presence

Three Ways to Measure Presence in VR

bike sunset.jpeg

In writing my post about how taking physical action increases presence in VR, I got curious - how is presence being measured?  That turned out to be such a big question that it needed a separate post.  Here’s a round up of definitions and ways to measure presence.  I’ve tried to organize the info in a way that helps people who are actively doing user experience research in VR.  

In short, presence is the notion of “being there,” inside of a digital experience.  Here’s a longer definition: 

1. High resolution information displayed to the participant, in a manner that does not indicate the existence of the display devices. 

2. Consistency of the displayed environment across all sensory modalities;

3. The possibility of the individual being able to navigate through and interact with objects in the environment, including interaction with other actors which may spontaneously react to the individual;

4. The individual’s virtual body, their self-representation within the environment, should be similar in appearance or functionality to the individual’s own body, and respond appropriately to the movements of their head, eyes, and limbs;

5. The connection between individual’s actions and effects of those actions should be simple enough for the individual to quickly learn.

Each of these is naturally maximized in the context of a person acting in everyday life (Usoh, Catena, Arman, and Slater 2000).

The concepts of presence, immersion, and performance have been studied in VR for more than 20 years so there are many different sources to draw on. I’m going to discuss how physical, psychological, and behavioral data on presence is collected. 

Physical Evidence of Presence

Physical signs that can be objectively measured (rather than reported by the participant) are attractive to researchers. Heart rate is one such metric. A lesser know measure is the Galvanic skin response (GSR). When a human experiences psychological arousal, a broad term meaning they are alert, awake, and attentive, then their skin becomes temporarily better at conducting electricity. The implication for VR is that if people are going through an experience and their skin conductance increases, then you would assume that participants have a stronger sense of “being there” inside of an experience.  More details on GSR from the MIT Media Lab:

The skin conductance response is measured from the eccrine glands, which cover most of the body and are especially dense in the palms and soles of the feet. (These are different from the apocrine sweat glands found primarily in the armpits and genital areas.) The primary function of eccrine glands is thermoregulation -- evaporative cooling of the body -- which tends to increase in aerobic activity, so yes, activity can affect conductance. However, the eccrine glands located on the palms and soles have been found to be highly sensitive to emotional and other significant stimuli, with a measurable response that precedes the appearance of sweat…Arousal has been found to be a strong predictor of attention and memory.

In the case of the heart rate or the GSR, they are useful for signaling to designers that something is happening inside of the experience. However, more steps are necessary to determine exactly what is the user’s experience. Measuring heart rate or arousal is different from measuring what people are feeling. To learn that, you will have to ask participants or analyze their behavior.  

Assessing Psychological Presence

There are loads of existing survey questions that you could co-opt for your own user research.  The Slater, Usoh and Stead (1995) and Witmer and Singer (1998) questionnaires are both very highly cited.  Consider what the aims of your study are when deciding what type of survey questions to use with your participants.  

Click  here  to download a commercial from the MIT Media Lab on their skin conductance measurement device, the Galvactivator

Click here to download a commercial from the MIT Media Lab on their skin conductance measurement device, the Galvactivator

Witmer and Singer (1998) has 32-questions and covers the domains of Control, Sensory Input, Distraction, and Realism.  Example questions:

A. How much were you able to control events? 

B. How compelling was your sense of objects moving through space? 

C. How aware were you of your display and control devices? 

Questions from Slater, Usoh, and Stead (1995) are below: 

1. Please rate your sense of being in the virtual environment, on a scale of 1 to 7, where 7 represents your normal experience of being in a place. 

2. To what extent were there times during the experience when the virtual environment was the reality for you? 

3. When you think back to the experience, do you think of the virtual environment more as images that you saw or more as somewhere that you visited? 

4. During the time of the experience, which was the strongest on the whole, your sense of being in the virtual environment or of being elsewhere? 

5. Consider your memory of being in the virtual environment. How similar in terms of the structure of the memory is this to the structure of the memory of other places you have been today? By ‘structure of the memory’ consider things like the extent to which you have a visual memory of the virtual environment, whether that memory is in color, the extent to which the memory seems vivid or realistic, its size, location in your imagination, the extent to which it is panoramic in your imagination, and other such structural elements. 

6. During the time of your experience, did you often think to yourself that you were actually in the virtual environment? 

Behavioral analysis

When conducting user research, it's ideal to film the participant so you have the opportunity to view the footage afterward.  You might not know exactly what behavior you are looking for until you’re already on the last participant of the day.  It most cases it will work to take an inductive approach and learn what behaviors are important by observing people going through your experience.  

