Here is a description from HCD Research, which operates MediaCurves, about how its surveys are conducted:

HCD samples from a large national database of consumers. The database is built through direct mail and e-mail solicitations inviting people to participate in online communication-research studies.

Panelists are screened to determine their voter-registration status, party affiliation, and pertinent demographic information.

As participants watch excerpts from speeches or other videos on their computer, they use their mouse to indicate levels of agreement, approval, or believability by moving it from left to right on a continuum. Their responses are recorded in quarter-second intervals, and the mean of all responses is reported in the form of curves, which indicate levels of believability for different segments of voters.

During the testing process, respondents are also asked a battery of pre- and post-viewing questions, which are compared to determine if their attitudes have changed as a result of watching the talk show segment or speech.

NOTE: Respondents are paid a nominal honorarium for participating in surveys. For information about becoming a survey respondent, visit the MediaCurves Web site.