The average attention span of a human?

This infographic suggests the average attention span of a human is now less than that of a gold fish (that is, less than 9 seconds).
Is this true?
Humans can show marked focus on the things that interest them. We read long articles. We devote hours to commenting on various topics that arouse our passions. We binge-watch whole seasons of favorite TV shows on Netflix. We spend three hours in a dark movie theater. We can be intensely focused on the statistics related to our favorite sports team.
So we have a long attention span for what interests us.
But our filter speed for what interests us has become intensely short.
Our “filter” is what determines whether an individual item will probably interest us or not. So much information is coming at us, we can’t afford to spend even 12 seconds on each individual item as we did in years gone past. By shrinking filter time to 8 seconds, we can handle 33% more items (and even this may not be enough).
8 seconds may even be magnanimous. It’s about what I give to an article once I have clicked into it. The individual Tweet or Facebook post doesn’t typically get even that much – maybe half a second.
We can bemoan this situation. But we have to realize the idea we are promoting doesn’t automatically deserve attention. The communication of an idea must earn attention – it must survive the filter. This can be done in several ways:
1. We can more concisely and vividly write the “headline” that leads to the link. This is part of the idea between Growth Hacking & Made to Stick.
2. We can build a tribe of people who know us and trust us and will give our content a longer look. This is part of the idea behind Tribes.
3. We can get a lot of people to recommend the article. This builds on Tribes and is the idea behind Viral campaigns.
4. We can buy advertising around keywords that indicate people are searching for the idea. This is the idea behind Google Adwords.
5. We can structure the content of our idea in a way that Google & other search engines find it, and promote it. This is the idea behind SEO.
I’m sure there are other ideas. What strategies do you use?