February 21, 2009

A study of three horses has added weight to the belief of many owners that their equine companions have long memories.

The study, led by Equine Research Foundation co-director Evelyn Hanggi, has just been published in the January edition of the journal Animal Cognition.

Dr Hanggi and fellow researcher Jerry Ingersoll took three horses that had performed cognitive tasks in research dating back several years. The tasks had involved discrimination learning, categorisation, and concept use.

The horses were tested to evaluate their long-term memory in three experiments.

In addition, the reseachers used LCD displays for the first time with the horses in presenting some of the images at the centre of the experiments.

The first experiment tested long-term memory for discrimination learning that had originally occurred with the horses six years earlier.

Five sets of stimuli were used and the two horses tested showed no decrease in selection performance on four of the sets. However, both horses did score below chance on one set.

Experiment two examined long-term categorisation recall 10 years after horses had demonstrated the ability to make stimulus selections based on shared characteristics within a given category.

The horse tested for long-term memory after the decade-long interval immediately and consistently applied the previously learned categorisation rule to not only familiar but also novel sets of stimuli.

The third experiment tested another horse for long-term memory for a relative size concept - something it had been trained to do for research years earlier.

"More than seven years later and without further training, this horse reliably applied the previously established size concept to both familiar and novel sets of stimuli," the researchers said.

"These findings are the first reports of long-term categorical and conceptual memory in horses and are consistent with observations of domestic and wild horses, which indicate that behavioural and ecological events may be remembered for long periods of time.

"These studies also demonstrate the adaptive nature of horses with regard to their ability to generalise over several different testing conditions."

Long-term memory for categories and concepts in horses (Equus caballus). Authors Hanggi EB, Ingersoll JF; Equine Research Foundation, P.O. Box 1900, Aptos, CA, 95001, USA, EquiResF@aol.com.
Source: Animal Cognition 2009 Jan 16.