Abstract:
A system and method of generating an immersive digital image sequence capable of providing a perception of self-motion, includes the steps of: generating the digital image sequence; and adjusting the digital image sequence to control the perception of self-motion, whereby the degree of motion sickness induced in a viewer of the digital image sequence is controlled.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to the processing and display of digital image sequences and, more particularly, to ameliorating motion sickness induced in viewers of the image sequences.  
         BACKGROUND OF THE INVENTION  
         [0002]    In a visual display system that depicts a real world motion scene, many people may experience motion sickness, or more precisely, simulator sickness. Individuals experiencing slight levels of simulator sickness may experience some level of positive effects, such as excitement. However, beyond some threshold, the viewer may begin to experience a number of negative effects such as light-headedness, nausea, headache and other undesirable symptoms. It is well understood that providing conflicting or inconsistent psychological cues to a viewer induces this particular type of illness.  
           [0003]    In the type of system relevant to the present invention, the display system may provide visual stimulation that provides the perception that a viewer is undergoing motion. However, the individual&#39;s vestibular and/or proprioceptive system may not provide similar stimulation. Instead these systems may indicate the viewer is stationary (or when watching imagery while in a moving vehicle, not consistent with the visual or vestibular system). When conflicting cues are provided to a viewer, the viewer may experience a particular class of simulator sickness. Different people have different susceptibility to this type of sickness and the probability that any individual will experience sickness is dependent upon their susceptibility to this type of sickness and the strength of the visual stimulus.  
           [0004]    Individual sensitivity to motion sickness varies quite dramatically. Among the known variables which effect sensitivity to motion sickness are:  
           [0005]    Age:younger individuals are generally more susceptible than older individuals  
           [0006]    Sex:females are generally more susceptible than males  
           [0007]    Race:individuals of Asian background are more susceptible than Europeans or Africans  
           [0008]    Expectations and Previous Experience:individuals who have experienced simulator sickness are more likely to experience it in the future.  
           [0009]    The strength of the visual stimulus for producing motion sickness is influenced by a number of factors. First, vection (the visually induced perception of self-motion) almost never occurs for display systems that span only a small proportion of the users&#39; visual field of view. However, vection is typically thought to be a necessary pre-cursor to this type of sickness. Therefore, the visual stimulus that induces simulator sickness will be stronger for images that are displayed to fill a large proportion of the users&#39; visual field. Further the strength of the percept will be highly dependent on the region of the image that is undergoing motion. Second, the amount of optical flow (or edges representing motion) will influence the onset of this class of simulator sickness. Images with few edges or little detail are less likely to produce this class of simulator sickness than images with significant texture and numbers of edges. Third, since the vestibular system is most sensitive to changes in acceleration, images which depict changing acceleration are more likely to produce sickness than images depicting a constant velocity. Fourth, if an image sequence is captured in stereo with faithful stereoscopic cues, the system may elucidate stronger vection and be more likely to induce illness. Fifth, the depiction of other conflicting information is also likely to increase the probability of the onset of motion sickness. For example, if the image sequence information portrays the viewer navigating the world in a fixed-wing aircraft, then a portion of the image sequence indicating that the viewer is moving backwards is inconsistent with the users&#39; frame of reference. Likewise, an automobile that rolls more than 45 degrees without rolling over may also be considered as providing information that is inconsistent with the users&#39;frame of reference. In either of these situations and others that provide conflicting information, the viewer is more likely to experience illness.  
           [0010]    There is a need therefore for an improved method of generating a digital image sequence that reduces the degree and incidence of motion sickness in viewers.  
         SUMMARY OF THE INVENTION  
         [0011]    A method of generating an immersive digital image sequence capable of providing a perception of self-motion, includes the steps of generating the digital image sequence and adjusting the digital image sequence to control the perception of self-motion, such that the degree of motion sickness induced in a viewer of the digital image sequence is controlled.  
