Prof Daniel Mills has released result of research into the factors that affect a dog's obedience to commands. In the research the team trained dogs to respond to verbal and visual cues, and then tested them under variable conditions.
While the dogs responded fairly equally to either verbal or visual signals alone, when the researchers gave a verbal 'left' cue with a 'right' hand signal the dogs usually followed the hand pointing right, and ignored the verbal 'left'. If the researcher looked to the right as they pointed right the results were even more consistent, suggesting that dogs read the whole body, and don't just follow hands.
When the dogs reliably responded to the verbal cue alone, the researchers changed the cue word slightly; using 'chit' and 'sik' in place of 'sit', for example. The dogs did not respond as well to the variations, suggesting that slight differences in the pronunciation of words affect dog's understanding of them.
In further experiments, Mills and his team found that dog's rate of obedience dropped if the handler sat, or wore sunglasses, and if the command came from a tape recorder behind the handler, or if the handler was looking away from the dog. And with dogs that would come reliably when called from behind a screen, the level of obedience dropped significantly if commands were uttered in an angry or gloomy tone.
Of course, much research time and government money could have been saved if they had just asked agility competitors about this.