Alan Jacobs in The Hedgehog Review:
Every medium of communication has its own attentional norms. Like all tacit rules that govern behavior, they get violated, but the violators typically act deliberately. For instance, the people who talk aloud in the movie theater typically aren’t ignorant of the norms; they transgress them for the lulz. Human beings are extremely skilled at recognizing and internalizing the norms of any given medium or environment.
Such norms are not set in stone but rather can alter over time. The strict decorum demanded of classical music audiences was codified in the early twentieth century, largely through the influence of Gustav Mahler. By contrast, Haydn and Mozart had to put up with noisy audiences, and indeed rarely began a symphonic piece quietly because if they had done so no one would have known that the music had started. Similarly, it was common in the Middle Ages for churchgoers to chat through most of Mass and even play cards, listening with one ear to the bells that would alert them when their attention was required. (Even the more overtly pious would often pray the rosary as the priest said the Mass, again relying on the bells as a notification system.) Still, despite changes that inevitably occur over the long term, at any given moment in time most people know what the attentional norms are for any social endeavor they participate in.
It has been interesting to watch over the last two pandemic years as the norms associated with videoconferencing have coalesced.