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Chaser has the largest tested memory of any non-human animal. She knows over 1,200 words, and has over 1,000 toys that she knows by name and can fetch on command!
How Chaser learned all these words has a lot to do with her former trainer, John W. Pilley. Pilley, an emeritus professor of psychology at Wofford College, specialized in classical and operant conditioning. He soon became interested in animal behavior, and began working with Chaser in 2004. Pilley started teaching Chaser to identify her toys by name, and the rest is history.
Chaser is a Border Collie, a breed considered to be highly intelligent. Border Collies are working dogs, and this, combined with their intelligence, means they need mental stimulation or they can become destructive and neurotic. This makes them the ideal dogs to teach new ideas and tasks, as they not only want but need to do work.
While deciding how to teach Chaser, Pilley observed that Border Collies had historically been able to learn the individual names of different sheep. Pilley decided the best way to teach Chaser would be to work with her natural instincts. He began teaching her words using a technique called "Match to Sample," where he would put down two objects, like a Frisbee and a rope, and then throw another Frisbee and ask Chaser to fetch the Frisbee. Chaser would recognize that the two Frisbees looked similarly, and thus would learn the word for Frisbee.
As time went on, Chaser was able to learn the names of over 1,000 toys, which, Pilley theorized, mimicked a farmer's herd of sheep in Chaser's mind. To learn names of new toys, Pilley would set down toys that Chaser already knew, and add a new toy. Pilley would then ask Chaser to fetch the toy with the new name. Chaser would go to her toys and be able to infer which toy was new based on the fact that she knew the names of all the other toys. This process is called "inferential reasoning by exclusion."
In addition to knowing the names of her toys, Chaser can also play "hot and cold" to find a toy, and understands not only nouns but also many verbs, adjectives, and prepositions. Many have observed that Chaser is not just memorizing things, but also actively thinking and processing ideas when she is presented with them.
Pilley wrote a book called Chaser: Unlocking the Genius of the Dog Who Knows a Thousand Words. Pilley passed away in July of 2018, but his daughters now care for and continue to work with Chaser. They are currently writing another book, A World of Chasers.
You can learn more about Chaser and see what she's up to on her Facebook page. Good girl, Chaser!