Independent representation of parts and the relations between them: Evidence from integrative agnosia.

Abstract

Whether objects are represented as a collection of parts whose relations are coded independently remains a topic of ongoing discussion among theorists in the domain of shape perception. S.M., an individual with integrative agnosia, and neurologically intact ("normal") individuals learned initially to identify 4 target objects constructed of 2 simple volumetric parts. At test, the targets were mixed with distractors, some of which could be discriminated from the targets on the basis of a mismatching part, whereas the rest could be discriminated only on the basis of the altered spatial arrangements of parts. S.M. learned to identify the target objects, although at a rate slower than that of the normal participants. At test, he correctly rejected distractors on the basis of mismatching parts but was profoundly impaired at rejecting distractors made of the same local components but with mismatching spatial arrangements. These results suggest that encoding the spatial arrangements of parts of an object requires a mechanism that is different from that required for encoding the shape of individual parts, with the former selectively compromised in integrative agnosia.

Greater sensitivity to nonaccidental than metric changes in the relations between simple shapes in the lateral occipital cortex

“…The lack of differential activities in earlier ventral pathway stages was, perhaps, to be expected given the equivalence in the pixel energy and Gabor-jet scaling of the NAP and MP differences. The finding of greater BOLD responses in LO to the NAP over the MP condition is consistent with recent findings that LO is a critical region for the coding of the relative positions of objects (Hayworth et al, 2011; and within parts of an object (Behrmann et al, 2006;Lescroart and Biederman, 2012).…”

Size Precedes View: Developmental Emergence of Invariant Object Representations in Lateral Occipital Complex

“…Left ventral lesions do not typically give rise to profound agnosia, and instead, tend to result in deficits in visual word recognition (Behrmann et al, 1998;McKeeff and Behrmann, 2004). This asymmetry is supported in our patient sample, with the right ventral patients more profoundly impaired in object recognition than the left ventral patients (Behrmann et al, 2006). Since visual motion usually occurs when an object with a particular form is moving, we speculate that motion processing is tightly linked to form processing (Kourtzi et al, 2008) even for non-form motion, and therefore, the right ventral visual dominance for form perception might serve as the basis of the motion perception laterality effect we have observed in this study.…”

Visual complexity exerts opposing effects on object categorization and identification

“…On its own this does not explain why shape configuration (the binding of visual elements) is necessary in the first place. Recurrent processing could occur without involving shape configuration, but evidence suggests that this is not sufficient to support identification when perceptual differentiation becomes hard and many features must be considered simultaneously (Behrmann, Moscovitch, Peterson, & Suzuki, 2006;Behrmann & Williams, 2007) as is the case in difficult object decision (Gerlach et al, 2005). It is also worth noting that even though an extended verification/checking process can explain the overall longer RTs during object decision compared with categorization-and this is regardless of whether the verification/checking process continues after the shape has been resolved-it would not explain why RTs depend on visual complexity.…”