Pups between the ages of 9–12 weeks who were permitted to observe their narcotics-detecting mothers at work generally proved more capable at learning the same skills at six months of age than control puppies the same age who were not previously allowed to watch their mothers working. A 2001 study recorded the behaviour of dogs in detour tests, in which a favorite toy or food was placed behind a V-shaped fence. The demonstration of the detour by humans significantly improved the dogs' performance in the trials. The experiments showed that dogs are able to rely on information provided by human action when confronted with a new task. Significantly, they did not copy the exact path of the human demonstrator, but adopted the detour behavior shown by humans to reach their goal. A 1977 experiment by Adler and Adler found that puppies who watched other puppies learn to pull a food cart into their cages by an attached ribbon proved considerably faster at the task when later given the opportunity themselves. At 38 days of age, the demonstrator puppies took an average of 697 seconds to succeed, while the observers succeeded in an average of 9 seconds.