Data sensing refers to the acquisition of information about an object, subject, or phenomenon using sensor technologies. Today, sensor technologies are able to measure almost any physical quality—including electromagnetic radiation; emitted or reflected light (e.g., infrared light in eye-tracker systems); temperature, acoustic, electric current, or activity (e.g., heart or brain activity); chemical reactions; forces (e.g., pressure and weight); and position measurements (e.g., speed and acceleration). While sensing technologies allow capturing a vast amount of information, visualization systems help to communicate that information clearly and effectively using graphical representations. This entry first discusses how data sensing technology and visualization systems are used in learning research then discusses the various types of systems and how they are used. It concludes by discussing how the data obtained by ...