Spencer Loggia^1,2, James Cavanaugh¹, Bevil Conway^1,3; ¹National Eye Institute, ²Brown University, ³National Institute of Mental Health

Object concepts are cognitive tools that reflect an interaction of features, such as shape, color, and value. A “Banana” is a yellow crescent that promises sweet nutrition. The neural computations by which visual input allows object concepts to be learned and deployed are poorly understood. A challenge is that concepts differ between people, and likelihood functions and priors are not precisely known. Monkeys could be a useful model – their visual diet can be curated, and tools exist to probe mechanisms at cellular resolution. But do monkeys form object concepts? We developed and deployed a foraging paradigm using in-cage touchscreens to address this question. We used an innovative color-shape space to define 2-dimensional objects and evaluated behavioral data using a reinforcement-learning framework. Smooth maps of the objects’ reward values and frequencies of presentation were defined over a circular parameter space. Importantly, the paradigm was constructed so that the resulting marginal reward values for color and shape are useful but not sufficient for determining reward, color-shape contingencies are also informative. Four macaques performed a four-alternate-choice task daily for two years, achieving near-optimal performance. At plateau performance, the monkeys performed significantly better than a model that linearly integrates separable color and shape information (paired t-test, p<1e-8) - they can exploit interactions between shapes and colors. Moreover, the monkeys assigned higher value to exemplars further from reward boundaries (linear regression; p=0.0), predicted if they employ a cognitive model of object concepts. A Recurrent Neural Network uncovered the process through which the animals acquired concepts. The RNN suggests that the monkeys’ default object concept is warm-and-blobby, and the reward marginals are learned before contingencies. These results show that monkeys, like humans, exploit object concepts that emerge as conjunctions of color and shape, conditioned predominantly by reward and less so by frequency of exposure.