Some people had asked in our last prenatal class about why it isn't recommended to allow television for kids under the age of two. As someone who likes to research this kind of stuff I looked up what the general Internet had to say on the topic and forwarded them to my classmates in case anyone else was interested.
This guideline is from 1999 (both in Canada and the US). They are likely to be revised in the near future to distinguish between "verbal" and "non-verbal" infants rather than having an arbitrary age recommendation.
Essentially the conclusion seems to be that in the very early stages of a child's life direct interaction with others is critical to the proper development of their brains.