         ADVANTAGES  
         [0012]    The present invention has the advantage that it reduces the degree and incidence of motion sickness in viewers of digital image sequences. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a block diagram of an imaging system useful for practicing the present invention;  
         [0014]    [0014]FIG. 2 is a detailed flow diagram illustrating the viewer interaction process used in one embodiment of the present invention;  
         [0015]    [0015]FIG. 3 is an illustration of a viewer interface message used with the present invention;  
         [0016]    [0016]FIG. 4 is another illustration of a viewer interface message used with the present invention;  
         [0017]    [0017]FIG. 5 is a block diagram illustrating an alternative embodiment of the present invention;  
         [0018]    [0018]FIG. 6 is a flow diagram illustrating a method for image analysis used in the present invention;  
         [0019]    [0019]FIG. 7 is a detailed flow diagram illustrating the editor interaction process used in a third embodiment of the present invention,  
         [0020]    [0020]FIG. 8 is a block diagram illustrating a third embodiment of the present invention;  
         [0021]    [0021]FIG. 9 is viewer a flow diagram of the steps of using the system of FIG. 8; and  
         [0022]    [0022]FIG. 10 is an illustration of a viewer interface screen that allows the viewer to modify the characteristics of the target display system. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    The present invention provides a method and system for altering a digital image sequence that has been captured, pre-rendered, or that is being rendered in real-time in order to reduce the occurrence of motion sickness. This method and system may also utilize knowledge of the display and an analysis of the digital image sequence to determine the propensity of the displayed digital image sequence to produce motion sickness. This analysis is used to determine the portions of the digital video sequence to be altered. The present invention also considers viewer characteristics in order to determine when and to what degree the digital image sequence should be altered.  
         [0024]    One embodiment of a system useful for practicing the present invention is shown in FIG. 1. Referring to FIG. 1, the system contains a digital image sequence storage device  10 , a digital image processor  12 , a digital image sequence display system  14 , and a viewer input device  16 . The digital image sequence storage device  10  may be any electro-optical or -magnetic storage device, such as a hard drive, compact disk (CD) reader, digital video disk (DVD) reader, or network connection capable of delivering digital image sequence information. The digital image sequence storage device  10  contains multiple versions of a digital image sequence with different degrees of motion stimulation.  
         [0025]    The processor  12  may be any general or specialized processor capable of supporting viewer interaction, selection of digital image sequence clips, and display of selected video sequence clips. The display  14  may be any digital image sequence display, including direct view and projection displays. The display  14  may be based on any known electronic display technology, including Organic Light Emitting Diode, Digital Micro-Mirror, Liquid Crystal, Cathode Ray Tube, or Ferro-Electric technology. However, the system preferably employs an immersive display system (i.e., a system that provides a large field of view to the user) such as might be applied in digital cinema or virtual reality systems which presents imagery to either a single person or a group of individuals. The viewer input device  16  that is used may be any input device including a keypad, keyboard, mouse, slider bar, data glove, joystick or any other device that allows the viewer to select among a few discrete options.  
         [0026]    [0026]FIG. 2 shows a flow chart of the operation of the system according to the present invention. Referring to FIG. 2, using information about the display system, the system receives  18  the display characteristics and determines  20  whether any users are likely to experience simulator sickness. If motion sickness is unlikely, the highest vection path through the image sequence is selected  22 . The image sequence is then displayed  24  to the viewer(s). If the field of the view of the display is large enough to provoke motion sickness, the viewer is provided  26  the ability to select the amount of stimulation he or she desires using an interactive display screen and input device. This interactive screen may provide options similar to those shown in FIG. 3. Referring to FIG. 3, a screen  28  displays instructional text  30  and a list of potential selections  32 . Once the viewer makes a selection  34  a particular path in a multiple path image sequence is selected  36  utilizing knowledge of the display system such that the path provides the viewer with an amount of motion stimulation commensurate with his or her selection. The sequence is then composed from the chosen clips and displayed  24 . As long as the viewer does not initiate an action with his or her input device, the sequence continues to play.  
         [0027]    The sequence may reach the end with no viewer input. However, if during the sequence the viewer begins to experience any degree of discomfort or boredom, he or she may use  38  the input device to display  46  another interactive screen  40  such as the one shown in FIG. 4 and to reduce or increase the amount of self motion stimulation. Referring to FIG. 4, the screen  40  displays instructional text  42  and a list of potential selections  44 . Once another selection is made, the system obtains  48  this preference and a new path in the multi-path sequence is selected  50  to provide the appropriate level of motion stimulation. The new path through the sequence is then composed and the display  24  of the sequence is resumed with the newly selected path.  
