Discrimination of small intervals and objects by raccoons

Abstract

Two experiments were conducted to determine the visual discrimination abilities of raccoons in regard to materials used in testing in the Klüver-Wisconsin General Test Apparatus. Knowledge of these abilities is prerequisite to obtaining behavioural comparisons between raccoons and other species, particularly primates, which have been extensively tested using this apparatus.Separation discrimination was tested by a chain pulling method, wherein the animals were required to draw in that one of two chains to which a food cup was attached. The distance between the chains was varied systematically. At a distance of 14″, raccoons discriminated intervals as small as 14″. However, there was a progressive decrement in discrimination accuracy for intervals smaller than 3″.The second experiment investigated the discrimination of very small objects. After a discrimination between two objects of 1″ maximum linear extent was learned, replications of these objects having a maximum linear extent of 12″, 14″, and 18″ were presented. At a distance of five inches, all objects were successfully discriminated by all subjects, with no apparent differences from one size to another. It was concluded that raccoons are capable of discriminating visually the smallest sizes of objects that could be used practicably in this situation. Furthermore, discrimination of all sizes of objects improved with experience.