I had the pleasure of speaking at Interact London in October 2014. I presented an updated version of this talk, which I originally gave at IA Summit earlier in the spring. The talk is based on content from my book, Understanding Context. You can read more about it at http://contextbook.com.
In this version, I have updated the way I'm talking about how language works as environment: instead of 'semantic affordance' I'm now calling it 'semantic function.' (Which is in keeping with how it's now being described in the book.)