The efficient markets hypothesis (EMH) requires neither "perfect information dissemination" or "uniformly rational agents".
Here is one well stated version of the EMH:
"The Efficient Market Hypothesis (EMH) essentially says that all known information about investment securities, such as stocks, is already factored into the prices of those securities. Therefore no amount of analysis can give an investor an edge over other investors. EMH does not require that investors be rational; it says that individual investors will act randomly but, as a whole, the market is always "right." In simple terms, "efficient" implies "normal." For example, an unusual reaction to unusual information is normal."[1]
Here is one well stated version of the EMH:
"The Efficient Market Hypothesis (EMH) essentially says that all known information about investment securities, such as stocks, is already factored into the prices of those securities. Therefore no amount of analysis can give an investor an edge over other investors. EMH does not require that investors be rational; it says that individual investors will act randomly but, as a whole, the market is always "right." In simple terms, "efficient" implies "normal." For example, an unusual reaction to unusual information is normal."[1]
[1] http://mutualfunds.about.com/od/mutualfundglossary/a/Efficie...