MILTON P. HUANG, M.D. AND NORMAN E. ALESSI, M.D.
"Presence," as discussed in the virtual reality (VR) literature, is the sense of truly being in a virtual place. This literature explores many aspects of presence including interactive and environmental factors. This exploration has generally ignored the impact of the individual's mental status on the experience of presence. Mental disorders of depression, anxiety, and psychosis may each define a population with specific tendencies to respond to VR in particular ways. To fully understand the experience of presence in virtual environments, we must understand more about the impact of different mental states on presence. Such an understanding will improve our insight into the construct of presence, assist in better design of virtual environments, and better inform us about how virtual environments can be applied in the treatment of emotional disorders.INTRODUCTION
Technology affects how we relate to and understand the world. Technological changes change our perceptions and thinking. The introduction of the printing press created changes in attitudes toward the word of God as embodied in the Bible . The Internet and newer information technologies are changing our concepts of space and privacy . The introduction of Virtual Reality (VR) technologies alters how we think and relate to reality itself. The attempt to improve these technologies and make them more powerful and effective in their impact on people has lead to the exploration of the concept of "presence." In the virtual reality literature, this term refers to the feeling of being in a real place while experiencing a virtual one. Discussion of this concept has lead to different definitions based on behavioral responses, on the ability to differentiate different stimuli, and even on philosophical ideas about how people interact with the environment. These definitions have generally ignored the emotional state of the person experiencing "presence" 3]. Different emotional states have an impact on how individuals react to an environment, and in turn this impact needs assessment if we wish to effectively use virtual environments to teach or change people. This paper will briefly review some of the work that has been done on presence, then explore some of the potential implications mental health has on presence. We will conclude by discussing how these implications affect how we should design and use virtual environments.PRESENCE
Review of the presence literature reveals several different definitions and descriptions of presence. It has often been defined as the "feeling" or "sense" of being present in a virtual environment, indirectly emphasizing the psychological aspects of experience. Nonetheless, there are many variations on this theme. Schloerb  attempts to define presence more objectively as a "probability" about perception. He divides it into "subjective presence" and "objective presence," where subjective presence is the "probability that a person perceives that he or she is physically present in the given environment." Objective presence is the "probability that the specified task is completed successfully." In contrast to such a operational definition, Witmer and Singer  emphasize the subjective aspects, stating presence is "subjective experience of being in one place or environment, even when one is physically situated in another." Heeter  refines subjective experience into three types: "subjective personal presence," "social presence," and "environmental presence." Personal presence is "the extent to which and the reasons why you feel like you are in a virtual world." Social presence is "the extent to which other beings (living or synthetic) also exist in the world and appear to react to you." Environmental presence is "the extent to which the environment itself appears to know that you are there and to react to you." Zahorik and Jenison  move to a completely environmental definition, describing presence as "successfully supported action in the environment." Their definition refers to J. J. Gibson's ecological view of perceptual veridicality, and avoids the need for a subjective sense of presence by suggesting that the effectiveness of the coupling of perceptions and action between the user and the (virtual) environment is presence.
In addition to varying definitions, the presence literature also includes references to important components of presence. Many authors emphasize the importance of "immersion." Slater and Wilbur  define this as an objective measure, describing it as "the extent to which the computer displays are capable of delivering an inclusive, extensive, surrounding, and vivid illusion of reality to the senses of a human participant." In contrast, Witmer and Singer  again emphasize the subjective elements, defining it as a "psychological state characterized by perceiving oneself to be enveloped by, included in, and interacting with an environment that provides a continuous stream of stimuli and experiences." They separate this from "involvement" which they define as a "psychological state experienced as a consequence of focusing one's energy and attention on a coherent set of stimuli or meaningfully related activities and events." Depending on the author and their sense of what creates virtual reality, one finds different emphases placed on different aspects of presence.MENTAL HEALTH AND PRESENCE
An individual's mental condition has a clear effect upon how they experience the world and therefore how they would experience presence in a virtual world. Mental state provides a filter for how people look at the world around them. This filter varies with time and circumstance, and frequently results in dysfunctional behavior. 48 % of people in the US will meet criteria for a clinical psychiatric diagnosis in their lifetime.  Many more may have subclinical syndromes of depression, anxiety, schizophrenia, or simply particular personalities that repetitively affect how they perceive and react to the world around them. These emotional and cognitive predispositions alter perception, learning (both conscious and unconscious), motor responses, engagement with others, and activity in the environment. We will examine a few examples and how they may have affects on the experience of presence.
