Which of the following is a principal task of the usability tester role?

The usability tester, often synonymous with the usability test moderator in practice, is primarily responsible for interacting directly with the test participants during the usability testing sessions. This role includes communicating with participants to guide them through test tasks, answering questions without leading responses, and ensuring the session runs smoothly. Effective communication is essential to facilitate participant comfort, elicit genuine user behaviors, and capture accurate usability data.

Performing the pre-session briefing (Option A) may be done by the usability tester but is often a shared responsibility or part of test facilitation protocols. Discussing findings (Option C) typically falls to analysts or usability experts after testing sessions are completed and data analyzed. Defining testing tasks (Option D) is usually done by test designers or analysts during test planning, not during the test execution.

Therefore, communicating with test participants during testing is a core, principal task of the usability tester role.