I don't know that once adulthood is reached there is any active intelligence deterioration, but I do think a case can be made for the lack of critical thought generated by the easy consumption pushed forward by major television outlets. I use TV to watch Vince Carter dunk highlights and music videos. :) Hikaru Takeuchi has more in this article: http://www.scientificamerican.com/article/does-tv-rot-your-brain/