A joint study conducted by search marketing firms Enquiro and eye tracking firm Eyetools examined the eye movements of web surfers viewing Google search result pages.
They found that the first 3 listings get 100% attention, sites ranked 6th gets 50% attention while sites ranked 8th get only 30% attention. Anything below that is almost ignored.
The sponsored links ranked 1st and 2nd get 50% and 40% attention respectively while anything after 4th is almost not seen by the user.
A screenshot of viewing patterns can be seen here.