Abstract
In their natural environment, animals often make decisions based on abstract relationships among multiple stimulus representations. Humans and other primates can determine not only whether a sensory stimulus differs from a remembered sensory representation, but also how they differ along a particular dimension. However, much remains unknown about how such relative comparisons are made, and which species share this capacity, in part because most studies of sensory-guided decision making have utilized instrumental tasks in which choices are based on very simple stimulus–response associations. Here, we used a two-stimulus-interval discrimination task to test whether rats could determine how two sequentially presented stimuli were related along the dimension of odor quality (i.e., what the stimulus smells like). At a central port, rats sampled and compared two odor mixtures that consisted of spearmint and caraway in different ratios, separated by a 2–4-s interval, and then entered the left or right reward port. Water was delivered at the left if the first mixture consisted of more spearmint than the second did, and at the right otherwise. We found that the difference in mixture ratio predicted choice accuracy. Control experiments suggest that rats were indeed basing their choices on a comparison of odor quality across mixtures and were not using associative strategies. This study is the first demonstration of the use of a sequential “more than versus less than” rule in rats and provides a well-controlled paradigm for studying abstract comparisons in a rodent model system.
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Acknowledgments
We thank the employees of the Center for Comparative Medicine for the care they provided for the rats. We thank Drs. Carlos Brody, Andrew Barron, Elizabeth Stubblefield, John Thompson, and Nicolas Busquet for their invaluable comments on an initial draft of the manuscript. We thank Jamie Costabile for technical support during this work. This work was supported by the National Institutes of Health, grant 5T32NS007083 (Clint Perry); and the Boettcher Foundation Webb-Waring Biomedical Research Award (Gidon Felsen).
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The authors declare that they have no conflict of interest.
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The experiments comply with the current laws of the country in which experiments were performed.
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Perry, C., Felsen, G. Rats can make relative perceptual judgments about sequential stimuli. Anim Cogn 15, 473–481 (2012). https://doi.org/10.1007/s10071-012-0471-4
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DOI: https://doi.org/10.1007/s10071-012-0471-4