         [0028]    Referring to FIG. 5, in an alternative embodiment of the present invention the system additionally includes one or more sensors  52  for sensing, recording, and analyzing a human physiological response and a source  54  containing a viewer profile and history data.  
         [0029]    The source  54  for viewer profile or history data may be any networked computer database or a portable data device, such as a magnetic card, that may be transported with the viewer.  
         [0030]    The physiological-response measuring device  52  may be any device capable of sensing increases in sympathetic nervous system activity and/or decreases in parasympathetic nervous system activity. Such devices  52  may include instruments capable of measuring the pallor (de-saturation due to loss of blood flow) of extremities (particularly hands and face), heart rate variability, galvanic skin response, eye movements, drowsiness (eyes closed), breathing rate and volume, temperature of extremities and regularity of gastrointestinal muscle activity.  
         [0031]    Referring to FIG. 6, a high-level flow chart of the actions performed by the system of FIG. 5 is shown. First information about the display device to be used is retrieved  56 . A viewer swipes a magnetic card through a reader before entering the display system. This identifies the viewer and recalls historical information from an on-line database. The system then evaluates the viewer&#39;s history to determine  58  the viewer&#39;s propensity towards motion sickness. This historical information may include information regarding the users&#39; gender, race, or medical information that may provide some information on how likely the viewer is to experience sickness. The historical data may also contain information on previous experiences including the peak value in the simulator sickness propensity measure calculated in the previous step for all previously viewed experiences, and a list of these experiences where the viewer indicated some sensation of simulator sickness.  
         [0032]    Based on this historical data, an aim peak value will be set  60  for the simulator sickness propensity measure. If the viewer has indicated the sensation of simulator sickness in recent experiences, this value will be set to a value smaller than the peak value obtained during that experience. If however, the viewer has not experienced this sensation recently and there is a long-term history demonstrating a peak value above which the viewer often experiences sickness then the system will adopt this peak value. If the viewer has not indicated sickness recently and there is no long-term history available, then the aim peak value will be set to a value higher than the average peak value obtained during their three most recent experiences.  
         [0033]    The system then obtains information  104  regarding the propensity of the digital image sequence stream to induce simulator sickness. This propensity must be understood for individual digital image sequence clips within the digital image sequence stream or as a time series signal that accompanies the digital image sequence information. This signal may accompany the digital image sequence information and be stored with the digital image sequence, a storage device, or the digital image sequence information may be processed to determine this signal.  
         [0034]    [0034]FIG. 7 shows a method that may be used to calculate a time-varying measure that will correlate to the likelihood that the digital image sequence information will induce simulator sickness. Referring to FIG. 7, sequences of image frames that were recorded in a time sequence are analyzed  64  to determine motion vectors between each pair of frames. The actual method used to compute the motion can vary. For example, high-speed block-based motion methods or optical-flow-based algorithms can provide dense motion vectors. Alternatively, feature-tracking methods may be used to provide a sparse yet accurate set of motion vectors through a sequence of images. These motion vectors are then analyzed to determine if they are consistent with camera movement within a 3D space.  
         [0035]    The estimation of camera motion from image sequences is known as ego-motion estimation and there are several well-known algorithms for estimating this. A test  66  is performed to determine if ego motion is present. If the motion vectors between any two frames are not consistent with camera movement then the time lapse between these two images is classified as being non-provocative and the instantaneous value is set to 0  68 . If the motion vectors between the two frames are consistent with camera movement through a 3D space, the motion vectors are further analyzed to determine  70  the speed and direction of motion, and determine camera acceleration  72 . The speed and direction of motion may then be further analyzed (not shown) to determine if the direction of motion is consistent with the environment in which the viewer is being depicted.  
