Helen E. Feibes¹, Spencer R. Loggia^1,2, Karthik Kasi¹, Bevil R. Conway¹; ¹Laboratory of Sensorimotor Research, National Eye Institute, National Institutes of Health, ²Department of Neuroscience, Brown University

Object concepts defined by color-plus-shape are important tools of cognition. For example, they enable inferences about missing or mismatching perceptual data, providing a mental picture that guides visual search. The brain regions and associated processes responsible for storing object concepts remain poorly understood. One hurdle has been that concepts and patterns of brain activity vary among individuals; moreover, the subjective value associated with different concepts varies. Here we overcome these challenges by training two macaque monkeys to learn about 12 objects, each defined by a unique color and shape. After four years of experience with these objects, we pairwise swapped their colors, generating 12 ‘incongruent’ objects. We then took fMRI scans while the monkeys viewed blocks of congruent objects (the learned color-shape pairs) and incongruent objects. All colors and shapes were the same between incongruent and congruent objects, as was the reward associated with them. This enabled us to isolate brain regions that are sensitive to the specific conjunctions, providing a way of determining where in the brain color-shape knowledge is stored. Prior work has generated two main hypotheses: that knowledge is stored in sensory processing regions, or it represented abstractly elsewhere. Incongruent objects preferentially activated large parts of V2, V3, V4, and posterior-central IT (average selectivity .046; 95% CI (.036, .056)), and trended upwards along the posterior-to-anterior axis, while a consistent bias was absent in temporal pole and prefrontal cortex. A subset of color-biased and object-biased regions defined with an independent fMRI localizer experiment were selective for incongruent objects. Within these regions, voxels most selective for colors or objects were largely separate from voxels most selective for incongruency, (median overlap 20% with color-biased regions, 38% with object-biased regions). These results show that extrastriate retinotopic and posterior IT cortex are important in the formation of and access of color-shape conjunctions.