Before revision:  The time series were successfully fitted by a low dimensional model that integrates two basic collective behaviors: an imitative component, and a fading of collective attention to the institutional regulation. We show that the natural scale over which collective attention fades is inversely proportional to the frequency of use of the verbs .
After revision:  The time series were successfully fitted by a low dimensional model that integrates an imitative and a novelty component. The model reveals that the temporal scale over which collective attention fades is inversely proportional to the frequency of use of the verbs .