Early research by Triplett involved motor tasks like bicycling and winding fishing reels, employing a co-action manipulation. Triplett observed the phenomenon of social facilitation, that is the improvement of performance. However, later researchers found that the presence of others sometimes worsened performance. This was very confusing. It is the mere presence of other co-specifics that does this, which accomodates the animal data.
Arousal enhances the probability of emitting dominant responses.
There is improved task performance if the dominant responses are correct, worsened if incorrect. Through learning co-specifics elevate arousal because we come to associate them with rewards and punishments. This explains the effects seen in animals. In humans social facilitation would primarily occur when the situation is compatitive or evaluative. Cottrell blindfolded spectators and found no effects on performers.