A data gathering system includes a plurality of remote units which are controlled from a central location. Each of the remote units is attached to a television receiver which is generally but not necessarily attached to a cable system. Each of the remote units can function to determine which of several TV modes is in use as well as to store TV channel selector data, data from an optical input device, and/or data input by viewers representative of the composition of the viewing audience. The data is stored for either later collection by a portable data collector, or for direct transmission to the central location. A video message for a TV viewer, such as a survey, may be transmitted from the central location and stored at the remote units, for later display on the TV receiver associated with the remote units. Substitution of alternate programming information may also be achieved by the central control point on selected of the remote units.