         [0036]    An instantaneous indication of the propensity of the digital image sequence to provoke simulator sickness may then be calculated based upon the information determined from analyzing the sequence of digital image sequence frames. To perform the calculation, the final resolution and field of view for the display is used to transform  74  the edge motion vectors to visually relevant units, such as degrees of visual arc per second. The most likely point of gaze of the user is then determined  76  by finding the most stable point in the image. The edge motion vector lengths are then summed  78  within each of a number of spatial zones at different distances from the center of the image. A weighted average is then computed  80  from these sums such that an edge undergoing motion far from the center of the display is likely to have a larger impact than this same edge when it is presented in the center of the display. A weighting may then be applied  82  to this value by multiplying by a value of 1 plus a constant, times absolute value of the acceleration in visually relevant units, such as degrees of visual arc per square second. A determination  84  is made as to whether stereo information is being displayed. If stereo information is being displayed, a weighting constant greater than 1 is set  86 . If stereo is not being displayed, the weighting factor is set  88  to 1. The value can then be multiplied 90 by the weighting constant. A test is performed  92  to determine if the velocity and acceleration of the imagery is consistent with the depicted environment. If not, an environment weight is set  94  to a value greater than 1. If so, then the environment weight is set  96  to 1. The value is then multiplied  98  by the environment weight.  
         [0037]    Because the onset of motion sickness is not instantaneous but builds up over time, a time constant is set  100  and a time-weighted average of the values is computed  102 . In the alternative embodiment in which the image sequence is generated rather than stored and re-played, the same characteristics as those described can be analyzed to measure the sequence&#39;s predilection to induce motion sickness. Preferably, the information relevant to the desired level of motion sickness inducing imagery can be used to create an appropriate sequence in the first place. In this embodiment, no analysis of the sequence specification is necessary. Rather, the sequence is constructed with specific constraints reducing the likelihood of inducing motion sickness in a viewer. If modification of the sequence is necessary in response to viewer action, the appropriate modified constraints can be applied in real-time to create an alternative sequence with reduced predilection to induce motion sickness.  
         [0038]    Referring again to FIG. 6, once the propensity measure is calculated  104  for the image sequence or specification, this time varying value is then compared to the aim peak value to determine  106  if the digital image sequence will provide a propensity value that is higher than the peak value for the individual. If the digital image sequence does provide a sickness propensity value higher than the aim peak value, the imagery is processed to reduce the peak value of the digital image sequence. The digital image sequence stream or specification may be processed in any number of ways to reduce this value. Among the approaches that might be applied are:  
         [0039]    alter the velocity of motion and acceleration in the digital imagery by interpolating frames in the digital image sequence, effectively reducing the perceived velocity and acceleration within the digital image sequence;  
         [0040]    apply spatial filtering or contrast reduction to the imagery to reduce the number and the contrast of edges in the digital image sequence, especially near the edges of the display or away from the main subject matter that would normally be presented at the edge of the display;  
         [0041]    presenting a uniform area in the peripheral portions of the digital video signal, effectively reducing the field of view of the display system,  
         [0042]    select a digital image sequence clip with similar content but less provocative motion;  
         [0043]    skip particularly provocative portions of the digital image sequence;  
         [0044]    remove the stereo information from the scenery, if the digital image sequence is available in stereo, copying the information that would be presented in one stereo channel to both stereo channels;  
         [0045]    add conflicting or distracting information to the image, such as image noise, which may detract from the perception of vection or reduce the perceived speed of motion;  
         [0046]    add a fixed frame of reference to the imagery, such as a stable horizon line or aircraft airframe on which the viewer can fixate to reduce the perception of self motion;  
         [0047]    if the imagery is generated, the maximum camera velocity and acceleration may be limited;  
         [0048]    if the imagery is generated in an interactive system, the ratio between viewer input to a viewer input device and changes to the system behavior will be reduced (e.g., the ratio of the displacement of a steering wheel to radius of turn will be reduced or the ratio of the displacement of an accelerator to the change in velocity may be decreased).  
         [0049]    Depending upon the amount of reduction required in the sickness propensity value, any one or a combination of these techniques may be selected  108  and applied  110  to reduce the stimulus for motion sickness in the scene.  
         [0050]    It may be observed by one skilled in the art that many of the spatial image manipulations discussed above may require a substantial number of processing cycles to complete in real time. A particularly attractive embodiment of this invention therefore, performs the spatial filtering operation(s) noted above by decreasing the image fidelity of a JPEG, JPEG 2000, or MPEG compressed image. This manipulation is performed by disregarding certain high-frequency bands that could be decompressed and displayed within these or any other hierarchical image compression format. This operation may be performed in a spatially uniform or spatially non-uniform fashion.  
