title: A horse's eye view: size and shape discrimination compared with other mammals.
abstract: Mammals have adapted to a variety of natural environments from underwater to aerial and these different adaptations have affected their specific perceptive and cognitive abilities. This study used a computer-controlled touchscreen system to examine the visual discrimination abilities of horses, particularly regarding size and shape, and compared the results with those from chimpanzee, human and dolphin studies. Horses were able to discriminate a difference of 14% in circle size but showed worse discrimination thresholds than chimpanzees and humans; these differences cannot be explained by visual acuity. Furthermore, the present findings indicate that all species use length cues rather than area cues to discriminate size. In terms of shape discrimination, horses exhibited perceptual similarities among shapes with curvatures, vertical/horizontal lines and diagonal lines, and the relative contributions of each feature to perceptual similarity in horses differed from those for chimpanzees, humans and dolphins. Horses pay more attention to local components than to global shapes.
authors.affiliation: Primate Research Institute, Kyoto University, Inuyama, 484-8506, Japan tomonaga.masaki.4m@kyoto-u.ac.jp.
authors.forename: Masaki
authors.initials: M
authors.lastname: Tomonaga
authors.affiliation: Horseman Kakamigahara, Kakamigahara, 509-0145, Japan.
authors.forename: Kiyonori
authors.initials: K
authors.lastname: Kumazaki
authors.affiliation: Ecole Nationale Supérieure d'Agronomie et des Industries Alimentaires, 54505, Vandœuvre-lès-Nancy, France.
authors.forename: Florine
authors.initials: F
authors.lastname: Camus
authors.affiliation: L'institut du Cheval et de l'Équitation Portugaise, 93600, Aulnay-sous-Bois, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Nicod
authors.affiliation: L'institut du Cheval et de l'Équitation Portugaise, 93600, Aulnay-sous-Bois, France Institute National de la Recherche Agronomique, 75338, Paris, France Université Paris III Sorbonne Nouvelle, 75231, Paris, France.
authors.forename: Carlos
authors.initials: C
authors.lastname: Pereira
authors.affiliation: Primate Research Institute, Kyoto University, Inuyama, 484-8506, Japan.
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Matsuzawa
mesh_terms: D000818:Animals; D004192:Discrimination, Psychological / Q000502:physiology*; D005556:Form Perception / Q000502:physiology*; D006736:Horses / Q000502:physiology*; D006801:Humans; D002679:Pan troglodytes; D012858:Size Perception / Q000502:physiology*; D014792:Visual Acuity
keywords: comparative cognition; horses; visual perception