Research on Visual Fatigue When Playing Games

[Music] good afternoon everyone i am su yulin i'm a user research expert i'm a user experienced researcher from netease games it's a pity we could not present in person due to the threat of the code we both recognize the importance of health in daily life playing games is no exception and our talk concerns on players have too it's my pleasure to introduce our research on visual fatigue when playing games so here is the outline of this talk first i will briefly introduce some background on visual fatigue induced by viewing screens and in part two i will talk about two experiments we conducted to investigate

visual fatigue specifically when playing video games and finally part three i will explain the common causes of ice train and give some suggestions for game designers on how to avoid them now let's start with part one as we know looking at digital screens for long periods can cause a series of symptoms such as eye strain headaches variation dry eyes and so on this is also known as computer vision syndrome with the growing popularity of handheld and head mounted vr devices visual fatigue is now a very real threat to the health and gaming experience of our players many reports and literatures have also concluded that screen usage

might lead to eye strength especially for long durations we also hear about players complaining of eye discomfort after play sessions they wonder why some games lead to severe ice chain but not the other games they also try every way to relieve such discomfort since user research aims to provide better experience for users the health of our users eyes is an important concern for us we want to know how game playing leads to visual fatigue and how to relieve it so now we will show two studies we conducted to investigate eye strength for mobile games in study one our aim was to set up an assessment tool we wanted to find an objective and easy to implement indicator

and we hope it which is comparable across different things so by reviewing literatures we found several different methods including the first one is self-reporting which is easy conducting and comparable between different scenes but it is obviously a very subjective method and we also found the second one the optometric measurements which is absolutely objective but it is very difficult to conduct okay the last the third one psychophysiological methods which fully meets our requirements so by using psychophysiological indicators we measure one's physical states such as heart rate eye movement skin conductance and so on

then we use these indicators to infer about their mental states in this study we chose two indicators relating to visual sensitivity to infrared stream so here is the first indicator we use in this study that is cff or critical flicker frequency it is one of the indicators we use when measuring for eye strain here we shown is the device we use to measure cff an led light is mounted inside this device subjects watch through the eyepieces and they can adjust the frequency of the led now let's watch an animation please beware of flashing patterns ahead now let's watch this animation as we can

see the led flashes at the beginning as subjects increase the frequency they begin to perceive the flexion led as continuous when subjects feel the light is continuous we then record the frequency this frequency is the so-called cff or the critical flicker frequency let's watch the animation again now at the beginning it is flashing it's brushing and it's still flashing now also a bit stable but still i can feel the flashing okay no flashes anymore then in this case cff is at 30 hertz that means when the flashes increase the frequency of the flash increase to 30 hertz we can no longer feel the led expression if perceived as continuous to us

so we may wonder how does cff work as an indicator of visual fatigue let's look at an example before playing games i have a higher temporal sensitivity which means i am very good at discriminating the tiny flection flashing patterns so it needs a frequency as high as 40 hertz to make me perceive a steady and no flashing light any frequency lower than this threshold will be perceived as flashing for me then after i play games for two hours and i'm really tired my sensitivity decreases which means i can no longer discriminate the flashing precisely at this time a lower frequency at 35 hertz is enough for me to perceive as continuous

this means by comparing the cff before and after play sessions we can infer the severity of visual fatigue if cff decreases dramatically we might invert that the eyes must be tired in contrast if no such changes before and after playing games and string may not happen another psychophysiological indicator we use is contrast sensitivity which is the ability to distinguish between an object and the background a traditional method to measure context sensitivity is using a chart where the characters gradually fade from blank to gray as we can see in this graph for example when i am not tired i can distinguish

the slightly darker letter v from the background however when i am tired i can no longer see the letter v but can only see the much darker or another saiyan a higher contrast letter h so we can also invert the severity of visual fatigue or eye strain from the threshold changes of contrast sensitivity besides psychophysiological methods we also asked subjects to self-report on a scale of one to five points to measure various symptoms of vitro fatigue and to check whether the cff and contrast sensitivity indicators are valid or not in summary we have three indicators of einstein in this study the first one is cff which measures