         [0051]    A base-line reading of viewer physiology is then captured  112  by measuring human physiology such as the participants&#39; galvanic skin response and the color of the skin on the back of the hand or the forehead. When the digital image sequence information is available, it is then displayed  114  to the viewer. As the digital image sequence is displayed  114 , the galvanic skin response and pallor of the viewer is measured  116  before and during each scene that is indicated as being provocative based on the analysis of the motion vectors. Additionally, the viewer input device is monitored  118  to determine if the viewer is signaling a desire to change the amount of motion stimulus. If a significant change in physiology (e.g., GSR and/or pallor) is measured  120  during a motion clip or if the viewer signals  122  a desire to change the amount of motion stimulus, the system determines  124  if a flag to indicate that onset of sickness has already been set. If not, the flag is set  126 , a more aggressive means of altering the image sequence is chosen  128  and the image sequence is altered  130  further before displaying  114  it to the viewer. If the flag is already set, the system determines  132  if the physiology is improving. If it is, then the current method of filtering is improving the symptoms and the method for processing the image sequence remains unaltered  134 . However, if the physiology is not improving, a lower aim peak value for the simulator sickness propensity value is calculated  136 . A more aggressive method for processing the image sequence is then selected  138  and all future digital image sequence clips with values higher than the aim propensity value are altered  130  to further reduce the propensity for sickness.  
         [0052]    Returning to step  122 , if the viewer does not signal the onset of sickness, the sickness flag is checked  140 , and if it is set, a higher aim peak value is set  142 . A less aggressive method for processing the image sequence is selected  144 . The image is then processed  130  and displayed  114 . If on the other hand, the sickness flag is not set, the image display is continued.  
         [0053]    An alternative embodiment of the present invention is shown in FIG. 8 which includes a user interface  152 , and a video capture device  150 , such as an electronic video camera or a film scanner, or a video generation device.  
         [0054]    The user interface  152  can be any text or image display capable of displaying a number that provides an indication of the likelihood that the video clip will induce motion sickness within a targeted video clip. The user interface  152  may be incorporated in the image display  14  that allows the viewer to view the image sequence and to provide the system feedback on its editing process.  
         [0055]    [0055]FIG. 9 shows a flow chart of the actions performed by the system shown in FIG. 8. Referring to FIG. 9, the viewer selects  154  an image sequence for editing. Next, the viewer indicates  156  the display characteristics. The viewer then indicates the user population which is used to determine  158  user sensitivity to simulator sickness. Using this value, the system sets  160  an aim peak value representing the propensity of the system to cause simulator sickness. The propensity of the image sequence to cause sickness is then calculated  162 . This value is displayed  164  to the viewer. If the viewer is comfortable with this value the viewer may decide  166  to save the image sequence without further modification. The system then saves the calculated values  170  and images  168  to an output file. If the user is not comfortable with the value, the user can apply  172  image processing to reduce the propensity of the image sequence to produce motion sickness. The propensity of image sequence to produce motion sickness is again calculated  162  and the process repeats.  
         [0056]    Once the viewer selects an image sequence for analysis, the viewer interface screen  156  such as the one shown in FIG. 10 can then be displayed. This display screen allows the viewer to see a series of thumbnails  180  that indicate different clips of video within the image sequence. The viewer interface screen  182  also shows a current selection  184  for the final display on which the digital image sequence will be viewed. The viewer may activate this menu to select another display system or to change the characteristics of the target display. The viewer selects the display characteristics, selects a viewer group to indicate viewer sensitivity and set an aim peak value for a sickness propensity value. By changing this selection, the viewer can modify relevant display characteristics such as the horizontal and vertical size of the display, the viewing distance to the screen, and whether the display is a stereoscopic display screen or not.  
         [0057]    The viewer interface also provides a display  186  of the current viewer population selected. The viewer may then modify the viewer population for which the video image sequence is being designed. As an example, the viewer may select a viewer population such as European males or Asian females. Based on data collected about individuals in these populations, the proportion of people in this population likely to experience motion sickness is estimated as a function of the maximum propensity of the digital image sequence to induce sickness on the selected display. This value is obtained by performing a look up of the maximum of the time-weighted average of the digital image sequence propensity value to determine subjective data collected in previously conducted experiments with groups from these populations. Based on this lookup, a value indicating the proportion of individuals who are likely to experience sickness may be generated and reported to the viewer of the software.  
