alt Hacker NewsSounds like they took a cue from Sesame Street:
> p8: "A child watching television under normal conditions is subject to frequent interruptions and distractions. The TV must vie for his attention. In order to simulate this condition, we decided to program distractions into the laboratory situation... Slides could be used to fill the slide tray and they could be projected automatically, at regular intervals, onto a screen similar to that of the television set. The carousel projector allows the viewer to choose three exposure times. The 7.45 second interval proved most satisfactory with the preschool children.
THE FIRST YEAR OF SESAME STREET: THE FORMATIVE RESEARCH https://files.eric.ed.gov/fulltext/ED047822.pdf
And nowadays we think of Sesame Street as wholesome compared to today's content. They may have optimised attention but they were delivering positive-value content. That's not the case any more.