• What is the visual quality of an image?
• What is a haptic interface?
• When does a motion platform add training value? When do you not want to use a motion platform?
• What is 3D sound? Is it needed in a simulator? What are its benefits and limitations?
• How long can someone remain in a VE without side effects? How can side effects be prevented in a VE? What are the symptoms of side effects from a VE? How are they measured?
  
  
  
  
  
  
  

What is the visual quality of an image?

The perceived visual quality of an image depends on many characteristics including resolution, color, sharpness, brightness, contract, and accuracy (Lombard & Ditton, 1997). In general, higher resolution images and larger images have both been shown to achieve more feelings of realism in users of simulations (Neuman, 1990, Reeves, Detember, & Steuer, 1993). In addition, images that are more photorealistic, or have characteristics of actual photographs, tend to provoke a greater sense in users then images that are obviously animated (Heeter, 1992). Smaller images, however, may provide equal sensations of realism depending upon the field of view that they occupy. Lombard and Ditton (1997) assert that a large image in a large viewing distance (i.e. IMAX theater) can result in the same sensation of reality as a small image in a small viewing distance (i.e. head mounted display). Overall, images should be as realistic as possible given the confines of the equipment.

See also Visual Resolution
See also Stereoscopy/3D

What is a haptic interface?

             A haptic interface is a device that allows a computer to recreate the sense of touch for users of a virtual reality environment (Brook, 1997). The word "haptic" is derived from the Greek word "haptesthai" meaning "to touch". Haptic interfaces provide force feedback, or a sense of physical resistance, to the fingers of operators of virtual environments. Advanced haptic interfaces simulate the receptors in the fingers, providing users the sensation of actually touching objects in a virtual environment. There are two other important aspects to the sense of touch: kinesthetic information and tactile information. Kinesthetic information conveys the overall properties of an object, such as its position in space. Tactile information conveys the texture of the material being touched, or whether it is moldable, soft, hard, or rough. A well-designed haptic interface will provide both kinesthetic, tactile, and force feedback (Brook, 1997). When the feedback is controlled properly, haptic interfaces greatly increase realism of virtual environments (Heeter, 1992). (Image courtesy of Johns Hopkins University)

See also Force Loading

When does a motion platform add training value? When do you not want to use a motion platform?

             Many simulators and virtual reality devices use motion platforms to create sensations of acceleration, deceleration, and other gravitational forces. Hydraulic motion platforms are often found in sophisticated flight simulators to create a more realistic flight experience for users. Although it is often assumed that the body movement would contribute to a sense of presence, in actuality, little evidence has supported this claim. Instead, moving platforms greatly increase the chance for simulator sickness, which is characterized by symptoms similar to motion sickness including nausea, dizziness, and spatial disorientation. Moving based simulators are more likely to induce nausea then fixed platform simulators (Money, 1991). In addition, the combination of visually induced motion and mechanical motion, especially low frequency vibrations, may cause severe symptoms (Casali & Frank, 1988). This is ironic, because it is generally assumed that adding motion to a virtual environment would increase realism for users. Unfortunately, adding motion to virtual environments has yielded little training benefit to users (McCauley & Sharkey, 1992). If anything, adding motion increases the likelihood of simulator sickness and subsequent performance degradation.

See also Force Loading
See also Simulator Sickness

What is 3D sound? Is it needed in a simulator? What are its benefits and limitations?

             A virtual environment is greatly enhanced by the inclusion of an audio component. Spatialization, or 3D sound, is an attempt to create sound in three dimensions. In such sound systems, the amplitude, phase, and frequency of sounds arriving at each ear are adjusted to create the illusion of dimensional space. For example, 3D sound would simulate to the operator the sound of "footsteps as they echo in a dark, empty corridor" (Lombard & Ditton, 1997). 3D sound is beneficial for simulator users, as it provides yet another sensory input to enhance feelings of presence and realism. Unfortunately, 3D sound also has limitations. Research into 3D sound has shown that there are many aspects of the head and ear shape that affect the recognition of 3D sound. Although there is a mathematical equation to determine proper levels of sound for individuals called a Head Related Transfer Function (HRTF), it is virtually impossible to ensure that each user is experiencing the same sound effects. Therefore, what is beneficial to one user may be distracting to another while operating the simulator (Isdale, 1993). In addition, the software for creating digital sound is still considered largely inadequate (Schneiderman, 1998).

How long can someone remain in a VE without side effects? How can simulator sickness be prevented in a VE? What are the symptoms of side effects from a VE? How are they measured?

            Simulator sickness is a phenomenon similar to motion sickness. However, simulator sickness does not always involve a moving platform, and can occur because of the degree of vection, or simulated motion (Kennedy & Frank, 1985). Symptoms of simulator sickness include nausea, pallor, sweating, headache, and occasional vomiting. Cardiovascular, gastrointestinal, and respiratory changes have also been observed in individuals suffering from simulator sickness (Casali & Frank, 1988). Cybersickness, or discomfort felt after exposure to a virtual environment, is characterized by similar gastrointestinal disturbances in addition to eye and oculomotor problems. 

A widely accepted motion sickness theory is the cue compatibility theory, which asserts that the brain is receiving conflicting cues about the nature of motion (Reason & Brand, 1975). For example, while in the cabin of a ship, an individual is sensing motion through vestibular cues but is viewing a stationary environment through visual cues. When such cues conflict, symptoms of sickness develop. A similar cue conflict phenomenon is thought to occur in simulators and virtual environments, as cues from physical reality are conflicting with cues from virtual reality.

            Simulator sickness and cybersickness is primarily measured using self-report questionnaires. The motion sickness questionnaire (MSQ) has recently been modified to measure both simulator and cybersickness susceptibility (Kennedy, Berbaum, Allgood, Lane, Lilienthal, & Baltzley, 1988). Both questionnaires can be administered before exposure to predict likelihood of symptoms, as well as after exposure to measure any noticeable side effects. Unfortunately, questionnaires are very subjective, and in addition, many side effects of simulator and cybersickness do not always manifest immediately after exposure. It is not uncommon for individuals to develop symptoms days after simulator use (Draper, 1996).

            Side effects can be prevented in two ways. First, users should not stay in a simulator or virtual environment for long periods of time. It is recommended that users begin a "practice round" for no more then 15 minutes, in order to allow adaptation to the virtual environment (Kennedy et al, 1988). Once uses adapt to the environment, exposure times can be increased. In addition, specific design factors can be implemented to minimize sickness symptoms. Kennedy and colleagues (1989) found that flight simulators which cause the most eyestrain tend to have multiple, wide field-of-view cathode ray tubes (CRT) and moving platforms. Minimizing lag time and unnecessary head movements is also crucial to prevention simulator and cybersickness symptoms (Kennedy et al, 1989).

            Minimizing simulator sickness is crucial for training purposes. If individuals begin to develop an apprehension of the simulator due to feelings of sickness, they may be unwilling to use the simulator and learn the necessary skills needed for their job. In addition, if users learn that minimizing their own head movements prevents feelings of sickness, they may be apt to minimize head movements at times when doing so would be extremely dangerous, such as in a real aircraft (Money, 1991).