Learning is…10 minutes long
According to John Medina's excellent book "Brain Rules" the optimal human attention span is around 10 minutes.
When delivering classes he stated, "I needed to do something after the 601 second to "buy" another 10 minutes." A sixty minute class was essentially six 10-minute modules. The end of each required a pause and the beginning of the next with a "hook" or intro to buy the next 10 minutes. (He was awarded the Hoechst Marion Rousell Teacher of the Year for his efforts.)
The same principle applies in other types of media. Broadcast television is usually in 10 minutes increments, broken up by commercial breaks. News show interviews, magazine type reports and other media often follow the same rule.
The golden rule for learning videos we created was NEVER longer than 10 minutes. It's long enough to make the point and short enough to focus attention. But with the use of Facebook and Twitter is 10 minutes even too long today?