g., Simoncelli

and Olshausen, 2001), early processing stages along the visual hierarchy may extract these low-level feature covariances in orientation, curvature, and eccentricity (e.g., Carlson et al., 2011). Due to the large-scale organization of eccentricity in early visual cortex, this could give rise to pre-cursor object representations that are naturally arrayed along the cortical sheet by real-world size. Consequently an object’s real-world size would predict the location of its peak representation. A prominent alternative account for the large-scale spatial organization of object information is the connectivity-hypothesis proposed by Mahon and Caramazza, which argues that object representation is driven by long-range network connectivity (Mahon and Caramazza, BI 6727 nmr 2011 and Mahon et al., 2007). On this account, manipulable objects like tools require different “downstream” action requirements

than animate objects like buy Torin 1 animals, and this determines the organization of ventral stream representations. Interestingly, the real-world size of objects naturally constrains the kinds of actions and effectors that will be used when an observer interacts with an object (e.g., with the fingers, hands, arms, or full body). By incorporating the notion of real-world size into action requirements, it may be possible to extend their proposal beyond animals and tools to the large range of other biological and manmade artifacts. Thus, real-world object size may not only be related to the eccentricity and shape features of objects, but may also be a natural proxy for different classes of action

and interaction types, as reflected in ventral-dorsal connectivity. While the eccentricity-bias and connectivity-driven hypothesis have often been discussed as competing alternatives, our real-world size account may unify these proposals, as here we propose both bottom-up experience-driven learning and top-down requirements for action provide convergent pressures for object knowledge to be topographically organized by real-world size. Twenty-two healthy observers with normal or corrected-to-normal vision participated in one or more of the experiments in a 2 hr fMRI session (age 19–36, 13 female, 21 right-handed). Informed consent was obtained according to procedures approved by the MIT Internal Review Board. Imaging data were collected on a unless 3T Siemens fMRI Scanner at the Martinos Center at the McGovern Institute for Brain Research at MIT. Experiments 1 and 2 used a 12-channel phased-array head coil and Experiment 3 used a 32-channel phased-array head coil. Blood oxygenation level-dependent (BOLD) contrast was obtained with a gradient echo-planar T2∗ sequence (33 oblique axial slices acquired parallel to the anterior commissure-posterior commissure line; 64 × 64 matrix; FoV = 256 × 256 mm; 3.1 × 3.1 × 3.1 mm voxel resolution; Gap thickness = 0.62 mm; TR = 2000 ms; TE = 30 ms; flip angle = 90 degrees).