Depression affects how people perceive their world. It flattens one's feelings and leads to less engagement with the environment. Experiments show that depressed people have faulty judgements about the passage of time.  They are less likely to attend to aspects of their environment such as words with emotional content.  Although they can cognitively identify and label faces with specific emotions, they do not respond emotionally in the same way non-depressed people do. They do not engage in the same level of unconscious mimicry of expression. Such changes in people with depression affect how much they react to an environment. In a virtual environment, it is likely that they would tend not to pay as much attention to the novel or positive aspects of the experience, more easily attending to the flaws and discomforts of the situation. They would think about the bulky headsets or constraining wires instead of becoming involved with the interactive experience that VR equipment can offer. We would speculate that even those with a mild depression or a predisposition to depression from suffering past episodes might also tend to have less engagement with virtual experiences.
Anxiety is a normal feeling everyone should be able to experience. It increases attention and focus when experienced at ideal levels, but creates distraction and dysfunction when levels become more overwhelming. Approximately one in four people in the US will reach a point during their life when anxiety reaches clinically significant levels.  As anxiety increases, an individual may focus too greatly on particular parts of the environment that are perceived as dangerous and ignore other parts. This inhibits learning, even on an unconscious level.  In a virtual environment, we would expect someone with an anxiety disorder or a tendency to anxiety would respond similarly. Virtual elements could trigger fears of embarrassment in social situations, being trapped in closed spaces, etc. These triggers could arise from a stimulus in the virtual environment or from the experience of wearing the equipment itself. Conversely, elements of virtual environments could also improve an anxious person's engagement or performance if fears of being observed in public or other intense anxieties are minimized. The case of anxiety problems suggests we may need to individually tailor virtual environments for each individual depending on their past experiences and what they learned to fear - not necessarily to eliminate the feared situation, but to achieve an optimal level of anxiety for appropriate attention, engagement, and learning.
Schizophrenia and other psychotic disorders affect a person's perceptions and reality testing. Symptoms range from mild ideas of reference about the special meanings of everyday events to frank hallucinations of events that are not real. Although only a little over 1% of the population meets criteria for schizophrenia or schizophreniform disorder, 28% of the population will endorse at least one of the thirteen questions used to probe for psychosis.  The expression of these symptoms varies with the individual. Some interact normally outside the arena of their delusion. Others are more globally impaired. There is a suggestion that such people subjectively experience a loss of focus or their usual sense of self.  This may arise from difficulties in processing context information, information that must be kept in mind to provide proper associations to new stimuli.  Such difficulties in processing information from the environment and properly relating it to the self suggest likely distortions of the sense of presence from what is considered normal. Exposure to a virtual environment may help "normalize" the responses of people with tendency to psychosis if the prominence of the stimuli can overcome the tendency for distraction in processing. On the other hand, the manipulation of presence that occurs in the shift to "virtual presence" may worsen the ability of some to discriminate between real and unreal if their ability to form such judgements was already impaired.CONCLUSIONS
As the above examples suggest, traits of depression, anxiety, or tendency to psychosis will affect an individual's sense of presence. Such traits make people engage differently with the world, sometimes removing themselves, fearfully connecting themselves, or intermittently connecting themselves along different cognitive and emotional dimensions. Everyone experiences presence differently, and presence can serve as a tool for greater understanding of how different minds operate. By understanding the differences in presence that is generated for people with different mental conditions, we can learn more about the how cognitions and emotions are processed. We can also learn more about the potential for how we can best design virtual environments for treating mental disorders.  For example, one traditional treatment for depression is cognitive therapy, targeted at reducing depression by changing a personís tendencies for negative, distorted thoughts.  Virtual environments have the potential of assisting in the identification and challenge of false cognitions, and perhaps even with generally increasing engagement if immersive engagement can be properly directed. Virtual environments are already used in challenging phobias,  and have other potential applications.  Understanding the effect of mental status on presence will expand our skill and vision in understanding how to use virtual environments.
