Adaptive testing of the critical features in 2D-shape discrimination by pigeons and starlings.

An innovative adaptive discrimination procedure examined how two bird species, pigeons and starlings, recognize and discriminate two-dimensional (2D) visual shapes. Prior results suggest a comparative divergence between mammals and birds in their relative reliance on vertices versus line segments to mediate discrimination. To address this potentially important difference, four pigeons and five starlings were tested with a square versus triangle discrimination in two experiments. An adaptive genetic algorithm guided the selection and organization of the training and test stimuli. Both species showed considerable flexibility in accurately selecting triangles despite wide variation in stimulus appearance and location. Most critically, Experiment 2 revealed that both bird species relied more on the figures' vertices during successful discrimination than their connecting line segments. This reliance was revealed by both traditional accuracy differences using contour-deleted displays and genetic algorithm-based shifts in "gene values" caused by the birds' selection. These results, in contrast to previous findings, indicate that mammals and birds likely converge in their reliance on vertices as a highly critical feature in visual shape discrimination. (PsycInfo Database Record (c) 2021 APA, all rights reserved).