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D. Merika W. Sanders, Rosemary A. Cowell; Localizing feature- and conjunction-coding in the ventral visual pathway for objects and scenes. Journal of Vision 2020;20(11):1453. doi: https://doi.org/10.1167/jov.20.11.1453.
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The hierarchical organization of stimulus representations in the ventral visual stream is well documented by findings from electrophysiology in animals and neuroimaging in humans. We have long known that feature-coding (representing low-level image properties) is dominant early in the ventral visual stream, whereas conjunction-coding (representing object-parts and objects) is dominant in later ventral visual stream areas. A recent study confirmed and localized the existence of a transition from feature- to conjunction-coding (i.e., the point at which neural representations become less informative about individual features and more informative about the conjunction of those features) for simple object stimuli. Here, we extend these findings to more complex stimulus sets, testing two central assumptions of the representational-hierarchical account of cognition: (1) that the transition from feature-coding to conjunction-coding extends into anterior ventral visual stream and medial temporal lobe, and (2) that the location of the transition depends on the complexity of the stimuli. Participants in the scanner performed 1-back repetition-detection while viewing two stimulus sets with different levels of complexity: fribbles (novel 3D objects) and scenes (novel, computer-generated rooms). Each unique stimulus was composed of three simple, binary features; by using all possible combinations of the three features we created a “family” of stimuli in which items shared many features but were each defined by a unique conjunction. A multivariate analysis of functional imaging data designed to reveal dominance of feature-coding vs. conjunction-coding for these stimuli revealed that the transition from feature- to conjunction coding was located further posterior in the ventral visual stream for objects than for scenes. This confirms the existence of a continuum of representations for complex stimuli, and suggests that the location of “conjunction” representations in the brain depends on the complexity of the conjunction.
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