Color vision in horses (Equus caballus): Deficiencies identified using a pseudoisochromatic plate test.

In the past, equine color vision was tested with stimuli composed either of painted cards or photographic slides or through physiological testing using electroretinogram flicker photometry. Some studies produced similar results, but others did not, demonstrating that there was not yet a definitive answer regarding color vision in horses (Equus caballus). In this study, a pseudoisochromatic plate test--which is highly effective in testing color vision both in small children and in adult humans--was used for the first time on a nonhuman animal. Stimuli consisted of different colored dotted circles set against backgrounds of varying dots. The coloration of the circles corresponded to the visual capabilities of different types of color deficiencies (anomalous trichromacy and dichromacy). Four horses were tested on a 2-choice discrimination task. All horses successfully reached criterion for gray circles and demonstration circles. None of the horses were able to discriminate the protan-deutan plate or the individual protan or deutan plates. However, all were able to discriminate the tritan plate. The results suggest that horses are dichromats with color vision capabilities similar to those of humans with red-green color deficiencies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Kin recognition in captive California sea lions (Zalophus californianus).

Observations of behavior were made of a captive colony of California sea lions (Zalophus californianus) at Sea Life Park, Hawaii. Animals were classified as relatives or nonrelatives, and behavior was categorized as aggressive or affiliative. Mothers interacted in an affiliative manner exclusively with their offspring (1–21 yrs of age). In addition, siblings and half-siblings interacted more with each other than they did with unrelated animals. Females with no relatives in the colony kept primarily to themselves, and when they did interact, it was usually in an aggressive manner. There were very few aggressive interactions between relatives, even during feeding sessions where there was intense competition. Mother–pup bonding and familial relationships in captive California sea lions extend over a number of years and may last a lifetime. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Categorization learning in horses (Equus caballus).

Categorization learning was investigated in 2 horses (Equus caballus). Both horses learned to select a 2-dimensional black stimulus with an open center instead of a filled stimulus in a 2-choice discrimination task. After a criterion of 10 out of 10 correct responses in a random series for 2 consecutive sessions was reached, 15 additional pairs of open-center versus filled stimuli were tested. Each was run to criterion and then incorporated into sessions of randomly mixed problems. Both horses solved the 1st problem by simple pattern discrimination and showed evidence of categorical processing for subsequent problems. New pairs were learned with few or no errors, and correct responses on novel trials were significantly above chance. These results suggest that the horses were making their selections on the basis of shared characteristics with the training stimuli and were using categorization skills in problem solving. (PsycINFO Database Record (c) 2010 APA, all rights reserved)