Abstract
Categorization is a process by which the brain assigns meaning to sensory stimuli. Through experience, we learn to group stimuli into categories, such as ‘chair’, ‘table’ and ‘vehicle’, which are critical for rapidly and appropriately selecting behavioural responses1,2. Although much is known about the neural representation of simple visual stimulus features (for example, orientation, direction and colour), relatively little is known about how the brain learns and encodes the meaning of stimuli. We trained monkeys to classify 360° of visual motion directions into two discrete categories, and compared neuronal activity in the lateral intraparietal (LIP) and middle temporal (MT) areas, two interconnected brain regions3 known to be involved in visual motion processing4,5,6. Here we show that neurons in LIP—an area known to be centrally involved in visuo-spatial attention7,8,9, motor planning10,11,12,13 and decision-making14,15,16—robustly reflect the category of motion direction as a result of learning. The activity of LIP neurons encoded directions of motion according to their category membership, and that encoding shifted after the monkeys were retrained to group the same stimuli into two new categories. In contrast, neurons in area MT were strongly direction selective but carried little, if any, explicit category information. This indicates that LIP might be an important nexus for the transformation of visual direction selectivity to more abstract representations that encode the behavioural relevance, or meaning, of stimuli.
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Acknowledgements
We thank J. Ditterich, A. Fanini, V. Ferrera, J. Fitzgerald, C. Freedman, T. Herrington, M. Histed, G. Maimon, E. Miller, C. Pack, C. Padoa-Schioppa, A. Seitz and J. Wallis for comments, help and discussions, and K. Irwin, T. Lafratta and J. LeBlanc for technical assistance. This work was supported by the National Eye Institute (NEI) and the McKnight Endowment Fund for Neuroscience, and a Kirschstein postdoctoral National Research Service Award from the NEI to D.J.F. Author Contributions D.J.F. performed all aspects of this study including the experimental design, data collection and analysis, and writing the manuscript. J.A.A. assisted in experimental design, data analysis and manuscript preparation.
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Freedman, D., Assad, J. Experience-dependent representation of visual categories in parietal cortex. Nature 443, 85–88 (2006). https://doi.org/10.1038/nature05078
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DOI: https://doi.org/10.1038/nature05078
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