The new institutional economics has recently developed the idea that the institutional environment can have an impact on economic actors' mental perceptions, and reciprocally, that these perceptions can impact on the institutional environment. This latter point seems particularly relevant in the field of economic organisations participation in the political making process. Nevertheless the empirical description of this role of mental perceptions in the political behaviour had not been made clearly. To contribute to this empirical description we lead a comparative study of 4 farm sectors in Costa Rica, based on a dynamic approach of mental perceptions in relation with the institutional change occurring during the liberalisation process. We carry out a statistical analysis of mental perceptions through a textual analysis of actors perceptions of the institutional change, leading to two main conclusions. Firstly we provide an empirical confirmation that mental models are influenced by specific institutional environments and lead to different strategies regarding the participation to the political making process. Secondly, we show that when an exogenous change occurs in the institutional environment, the mental models existing before the change can persist and lead to inefficient behaviours. This can partly explain part of the difficulties some sectors to lead efficient political activity that ensures their survival in a liberalized environment.