Behavioral and Physiological Methods

Virtual reality (VR) systems enable the user to feel as if they are present in a computer generated environment. But how do we determine the extent to which a user feels present in the virtual environment? This chapter examines three categories of methods commonly used for measuring presence; their use in the field, advantages, and disadvantages. Subjective measures rely on self-assessment by the user. Users answer questions such as "How real did the environment seem to you?", "Was the environment like a place you visited, or a series of images presented to you?". Behavioral measures examine actions or manners exhibited by the user that are responses to objects or events in the virtual environment. For example, does the user duck if a virtual object is thrown at his head. Physiological methods attempt to measure presence by gauging changes in the subject's heart rate, skin temperature, skin conductance, breathing rate, etc. In a stress-inducing virtual environment does the user exhibit physiological signs of stress? How do these methods compare when using the criteria of reliability, validity, objectivity, and sensitivity.