Mariano Alcan ˜ iz* Instituto en Bioingenieria y Tecnologia Orientada al Ser Humano Universidad Polite ´cnica de Valencia Institute for Research and Innovation in Bioengineering Camino Vera s/n 46022 Valencia, Spain Beatriz Rey Instituto en Bioingenieria y Tecnologia Orientada al Ser Humano Universidad Polite ´cnica de Valencia Jose Tembl Vera Parkhutik Neurology Service Hospital Universitari La Fe Presence, Vol. 18, No. 2, April 2009, 97–111 © 2009 by the Massachusetts Institute of Technology A Neuroscience Approach to Virtual Reality Experience Using Transcranial Doppler Monitoring Abstract Virtual reality enables people to behave and feel as if they were present in a virtual environment and therefore is a useful tool in many fields. In order to study the use- fulness of virtual environments, the concept of presence is examined. Up to now, the most common method to measure presence has been to use subjective mea- sures based on validated questionnaires about user experience. However, more objective measurements, such as physiological measurements, are now being con- sidered. In this study, transcranial Doppler (TCD) sonography is presented as a brain activity measurement technique that can be used to study presence in virtual environments. Thirty-two subjects navigated in a virtual environment in different immersive conditions while TCD was monitored. The results show that there are changes in blood flow velocity in the subjects during moments associated with dif- ferent levels of presence. 1 Introduction Immersive virtual environments (VEs) allow users to have unique experi- ences that were never possible before, and although users know from a cogni- tive point of view that the VE is not a real place, they act and think as if the VE were real. VEs take advantage of people’s imaginative ability to psychologi- cally transport their presence to another place. Since VEs are being used successfully in many fields (Stone, 2002), it is nec- essary to have a reliable measure of their usefulness. One possible measure (in- dependent of the application) that has been proposed (Held & Durlach, 1992; Sheridan, 1992; Stanney, Mollaghesemi, Reeves, Breaux, & Graeber, 2003) is the concept of presence. Although there is still a lack of concise definitions of the construct of presence, a commonly accepted definition is that presence is the subjective experience of being in one place, even when physically located in another (Ban ˜os et al., 2005; Sadowski & Stanney, 2002; Slater & Wilbur, 1997; Sheridan, 1992). Presence is the process of discerning and validating the existence of self in the natural world, a process humans have engaged in since birth. A sense of presence in a VE derives from feeling as if you exist within, but as a separate entity from, a virtual world that also exists (Heeter, 1992). Other definitions *Correspondence to malcaniz@labhuman.upv.es. Alcan ˜iz et al. 97