Learning to discriminate between shapes generalizes to novel stimuli in North American river otters (Lontra...

Perceptual categorization is grouping objects based on similar physical features. Otters may use categorization to classify predators, prey, and conspecifics. This study was the first to examine whether North American river otters (Lontra canadensis) are capable of perceptual categorization. Previously, otters at the Seneca Park Zoo were trained to discriminate between a circle and an equilateral triangle in a two-alternative forced-choice task. In the present study, these otters were presented with novel geometric shapes (e.g., an oval and a right triangle) in Experiment 1 and novel drawings of real-world objects (e.g., a tomato and a tent) in Experiment 2 that could be classified into the circle or triangle category. Two otters performed significantly better than chance during Experiment 1 on subsets of the novel test stimuli. In Experiment 2, one otter was able to categorize drawings of real-world objects into two shape categories of circles and triangles, but only when the triangle-like stimuli were composed of straight lines, not when stimuli were composed of curved lines. The results from both experiments suggest that line type (straight vs. curved) and symmetry may have been salient features for the otters. It appears that otters have the ability to perceptually categorize two-dimensional shapes and line drawings, though further research with additional subjects and different stimuli is needed. Better understanding this ability in otters can expand our knowledge of categorization behavior in a variety of nonhuman animals. (PsycInfo Database Record (c) 2026 APA, all rights reserved).