         [0058]    A measure of the propensity of the digital image sequence to induce sickness or the proportion of individuals in the selected population who are likely to experience sickness is then calculated. A method for calculating the propensity of the image sequence to produce motion sickness has already been discussed and is shown in FIG. 7.  
         [0059]    This value is then displayed. The value may be presented to the viewer in a number of ways. One potential display of this information is shown as a sickness profile  188  in the example viewer interface depicted in FIG. 10. As already discussed, the interface shown in FIG. 10, may include a view of key image frames in the image sequence. The sickness profile is a time varying trace  188  of the propensity of the video to produce motion sickness. The display may also include an overall estimate  190  of the proportion of people who are likely to experience sickness.  
         [0060]    If the viewer decides that the stimulus for motion sickness is inappropriate after viewing the video and/or viewing the sickness propensity measure or the estimate of the proportion of individuals likely to experience negative symptoms, they may alter the current motion clip or produce a more desirable motion sequence.  
         [0061]    Many editing tools may be provided to the viewer of this system. These tools may include one or all of the following:  
         [0062]    a tool to alter the rate of motion and acceleration in the video by interpolating or integrating frames in the video, effectively reducing or increasing the perceived speed of action within the video;  
         [0063]    a tool to apply spatial filtering or contrast changes to the imagery to reduce or increase the number and the contrast of edges in the image sequences, especially near the edges of the display;  
         [0064]    a tool to indicate the region of focus within the video, and then apply spatial filtering or contrast changes away from this region of focus to reduce or increase the number and the contrast of edges in the video;  
         [0065]    a tool for replacing peripheral portions of the video with a uniform area, effectively reducing the field of view of the display system;  
         [0066]    a tool to allow the viewer to re-order scenes that have a high stimulus for motion sickness, interspersing these frames with still frames to reduce the onset of motion sickness;  
         [0067]    a tool to select another motion clip with a different level of stimulus for motion sickness in place of the current clip;  
         [0068]    a tool to remove portions of particularly provocative scenes, reducing the time duration of provocative scenes such that the likelihood of the onset of motion sickness is reduced;  
         [0069]    a tool to remove the stereo information from the scenery, copying the information that would be presented in one stereo channel to both stereo channels;  
         [0070]    a tool for adding noise or another distracting stimulus to the video information in order to reduce the perceived contrast of edges in the scene and reduce the perceived speed of motion of the video;  
         [0071]    a tool for adding a fixed frame of reference to the imagery, such as a stable horizon line or aircraft airframe on which the viewer can fixate to reduce the perception of self motion;  
         [0072]    if the imagery is generated, the maximum camera velocity and acceleration may be limited.  
         [0073]    As these edits are made to the video sequence, the estimate of motion sickness may be updated to reflect these changes. The viewer may interact with this system to produce one or more videos with different propensities to produce the onset of motion sickness.  
         [0074]    Once the viewer has completed editing the video, the system then allows the director to output the resulting data. The system may also allow the viewer to output values that were calculated by the system. These may include the raw motion vector data, the velocity information, the acceleration information, and/or the propensity for motion sickness profile data in a format that accompanies the video information. This information may then be further utilized by a display system, such as either of the systems disclosed earlier.  
         [0075]    While the system described here is a motion image editing system, one skilled in the state of the art will realize that this system could be embedded into an advanced digital video capture device, such as a digital video camera. In such a configuration, a videographer could capture a scene, review the scene and the data provided on the likelihood of the system to produce simulator sickness and then immediately decide to capture the scene again in a way that would alter the likelihood of the onset of motion sickness.  
         [0076]    The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.  
