by Geordie Lancaster

Category learning is an important ability that enables organisms to organize their environment in ways that reduce the amount of cognitive strain of everyday stimuli. The two necessary components of categorization are generalization and discrimination. This involves being able to include many objects in to a category while excluding others. A comprehensive review of the research that has been done on category learning in non-human animals has shown that many animals, including pigeons, dogs, primates and horses, have the ability to categorize stimuli. Since 1964, when Herrnstein and Loveland published their study on the ability of pigeons to categorize stimuli, many researchers have studied category learning in non-human animals. The development of category learning, however, is one area that has not been studied to a great extent. Additionally, the research that has been completed on the development of category learning focuses mainly on monkeys.

The horse has not been studied as much as other species in the area of category learning, and the development of category learning has been neglected to date. The purpose of the present study is to study two age groups of horses, 3 months and 15 months old, in an attempt to explore the development of category learning in horses.

Three 3 month old horses and three 15 month old horses were trained to respond to two categories of computer generated shapes: plus signs and ellipses. The stimuli were presented one at a time in an apparatus with two response panels. One of the categories was associated with one of the response panels while the other category was associated with the other response panel. During training some of the horses showed evidence of category learning, and during testing two of the horses performed above the criterion indicating they were able to categorize the stimuli. The horses were also tested with novel stimuli during the testing phase to ensure those who met the criteria had, in fact, learned the categories. One of the horses that did meet the criteria during the testing phase did not perform better than chance for the new stimuli, suggesting that it may have memorized the training stimuli. One of the horses did perform equally for the new and old stimuli, indicating that it did learn the categories.

The younger horses were not able to learn the categorizing task; however, one of the older horses did learn the task, while another older horse almost learned the task. These results may indicate that at three months, horses have not yet developed the ability to categorize stimuli. Small sample size and individual variability, however, prevents definite conclusions.