a variety of task stimuli, including objects defined by illusory contours (Mendola et al 1999;Murray et al 2004), partially occluded objects (Lerner et al 2001) and scrambled objects (Malach et al 1995). On the basis of these studies and others it has been suggested that the LOC region plays an important role in the encoding and recognition of objects.…”

Specialization within the ventral stream: the case for the visual word form area

“…The patch of cortex that responds to visual words is endowed with general functional properties. Those include its bias for foveal vs. peripheral images (Hasson et al, 2002), its location at an intermediate level of the hierarchy of visual areas (Grill-Spector et al, 1998) appropriate for object-level processing (Tarkiainen et al, 2002), and its sensitivity to local features vs. configural information (Gauthier et al, 2000;Lerner et al, 2001).…”