Attention span

A person's attention span is the period of time during which they can remain focused on a goal or objective.

Attention spans vary enormously and are affected by individual differences, age, motivation, present psychological state and a host of other factors.

In order to retain our students' attention it is necessary to change the focus of the lesson periodically&mdash;perhaps every twenty minutes.

Regarding PowerPoint (PPT) presentations, etc., while not specifically mentioning PPT, an MIT "how-to" presentation states that attention span for a slide is 8 seconds.