Like humans, monkeys naturally associate members of their «in - group» with positive stimuli such as fruits, and out - group members with negative stimuli such as spiders. (newscientist.com)
Obviously, like most creatures, dogs will seek to avoid negative stimulus (6) and their intelligence allows them to pair specific actions with the initiation of that stimulus. (topdogtips.com)
Some also argue that shock collars are not an effective method of training because they provide negative stimuli, and positive stimuli are more effective when training a dog. (wideopenpets.com)