Fig. 2: Variation of the language categories over time.

The number of recorded infections in the U.S. (A), and the average gradient (i.e., instantaneous variation) of all the language categories (B). There were three contagion waves in the year (shaded areas in A) and, for each wave, there were peaks in the gradient (marked with circles in B), which identify change-points, that is, periods in which the use of language considerably changed.