***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: This paper describes an investigation of the types of problems that may be experienced by  Virtual Reality ( VR ) users .  Initial concerns have been voiced about various issues concerning the design of VR equipment , particularly the physical ergonomics of head-mounted displays ( HMDs ) and h and -held input devices , and the problems associated with display resolution and lags . This study investigated a number of VR users ' perceptions of the types of physical ergonomics issues  that they were aware of when participating in a number of different virtual environments ( VEs )  , using different VR systems .  Several different methods were employed , including question naires , body mapping , user observation and interviews . Issues highlighted as either causing participants discomfort or interfering with their experience of the VE were : discomfort from static posture requirements , general discomfort from wearing the HMD , difficulty becoming accustomed to 3D h and held input devices , dissatisfaction with deficits in the visual display and fear of getting ' tangled ' in connecting cables . The implication s of these findings for developers , implementers and users of VR are discussed Although head-mounted displays ( HMDs ) are ideal devices for personal viewing of immersive stereoscopic content , exposure to VR applications on them results in significant discomfort for the majority of people , with symptoms including eye fatigue , headaches , nausea , and sweating . A conflict between accommodation and vergence depth cues on stereoscopic displays is a significant cause of visual discomfort . This article describes the results of an evaluation used to judge the effectiveness of dynamic depth-of-field ( DoF ) blur in an effort to reduce discomfort caused by exposure to stereoscopic content on HMDs . Using a commercial game engine implementation , study participants report a reduction of visual discomfort on a simulator sickness question naire when DoF blurring is enabled . The study participants reported a decrease in symptom severity caused by HMD exposure , indicating that dynamic DoF can effectively reduce visual discomfort Background Virtual reality ( VR ) has recently been explored as a tool for neurorehabilitation to enable individuals with Parkinson ’s disease ( PD ) to practice challenging skills in a safe environment . Current technological advances have enabled the use of affordable , fully immersive head-mounted displays ( HMDs ) for potential therapeutic applications . However , while previous studies have used HMDs in individuals with PD , these were only used for short bouts of walking . Clinical applications of VR for gait training would likely involve an extended exposure to the virtual environment , which has the potential to cause individuals with PD to experience simulator-related adverse effects due to their age or pathology . Thus , our objective was to evaluate the safety of using an HMD for longer bouts of walking in fully immersive VR for older adults and individuals with PD . Methods Thirty-three participants ( 11 healthy young , 11 healthy older adults , and 11 individuals with PD ) were recruited for this study . Participants walked for 20 min while viewing a virtual city scene through an HMD ( Oculus Rift DK2 ) . Safety was evaluated using the mini-BESTest , measures of center of pressure ( CoP ) excursion , and question naires addressing symptoms of simulator sickness ( SSQ ) and measures of stress and arousal . Results Most participants successfully completed all trials without any discomfort . There were no significant changes for any of our groups in symptoms of simulator sickness or measures of static and dynamic balance after exposure to the virtual environment . Surprisingly , measures of stress decreased in all groups while the PD group also increased the level of arousal after exposure . Conclusions Older adults and individuals with PD were able to successfully use immersive VR during walking without adverse effects . This provides systematic evidence supporting the safety of immersive VR for gait training in these population It has been reported that females are more susceptible to motion sickness than males . Supporting evidence is primarily based on retrospective survey question naires and self-reporting . We investigated if there is a gender difference in motion sickness susceptibility using objective and subjective measurements under controlled laboratory conditions . Thirty healthy subjects ( 14 males and 16 females ) between the ages of 18 - 46 years were exposed to  Coriolis cross-coupling stimulation , induced by 120 degrees /s yaw rotation and a simultaneous 45 degrees pitch forward head movement in the sagittal plane every 12 seconds . Cutaneous forearm and calf blood flow , blood pressure , and heart rate were monitored . Graybiel 's diagnostic criteria were used to assess sickness susceptibility before and after motion exposure . Golding and Kerguelen 's scale was used to assess the severity of symptoms during motion exposure . A significant ( p<0.01 ) increase of forearm and calf blood flow during cross-coupling stimulation  was observed in both sexes . However , the subjective symptoms rating and blood flow measurements indicate that there was no significant difference between male and female subjects . Our data also suggests that females may be more inclined to admit discomfort as indicated by their responses to a survey of motion sickness history prior to the experiment Stroke and traumatic brain injury affect an increasing number of people , many of whom retain permanent damage in cognitive functions . Conventionally , cognitive function has been assessed by a paper-based neuropsychological evaluation . However these test environments differ substantially from everyday life . This problem can be overcome by using virtual reality ( VR ) to objective ly evaluate behaviors and cognitive function in simulated daily activities . With our virtual shopping simulation , we compared people who had undergone a stroke with control participants  in an immersive VR program that used a head-mounted display ( HMD ) . We evaluated user satisfaction with the tests , complications , and the user interface . Significant differences were consistently found between the stroke group and the control group for the following tasks : stage 1 performance index , interaction error ; stage 2 delayed recognition memory score , attention index ; and stage 3 executive index ( p < 0.001 ) . Perceptive dysfunction , visuospatial dysfunction , level of computer experience , and level of education affected the performance of the stroke group . The frequency of complications in the stroke group , calculated using the cut-off score for the Simulator Sickness Question naire , was 9.6 % for nausea , 41.9 % for oculomotor complications , and 25.8 % for disorientation . The frequency of complications between the stroke and control groups was not significantly different . Thirty-five percent of participants in the stroke group and 13 % in the control group reported difficulties with using the joystick . This computer-generated VR-based cognitive test shows promise in assessing cognitive function in patients with stroke . More refinements are needed in the user interface and the projection methods BACKGROUND Interactions between frequency and amplitude of latency in head-mounted displays ( HMDs ) are thought to affect  simulator sickness .  