Examples of behaviors to track would be how people are interacting with menus.  Do they have to make multiple attempts to accomplish a task? Are they taking time to read your instructions or do they just dive right in?

Key Takeaways

  • Don't try to reinvent the wheel when it comes to measuring presence - there's plenty of valid and reliable research to draw on.  
  • Combine various sources of data in order to build the most robust results.
  • Physical data typically only tells you that something is happening (increased heart rate or skin conductance), but not what the user's actual experience is.  
  • Surveys are used to gather psychological measures.  An advantage of them is that data collected can easily be compared over time and across experiences / platforms / etc.
  • Behavioral data can be tricky to collect because you may not know what you’re looking for, but it’s essential to telling the complete story of the user experience. 

 

Further reading

Galvactivator FAQ product page at the MIT Media Lab. 

Slater, M., Usoh, M., & Steed, A. (1995). Taking steps: the influence of a walking technique on presence in virtual reality. ACM Transactions on Computer-Human Interaction (TOCHI), 2(3), 201-219.

Slater, M., McCarthy, J., & Maringelli, F. (1998). The influence of body movement on subjective presence in virtual environments. Human Factors: The Journal of the Human Factors and Ergonomics Society, 40(3), 469-477.

Usoh, M., Catena, E., Arman, S., & Slater, M. (2000). Using presence questionnaires in reality. Presence: Teleoperators and Virtual Environments, 9(5), 497-503.

 

Reality Is What You Do (Not What You See)

“Being there” means the capability to act there. 

“Being there” means the capability to act there. 

Your perception of reality is based on what you can do.  When you are inside of a VR environment, the more functionality that you have, the more the experience resembles your every day life.  You believe an object is real when you can interact with it, not just when you see it.  

Presence is defined as a sense of “being there,” or the extent to which virtual environments are perceived as places visited rather than images seen.  If you accept that presence is a design ideal for VR environments, there are systematic ways to increase users’ feelings of it.  Here I review two scientific papers on using body movement to heighten presence.  

Locomotion: Walking in Place vs. Using a Mouse

The degree of presence depends on the match between proprioceptive and sensory data.  Researchers at the University of London asked people to walk in place while they were inside of a virtual experience.  The gaze of the participant in the HMD determined what direction people felt they were walking in.  They compared the walking-in-place experience against the use of a computer mouse for locomotion.  The researchers believed that walking in place offered an advantage because is that it doesn’t require people to use their hands for navigation.  

The hand may be entirely reserved for the purposes for which it is used in everyday reality, that is, the manipulation of objects and activation of controls.
— Slater, Usoh & Steed (1995)
Valve's The Lab uses a teleportation function built into the hand controllers.  The user points a light beam where they want to go and release the trigger to teleport.  In this case, the user will land in the green circle in front of them.

Valve's The Lab uses a teleportation function built into the hand controllers.  The user points a light beam where they want to go and release the trigger to teleport.  In this case, the user will land in the green circle in front of them.

From the Slater, Usoh, M. and Steed, A. (1995) article: 

A fundamental requirement for an effective virtual reality is, therefore, that there is a consistency between proprioceptive information and sensory feedback, and in particular, between the mental body model and the virtual body…Proprioception is “the continuous, but unconscious sensory flow from the movable parts of our body (muscles, tendons,joints) by which their position and tone and motion [are] continually monitored and  and adjusted, but in a way that ishidden from us because it is automatic and unconscious.” (Sacks 1985).  Proprioception allows us to form a mental model that describes the dynamic spatial and relational disposition of our body and its parts. We know where our left foot is (without having to look) by tapping into this body model. We can clap our two hands together (with closed eyes) similarly by relying on this unconscious mental model formed from the proprioceptive data flow.

The control groups (the “pointers”) navigated the environment using a 3D mouse, initiating movement by pressing a button, with direction of movement controlled by pointing. The experimental groups (the “walkers”) used the walking technique. In each case the mouse was also used for grasping objects. The task was to pick up an object, take it into a room, and place it on a particular chair. The chair was placed in such a way that the subjects had to cross a chasm over another room about 20 feet below in order to reach it…With respect to the ease of navigating the environment, subjects in both experiments marginally preferred to use the pointing technique. This result was not surprising: as Brooks et al. [ 1992] noted, with the real treadmill more energy certainly is required to use the whole body in a walking activity, compared to pressing a mouse button or making a hand gesture (or driving a car, with respect to the similar comparison in everyday reality).

This is quite interesting…People found that the mouse was EASIER, but walking was more natural.  More evidence that the best experiences might not be the easiest ones.

