Le chien aux 200 mots

The study animal, Rico, is a border collie and was born in December 1994. He lives as a pet with his owners and was reported by them to know the labels of over 200 items, mostly children's toys and balls, which he correctly retrieved upon request. Rico was first introduced to fetching items when he was 10 months of age, when his owners placed three different items in different locations around the flat and asked the dog for one of these items. Rico was rewarded with food or play if he fetched the correct object. He was gradually familiarized with an increasing number of items.

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The first experiment was therefore designed to assess Rico's ability to correctly retrieve his various items under controlled conditions. We randomly assigned the 200 items he was reportedly familiar with to 20 sets of 10 different items each. While the owner waited with the dog in a separate room, the experimenter arranged a set of items in the experimental room and then joined the owner and the dog. Next, the experimenter instructed the owner to request the dog to bring two randomly chosen items (one after the other) from the adjacent room. While Rico searched for the requested item, he could not see the owner or the experimenter. He retrieved a total of 37 out of 40 items correctly (binomial test, P < 0.001). This experiment showed that Rico indeed knew the labels of these items. One may raise the objection that the words may in fact constitute one-word propositions, such as "fetch-the-sock." However, anecdotal evidence suggests that he indeed understands that the words refer to the objects. For instance, he can be instructed to put an item into a box or to bring it to a certain person. More systematic testing will be needed to specify his understanding of entire phrases. In any case, the number of labeled objects is substantially larger than those reported in previous studies with dogs, where subjects were tested with only three to five objects. Rico's "vocabulary size" is comparable to that of language-trained apes, dolphins, sea lions, and parrots.

To assess Rico's ability to fast map, we placed a novel item together with seven familiar items in an adjacent room (total n = 8 items requested in 8 trials). In this so-called identification task, we conducted a total of 10 sessions in which we introduced 10 novel items. In the first trial of a session, the owner always asked Rico to bring a familiar item, and in the second or third trial asked him to bring an item using the novel name. After the completion of a session, Rico was allowed to take a break before another session commenced. Rico retrieved the novel item from the first session on and was overall correct in 7 out of 10 sessions (binomial test, P < 0.001). Apparently, he was able to link the novel word to the novel item based on exclusion learning, either because he knew that the familiar items already had names or because they were not novel. Four weeks after the initial and sole exposure, we assessed Rico's retention of the relation between the novel word and the novel item. In this retention task, we only used those objects that Rico had successfully retrieved in the identification task. In between the identification and the retention task, he had no access to the target items. We placed a target item together with four completely novel and four familiar items in a room (total n = 9 items) and asked him first to bring a familiar item and subsequently (in the second or third trial) to bring the target item. Four weeks after the identification task, he correctly retrieved the target item in 3 out of 6 sessions (P < 0.1). This retrieval rate is comparable to the performance of 3-year-old toddlers.

(Science, 10 juin 2004)