Background: The recent advent of non-invasive functional magnetic resonance image (fMRI) has helped us understand how visual information is processed in the visual system, and the functional organising principles of high-order visual areas beyond striate cortex. In particular, evidence has been reported for a constellation of high-order visual areas that are highly specialised for the visual processing of different object domains such as faces, bodies, and tools. A number of accounts of the underlying principle of functional specialisation in high-order visual cortex propose that visual properties and object domain drive the category selectivity of these areas. However, recent evidence has challenged such accounts, showing that non-visual object properties and connectivity constraints between specialised brain networks can, in part, account for the visual system’s functional organisation. Methodology: Here I will use fMRI to examine how areas along the visual ventral stream and dorsal action stream process visually presented hands and tools. These categories are visually dissimilar but share similar functions. By using different statistical analyses, such as univariate group and single-subject region of interest (ROI) analyses, multivariate multivoxel pattern analyses, and functional connectivity analyses, I will investigate the topics of category-selectivity and the principles underlying the organisation of high-order visual areas in left occipitotemporal and left parietal cortex. Principle Findings: In the first part of this thesis I report novel evidence that, similar to socially relevant faces and bodies, the human high-order visual areas in left occipitotemporal and left parietal cortex houses areas that are selective for the visual processing of human hands. In the second part of this thesis, I show that the visual representation of hands and tools in these areas show large anatomical overlap and high similarity in the response patterns to these categories. As hands and tools differ in visual appearance and object domain yet share action-related properties, the results demonstrate that these category-selective responses in the visual system reflect responses to non-visual action-related object properties common to hands and tools rather than to purely visual properties or object domain. This proposition is further supported by evidence of selective functional connectivity patterns between hand/tool occipitotemporal and parietal areas. Conclusions/Significance: Overall these results indicate that high-order visual cortex is functionally organised to process both visual properties and non-visual object dimensions (e.g., action-related properties). I propose that this correspondence between hand and tool representations in ventral ‘visual’ and parietal ‘action’ areas is constrained by the necessity to connect visual object information to functionally-specific downstream networks (e.g., frontoparietal action network) to facilitate hand-tool action-related processing.
|Publication status||Accepted/In press - 8 Aug 2011|