In both cases, requests are composed either of single words or short phrases which may be functionally equivalent to single words, ,. ĭogs' responsiveness to words has been examined either under action request conditions (dogs are required to perform an action when prompted by a verbal command: “sit”, “roll”, “give paw”, “fetch”) object request conditions (they are trained to react selectively to one of several objects according to a verbal command such as “fetch the ball, the teddy, the newspaper, etc.”). Betsy, another family trained border collie, fetched any object in a set of hundreds when prompted through verbal labels, and could use photographs as sufficient information about items to be searched for more recently, Chaser, trained over a period of three years, was able to learn and retain the names of more than a thousand objects and to use words representing object categories. A critical evaluation of an interpretation in terms of fast mapping has been proposed, though. A high level of competence in word comprehension has been demonstrated in some dogs: Rico, a border collie, was able to discriminate dozens of words and showed a “fast-mapping” performance similar to children's, that is, the capacity of attributing, by exclusion, a new word to an object never seen before. Early, , and more recent investigations examined dogs' capacity to discriminate words associated with different objects, places and performances, with an interest in referential knowledge. We know that word discrimination may be affected by the human sender's attentional status and appearance, , by nonverbal signals that go along with words and by small changes in the phoneme composition of words. Owners report that their dogs have a very developed understanding of words, and verbal commands are widely and successfully used by dog trainers to induce and control a variety of behaviors. Human language constitutes another very common source of signals to which dogs appear to be remarkably responsive, but which is still insufficiently investigated. A large amount of research has shown that they can, very early in ontogeny, successfully use social cues such as pointing or gazing or body posture to locate hidden food.

Dogs are endowed with a special ability to understand human signals.

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