Abstract: Most of the current researches on trust and cooperation have been studied from the perspective of behavior or from the perspective of outcome. The former takes the trust equal to the individual cooperative behavior, and the later abstracts the trust as an impact factor of player's expected outcome. However, with the development of cognitive psychology, more and more scholars have found that trust belongs to psychological cognitive process essentially, and trust can lead to cooperation, but cooperation cannot explain the degree of trust completely. Hence, no matter studying the trust and cooperation from the perspective of behavior or from the perspective of outcome cannot match our current comprehension of the trust. Against this background, trust is portrayed from the cognitive perspective by the cognitive psychology and the trust is regarded as a faith that opponent will choose cooperation in the interaction.
Dilemma game is taken as example and faith learning and updating is used to portray trust. By using dynamic trust forecasting cognitive model, equilibrium in one-time prisoner's dilemma game, finitely repeated prisoner's dilemma game and infinitely repeated prisoner's dilemma game have been studied, and thus the evolution of cooperation in short-term relationship, the medium-term relationship and long-term relationship have been observed. According to the results, in short-term relationship and medium-term relationship, when the trust degree exceeds a critical value, cooperating with opponents becomes the dominant strategy of the players, and cooperation turns to be the equilibrium of the game system. When players are in long-term relationship, whether the current round satisfaction degree, historical direct trust degree, direct trust degree, or indirect trust degree, and the active degree of the players and other factors have a certain impact on their cooperative behavior at equilibrium. At last, a numerical example has proved this study.
According to our study, the generation and maintenance of cooperation can be promoted by improving trust degree between individuals. Generally speaking, approaches to enhance the trust degree between individuals are as follows:increasing indirect trust degree by establishing and maintaining a reputation, improving satisfaction degree by improving personal performance in each interaction. For those individuals who already have relatively good reputation, it is wise to enhance their active degree of the social system to endow more weight to their direct trust. In all, This study can help us understand the impact of trust on cooperation from the perspective of cognitive psychology.

Key words: cognitive modeling, over all trust degree, direct trust degree, indirect trust degree