Nielsen families are volunteers to the Nielsen ratings group. By the 31st century, they are capable of monitoring eyeball focus on these subjects, by inserting large tubes into them as well as having a readout on their foreheads. Subjects also include animals.
These families were part of the argument to keep Bender on All My Circuits by the president of the network, since eyeball focus was up 90% during the time Bender was on the screen. This was despite Bender's inferior coma acting abilities.