Many studies have linked system latency to subjective sickness , but recent research has found that at least with the case of inertia-based head tracking technology , latency is not a constant ; rather it varies systematic ally over time due to sensor errors and clock asynchronization . The purpose of this experiment was to further explore the relationship between frequency and amplitude of latency as they relate to subjective sickness experienced in an HMD . METHODS In a 2 ( frequency ) × 2 ( amplitude ) design , 120 subjects were r and omly assigned to 4  latency conditions . Frequency of latency was either 0.2 Hz or 1.0 Hz . Amplitude of latency was either 100 ms fixed or 20 - 100 ms varying . RESULTS A main effect of frequency of latency was found . Subjects reported greater sickness in the 0.2-Hz frequency conditions ( 39.0 ± 27.8 ) compared to the 1-Hz conditions ( 30.3 ± 17.0 ) . Additionally , 18 subjects withdrew their participation early in the 0.2-Hz conditions compared to 7 in the 1.0-Hz conditions . DISCUSSION In conclusion , frequency of latency appears to play a role in the experience of sickness in HMDs in both subjective reporting of symptoms and subject performance . The current study confirms results of earlier studies , finding that real motion around a frequency of 0.2 Hz is more sickening than other frequencies . Future work should continue to parse the effects of frequency and amplitude of latency in head-tracked HMDs . Kinsella A , Mattfeld R , Muth E , Hoover A. Frequency , not amplitude , of latency affects subjective sickness in a head-mounted display . Aerosp Med Hum Perform . 2016 ; 87(7):604 - 609 Virtual simulation sickness ( VSS ) is a form of visually induced motion sickness that can result fromimmersion in a virtual environment ( VE ) . As in their susceptibility to the sickness induced by real motion , womenhave been reported to be more susceptible than men to VSS , yet the reason for this difference is not known . The aim of the current study was to investigate the influence of themenstrual cycle on susceptibility to VSS in 16 naturally cycling women and to compare the responses of this group with control groups consisting of 1 ) 16 premenopausal women taking a combined monophasic oral contraceptive and 2 ) 16 men .  All female participants were immersed in a nauseogenic VE on days 5 , 12 , 19 , and 26 of their menstrual/pill cycle . These days were chosen because they fall in line with peaks and troughs of ovarian hormone levels . Menstrual cycle phase was confirmed by salivary estradiol and progesterone levels . A 4-week “ pseudo-cycle ” was assigned to the male participants . Hormone analysis revealed that 9 participants in the experimental group had been tested at the desired phases of their cycle . These participants exhibited a significant increase in susceptibility to VSS on day 12 of their cycle . The hormone analysis also showed that the cycles of the 7 remaining members of the experimental group had not precisely followed the expected pattern , and so these people had been tested on days that did not coincide with peaks and troughs of ovarian hormone levels . No consistent variation in susceptibility was observed over the cycle in these volunteers . In addition , no change in susceptibility was observed over the pill cycle of the oral contraceptive group nor over the pseudo-cycle applied to the male control group . The authors conclude that susceptibility to VSS varies over the menstrual cycle as a consequence of hormonal variation For those interested in using head-coupled PC-based immersive virtual environment ( VE ) technology to train , entertain , or inform , it is essential to underst and the effects this technology has on its users . This study investigated potential adverse effects , including the sickness associated with exposure and extreme responses ( emesis , flashbacks ) .  Participants were exposed to a VE for 15 to 60 min , with either complete or streamlined navigational control and simple or complex scenes , after which time measures of sickness were obtained . More than 80 % of participants experienced nausea , oculomotor disturbances , and /or disorientation , with disorientation potentially lasting > 24 hr . Of the participants , 12.9 % prematurely ended their exposure because of adverse effects ; of these , 9.2 % experienced an emetic response , whereas only 1.2 % of all participants experienced emesis . The results indicate that design ers may be able to reduce these rates by limiting exposure duration and reducing the degrees of freedom of the user 's navigational control . Results from gender , body mass , and past experience comparisons indicated it may be possible to identify those who will experience adverse effects attributable to exposure and warn such individuals . Applications for this research include military , entertainment , and any other interactive systems for which design ers seek to avoid adverse effects associated with exposure Background . Memory decline is a prevalent aspect of aging but may also be the first sign of cognitive pathology . Virtual reality ( VR ) using immersion and interaction may provide new approaches to the treatment of memory deficits in elderly individuals . Objective . The authors implemented a VR training intervention to try to lessen cognitive decline and improve memory functions . Methods . The authors r and omly assigned 36 elderly residents of a rest care facility ( median age 80 years ) who were impaired on the Verbal Story Recall Test either to the experimental group ( EG ) or the control group ( CG ) . The EG underwent 6 months of VR memory training ( VRMT ) that involved auditory stimulation and VR experiences in path finding . The initial training phase lasted 3 months ( 3 auditory and 3 VR sessions every 2 weeks ) , and there was a booster training phase during the following 3 months ( 1 auditory and 1 VR session per week ) . The CG underwent equivalent face-to-face training sessions using music therapy . Both groups participated in social and creative and assisted-mobility activities . Neuropsychological and functional evaluations were performed at baseline , after the initial training phase , and after the booster training phase . Results .The EG showed significant improvements in memory tests , especially in long-term recall with an effect size of 0.7 and in several other aspects of cognition . In contrast , the CG showed progressive decline . Conclusions . The authors suggest that VRMT may improve memory function in elderly adults by enhancing focused attention 
    Output:
    
VR sickness profiles were also influenced by visual stimulation , locomotion and exposure times .