       PARTS LIST  
       [0077]    [0077] 10  storage device  
         [0078]    [0078] 12  digital image processor  
         [0079]    [0079] 14  image sequence display system  
         [0080]    [0080] 16  viewer input device  
         [0081]    [0081] 18  receive characteristics step  
         [0082]    [0082] 20  determine likelihood of sickness step  
         [0083]    [0083] 22  select highest vection path step  
         [0084]    [0084] 24  display image sequence step  
         [0085]    [0085] 26  provide viewer selection step  
         [0086]    [0086] 28  screen  
         [0087]    [0087] 30  text  
         [0088]    [0088] 32  list of selections  
         [0089]    [0089] 34  viewer selection step  
         [0090]    [0090] 36  select sequence step  
         [0091]    [0091] 38  use input device step  
         [0092]    [0092] 40  screen  
         [0093]    [0093] 42  text  
         [0094]    [0094] 44  list of selection  
         [0095]    [0095] 46  display step  
         [0096]    [0096] 48  obtain preference step  
         [0097]    [0097] 50  select sequence step  
         [0098]    [0098] 52  physiological response sensor  
         [0099]    [0099] 54  viewer profile source  
         [0100]    [0100] 56  retrieve information step  
         [0101]    [0101] 58  determine viewer propensity towards motion sickness  
         [0102]    [0102] 60  set peak value step  
         [0103]    [0103] 64  analyze time sequence step  
         [0104]    [0104] 66  perform test step  
         [0105]    [0105] 68  set value to zero step  
         [0106]    [0106] 70  determine speed step  
         [0107]    [0107] 72  determine camera acceleration step  
         [0108]    [0108] 74  transform edge motion vector step  
         [0109]    [0109] 76  determine point of gaze step  
         [0110]    [0110] 78  sum motion vector lengths step  
         [0111]    [0111] 80  compute average step  
         [0112]    [0112] 82  apply weighting step  
         [0113]    [0113] 84  determine stereo step  
         [0114]    [0114] 86  set weighting constant to greater than one step  
         [0115]    [0115] 88  set weighting constant to one step  
         [0116]    [0116] 90  multiply by weighting factor step  
         [0117]    [0117] 92  perform test step  
         [0118]    [0118] 94  set environment weight to greater than one step  
         [0119]    [0119] 96  set environment weight to one step  
         [0120]    [0120] 98  multiply step  
         [0121]    [0121] 100  set time constant step  
         [0122]    [0122] 102  computer weighted average time constant step  
         [0123]    [0123] 104  calculate propensity measure step  
         [0124]    [0124] 106  determine if propensity is higher than peak value step  
         [0125]    [0125] 108  select technique step  
         [0126]    [0126] 110  apply technique step  
         [0127]    [0127] 112  capture viewer base-line physiology step  
         [0128]    [0128] 114  display information step  
         [0129]    [0129] 116  measure viewer pallor  
         [0130]    [0130] 118  monitor viewer input device  
         [0131]    [0131] 120  measure change in physiology step  
         [0132]    [0132] 122  viewer signals step  
         [0133]    [0133] 124  determine if flag is set step  
         [0134]    [0134] 126  set flag step  
         [0135]    [0135] 128  chose alteration step  
         [0136]    [0136] 130  alter sequence step  
         [0137]    [0137] 132  determine physiology is improving step  
         [0138]    [0138] 134  do not alter method step  
         [0139]    [0139] 136  lower aim value step  
         [0140]    [0140] 138  select more aggressive method step  
         [0141]    [0141] 140  check flag step  
         [0142]    [0142] 142  set higher aim value step  
         [0143]    [0143] 144  select less aggressive method step  
         [0144]    [0144] 150  video capture device  
         [0145]    [0145] 152  user interface  
         [0146]    [0146] 154  select image sequence step  
         [0147]    [0147] 156  indicate display characteristics step  
         [0148]    [0148] 158  determine user sensitivity step  
         [0149]    [0149] 160  set aim peak step  
         [0150]    [0150] 162  calculate propensity to cause sickness step  
         [0151]    [0151] 164  display value step  
         [0152]    [0152] 166  decide to save step  
         [0153]    [0153] 168  save images step  
         [0154]    [0154] 170  save calculated values step  
         [0155]    [0155] 172  apply image processing step  
         [0156]    [0156] 180  thumbnails  
         [0157]    [0157] 182  viewer interface screen  
         [0158]    [0158] 184  current selection  
         [0159]    [0159] 186  current viewer population display  
         [0160]    [0160] 188  sickness profile  
         [0161]    [0161] 190  estimate of the proportion of people likely to get sick