Chaser, the Border Collie Who Learned 1,022 Words

A border collie named Chaser learned the names of 1,022 different toys, and she remembered every one. Over three years of daily lessons in Spartanburg, South Carolina, psychologist John Pilley taught her a vocabulary larger than that of a typical two-year-old child, and in 2011 he published the results in the journal Behavioural Processes.

Pilley was a retired psychology professor at Wofford College when his wife Sally gave him a black-and-white border collie puppy in 2004, shortly before his 76th birthday. According to PBS NOVA, researchers at the time were excited about Rico, a dog in Germany who knew the names of about 200 items. Pilley suspected a dog could go much further.

Rico himself had made headlines in Science in 2004. Juliane Kaminski and colleagues at the Max Planck Institute showed that he could pick out a new toy by exclusion: asked for an unfamiliar name, he fetched the one object he had never seen before. Children do the same thing, a skill psychologists call fast mapping.

Pilley's method was patient and playful. The New York Times reported that he trained Chaser four to five hours a day, showing her an object, saying its name up to 40 times, then hiding it and asking her to find it. Her collection eventually held 800 cloth animals, 116 balls, 26 Frisbees and an assortment of plastic toys, each with its own name, from a dolphin called porpoise to a monkey called Uncle Fuzz.

The tests were strict. In the 2011 paper, written with Alliston Reid, the toys were drawn at random and placed in another room, so Pilley could not guide her with glances or gestures. Chaser had to go out, find the named object among others and bring it back. The study also showed that she understood names as labels for things, not as commands. She could take, paw or nose a named toy, combining three actions with three names in random pairs.

She learned categories as well. Chaser grasped that ball meant any of her balls while each one still had its own proper name, the kind of one-to-many mapping children master early. Like Rico, she could also infer the name of a brand-new toy because it was the only unfamiliar object in the pile. A 2013 study in Learning and Motivation went further, testing whether she followed short sentences that combined a verb with two objects.

On 60 Minutes, Pilley told Anderson Cooper that in every test she correctly identified 95 percent or more of the toys. Duke University anthropologist Brian Hare described her on the show as possibly the most important dog in modern scientific research, because she learned words in a way that resembles how young children do.

Pilley died on June 17, 2018, and Chaser died of natural causes on July 23, 2019, at the age of 15, a little beyond the usual lifespan of her breed. Wofford College notes that she knew 1,022 nouns and three verbs and was the subject of Pilley's book Chaser: Unlocking the Genius of the Dog Who Knows a Thousand Words. Her story suggests that the gap between how dogs and toddlers learn words is smaller than many scientists once assumed.

Sources: Behavioural Processes (2011); Learning and Motivation (2013); Science (2004); The New York Times; PBS NOVA; Wofford College; CBS News, 60 Minutes. Cover: Border collie chasing a ball on the beach, CC0.jpg).