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Ori Amir, Kenneth Hayworth, Irving Biederman, Mark Lescroart, Xiaokun Xu, Jiye Kim; At what stage in the human ventral pathway is the greater sensitivity to nonaccidental over metric properties first manifested?. Journal of Vision 2009;9(8):810. doi: https://doi.org/10.1167/9.8.810.
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Non-accidental shape properties (NAPs) are those that are invariant under rotation in depth, such as whether a contour is straight or curved. Metric properties (MPs), such as the degree of curvature of a contour, can vary continuously with depth rotation. NAPs allow facile recognition when an object is viewed at an orientation not previously experienced. At what stage in the ventral pathway is the greater sensitivity to NAPs over MPs first manifested? In a single block, subjects viewed five brief animations of single geons that either cycled (through 8 frames/animation) between a NAP or an MP change or a Rotation in depth (around both the X and Y axis). For example, a NAP animation could be a cylinder with an axis cycling between being slightly curved to straight. The MP animation could be the slightly curved axis cycling with a more curved axis. Pixel energy changes were equated for the three kinds of animations. Subjects were to detect, by key press, whether there was a repeat of an animation within a block. BOLD signals were consistently and reliably greater for NAP than MP differences in LOC (both in LO and pFs) with Rotation magnitudes falling, on average, in between those of the NAP and MP conditions (in pFs). These effects were not apparent in earlier cortical stages, e.g., V1. Insofar as macaque IT cells show a greater modulation of NAP over MP differences, these results support the interpretation that human LOC is a functional homologue to macaque IT.
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