Other results showed that “for the “walkers” the greater their association with the virtual body the higher the presence score, whereas for the “pointers” there was no correlation between virtual body association and the presence score. In other words, participants who identified strongly with the virtual body had a greater degree of reported presence if they were in the “walking” group than if they were in the “pointing” group. Association with the virtual body is important.…We argue that the walking technique [helps people match their proprioception to their sensory information,] compared to the pointing technique,and therefore other things being equal should result in a greater sense of presence. However, we found that this is modified by the degree of association of the individual with the virtual body…The virtual body association is significantly positively correlated with a subjective presence for the walkers but not for the pointers, which is certainly consistent with the proposed model.

This is important because it means that Samsung Gear VR experiences where a person is represented as a black hole and has no virtual body, presence is going to be very difficult to create.

Beyond Walking: The Influence of Bending, Standing, and Task Complexity on Presence

The researchers of the walkers vs. pointers study conducted a follow up experiment where they asked people to “walk” in place through a forest.  They varied the height of the trees for some participants, meaning that when there was high (vs. low) variability, people inside of the experiment had to bend down and look up more.  

The results showed a significant positive association between reported presence and the amount of body movement, in particular head yaw, and the extent to which subjects bent down and stood up…The practical importance of the results of this experiment is that since there does seem to be a relationship between body movement and presence, it is a reasonable goal to design interactive paradigms that are based on semantically appropriate whole body gestures. These will not only seem more ‘natural’, but may also increase presence. We further believe that the increase in presence in itself will engender more body movement, which in turn will generate higher presence, and so on.

Interestingly, adding a layer of cognitive effort did not increase user feelings presence.  They manipulated task complexity by asking some participants to count the number of trees that they saw and remember the distribution of diseased trees.  However, there was no increase in presence by having to exert mental effort.  

Head Yaw is Good for Presence

Head Yaw is Good for Presence

Using Walking in Place to Make Stairs and Ladders

If you are doing a Harry Potter wizarding experience, then flying or teleporting might be the best locomotion.  However, if you are trying to do an education simulation, such as training fire fighters, consider integrating more humdrum actions.  

The same idea [of walking-in-place] can be applied to the problem of navigating steps and ladders. One alternative is to use the familiar pointing technique and to “fly.” While in some applications there maybe a place for such magical activity, the very fact that mundane objects such as steps and ladders are in the environment would indicate that a more-mundane method of locomotion be employed. The walking-in-place technique carries over in a straightforward manner to this problem. 

When the collision detection process in the virtual reality system detects a collision with the bottom step of a staircase, continued walking will move the participant up the steps. Walking down the steps is achieved by turning around and continuing to walk. If at any moment the participant’s virtual legs move off the steps (should this be possible in the application), then they would “fall” to the ground immediately below. Since walking backward down steps is something usually avoided, we do not provide any special means for doing this. However, it would be easy to support backward walking and walking backward down steps by taking into account the position of the hand in relation to body line: a hand behind the body would result in backward walking.

Ladders are slightly different; once the person has ascended part of the ladder, they might decide to descend at any moment. In the case of steps, the participant would naturally turn around to descend. Obviously this does not make sense for ladders. Also, when climbing ladders it is usual for the hands to be used. Therefore, in order to indicate ascent or descent of the ladder, hand position is taken into account. While carrying out the walking-in-place behavior on a ladder, if the hand is above the head then the participant will ascend the ladder and descend when below the head. Once again it is a whole-body gesture, rather than simply the use of the hand, that is required in order to achieve the required result in an intuitive manner. If at any time the virtual legs come off the rungs of the ladder, then the climber will “fall” to the ground below.

Key Takeaways to Maximize Presence in VR

  • Presence is defined as the user’s sense of “being there” inside of a simulated environment.  
  • The way that you believe you can interact with your environment is just as important as what you see in VR.
  • Walking-in-place has been proven to be a metaphor for locomotion and navigation that increases presence.
  • There is evidence that using body movements such as walking, bending down, and moving your head also heightens a sense of presence.
  • Cognitive complexity does not increase a sense of presence.  

Further reading

Sacks, Oliver. (1985). The Man Who Mistook His Wife for a Hat. Picador, London.

Slater, M., McCarthy, J., & Maringelli, F. (1998). The influence of body movement on subjective presence in virtual environments. Human Factors: The Journal of the Human Factors and Ergonomics Society, 40(3), 469-477.

Slater, M., Usoh, M., & Steed, A. (1995). Taking steps: the influence of a walking technique on presence in virtual reality. ACM Transactions on Computer-Human Interaction (TOCHI), 2(3), 201-219.