divided into three groups. Group A received an electric shock when the dogs touched the prey (a rabbit dummy fixed to a motion device). Group H received a shock when they did not obey a previously trained recall command during hunting. Dogs in group R received the electric shock arbitrarily, i.e. the shock was administered unpredictably and out of context. Group A did not show a significant rise in stress-indicating salivary cortisol levels, while group R and group H did show a significant rise. This led to the conclusion that animals which were able to clearly associate the electric stimulus with their action, i.e. touching the prey, and consequently were able to predict and control the stressor, did not show considerable or persistent stress indicators, while animals that were not able to control the situation to avoid the shock did show significant stress. In 2004 a study was published that was based on the observation of a variety of breeds trained for protection work using shock collars, which showed that although electronically trained dogs can excel as guard dogs, their behavior toward humans and work circumstances changed, often indicating heightened uncertainty and reactivity. Lindsay says of this study, "Schilder and Van der Borg (2004) have published a report of disturbing findings regarding the short-term and long- term effects of shock used in the context of working dogs that is destined to become a source of significant controversy ... The absence of reduced drive or behavioral suppression with respect to critical activities associated with shock (e.g., bite work) makes one skeptical about the lasting adverse effects the authors claim to document. Although they offer no substantive evidence of trauma or harm to dogs, they provide loads of speculation, anecdotes, insinuations of gender and educational inadequacies, and derogatory comments regarding the motivation and competence of IPO trainers in its place." However, newer studies such as those by Herron et alia suggest that aversives such as shock, as well as lesser aversives such as yelling, do come with a risk of increasing behavior problems including aggression. Model-rival training Based on the principles of social learning, model-rival training uses a model, or a rival for attention, to demonstrate the desired behavior. The method was used by Irene Pepperberg to train Alex the African Grey Parrot to label a large number of objects. McKinley and Young undertook a pilot study on the applicability of a