 Morgan NS. Pen, Print, and Pentium. Technological Forcasting and Social Change. (1997); 54: 11-16.
 Huang M P and Alessi N E. The Internet and the Future of Psychiatry. American Journal of Psychiatry. (July 1996); 153: 861-869.
 Huang MP, Alessi NE. Presence as an Emotional Experience. Amsterdam: IOS Press. In Press.
 Schloerb DW. A Quantitative Measure of Telepresence. Presence: Teleoperators and Virtual Environments. (Winter 1995); 4(1): 64-80.
 Witmer BG, Singer MJ. Measuring Presence in Virtual Environments: A Presence Questionnaire. Presence:Teleoperators and Virtual Environments. (June 1998); 7(3): 225-240.
 Heeter C. Being There: The Subjective Experience of Presence. Presence: Teleoperators and Virtual Environments. (Spring 1992); 1(2): 262-71.
 Zahorik P, Jenison RL. Presence as Being-in-the-World. Presence: Teleoperators and Virtual Environments. (February 1998); 7(1): 78-89.
 Gibson JJ. The ecological approach to visual perception. Boston: Houghton Mifflin, 1979.
 Slater M, Wilbur S. A Framework for Immersive Virtual Environments (FIVE): Speculations on the Role of Presence in Virtual Environments. Presence:Teleoperators and Virtual Environments. (December 1997); 6(6): 603-616.
 KesslerRC, McGonagle KA, Zhao S, Nelson CB, Hughes M, Eshleman S, Wittchen H-U, Kendler KS. Lifetime and 12-month prevalence of DSM-III-R psychiatric disorder in the United States: Results from the National Comorbidity Survey. Archives of General Psychiatry. (January 1994); 51(1):8-19.
 Blewett AE. Abnormal Subjective Time Experience in Depression. British Journal of Psychiatry. (1992); 161:195-200.
 Wexler BE, Levenson L, Warrenburg, Price LH. Decreased Perceptual Sensitivity to Emotion-Evoking Stimuli in Depression. Psychiatry Research. 51:127-138.
 Rathus JH, Reber AS, Manza L, Kushner M. Implicit and Explicit Learning: Differential Effects of Affective States. Perceptual and Motor Skills. (1994); 79:163-184.
Kendler KS, Gallagher TJ, Abelson JM, Kessler RC. Lifetime Prevalence, Demographic Risk Factors, and Diagnostic Validity of Nonaffective Psychosis as Assessed in a US Community Sample: The National Comorbidity Survey. Archives of General Psychiatry. (November 1996); 53(11): 1022-1031.
Yoshiharu K, Takemoto K, Mayahara K, Sumida K, Shiba S. An Analysis of the Subjective Experience of Schizophrenia. Comprehensive Psychiatry. (November/December 1994); 35(6): 430-436.
Servan-Schreiber D, Cohen JD, Steingard S. Schizophrenic Deficits in the Processing of Context: A Test of a Theoretical Model. Archives of General Psychiatry. (December 1996); 53(12): 1105-1112.
Huang MP, Himle J, Beier K, Alessi NE. Challenges of Recreating Reality In Virtual Environments. Cyberpsychology and Behavior. (1998)Vol 1 (2):163-168.
Beck AT, Shaw BF, Emery G, Rush AJ. Cognitive Therapy of Depression. New York: Guilford Press, 1989.
 MP Huang, J Himle, K Beier, NE Alessi. Comparing Virtual and Real Worlds for Acrophobia Treatment. In: JD Westwood, HM Hoffman, D Stredney, and SJ Weghorst, (eds.) Medicine Meets Virtual Reality: Art Science, Technology: Healthcare (R)evolution. IOS Press, Amsterdam, 1998.
Glantz K, Durlach NI, Aviles WA: Virtual Reality (VR) and Psychotherapy: Opportunities and Challenges. Presence: Teleoperators and Virtual Environments. Vol 6 (1), pp. 87-105, February 1997.
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