temporal sensitivity cff decreases when one is tired second one is contrast sensitivity when one gets tired he or she can only discriminate a letter with higher contrast that is the threshold would be increased the third one is self-report it is straightforward now we move to the experiment the procedure was quite simple first we ask players to play games or watching videos for 20 minutes before and after the screen exposure we measure their cff their contrast sensitivity and also ask them to fill the self-report questionnaire and last by comparing by comparing the pre-test and post-test results

we can figure out to what extend players feel tired here are the results first the gray bar shows the cff or the critical flicker frequency before viewing screen remember that cff decreasing indicates players might have a lower sensitivity and we can infer that they may suffer eye strain let's come to the results as we can see after 20 minutes of screen exposure cff decreased more or less but we also noticed that playing games did not induce more severe visual fatigue than simply watching videos we also found that fps and racing game players suffer much than players of other game genres

we also found moderate correlations between cff contrast sensitivity and self-report which suggests that cff and cs threshold are effective indicators of visual fatigue so these are the insights of study 1. at the beginning of this study we aim to find out quantitative and valid indicators of eye strain throughout psychophysiological methods we found that cff or critical flicker frequency and contrast sensitivity they seem to be effective indicators of tiredness they can be useful for helping game designers determine whether in-game elements could lead to visual fatigue example players may complain that looting indoors induces discomfort when playing

battle royal games it is possible that the brightness of indoor lighting matters so we can compare between a bright and a diminished house throughout a b testing you can combine psychophysiological and self-report data to find out which condition will lead to eye strain for example the indicator shown here suggested that looting in the dim light immunity room that is the lower thing might easily lead to visual fatigue once we identify this risk factor we can try to eliminate the impact of such factors for example we can reduce the amounts of such rooms to avoid playing players cost too much time in such rooms or we can adjust the brightness and give

a better transition between darkness and brightness to provide better experience to the players and reduce the discomfort of visual fatigue or eye strain so in study one we found effective indicators these indicators including psychophysiological indexes which are objective and sensitive sensitive and self-report is very useful too and we also found that fps and racing game players suffered the most in study 2 we wanted to further understand the underlying mechanism and hope to shed light on how to relieve the tiredness so we chose fps and raising mobile games to further study visual fatigue and we also brought in optometric measurements in this study

by reviewing literatures we borrowed three optometric indicators first one when during the players playing games one may focus on the screen and they blink much less than usual this might lead to ice dryness so we use the indicator here breakup time or tbut to assess for dry eyes tbut shortening implied that eye dryness and discomfort might occur after or during the playing session second and the first indicators were related to accommodation ability of the eyes as we can see when focusing on distant objects ciliary muscles relaxed and the lens were flattened

in contrast when focusing on near point ciliary muscle contracted and the lens were thickened it might lead to ciliary muscle tired after a long duration when focusing on near points so we use two indicators the first is anterior chamber death or acd and the second accommodation power or ap to assess these symptoms change of these indicators implies that ciliary muscles are tired and might lead to blurry vision in summary we have three optometric measurements in this study the first one is tear procraptine which is a clinical assessment of eye dryness the second one is anterior chamber death when the eyes focus on near point for a

long duration anterior chamber death or acd might temporarily shorten suggesting that the cellular micro get tired and need rest the first one is accommodation power it is also related to focus adjusting when one gets tired the accommodation power will be impacted and the image cannot project to retina precisely and hence leading to player ratio by using these optometric measurements we can further understand the mechanism of visual fatigue when playing games the procedure for this study was very similar to study one it involves pre-game testing and one hour gameplay session and post game testing here shows the results of cff and

contrast sensitivity as expected cff and contrast sensitivity were impacted after each play session notice that the decrease of cff and increase of contrast sensitivity both means eyes get much tired after playing but we found no differences between playing fps and racing games the automatic measurements show some interesting results on one hand tier breakup time decreased after playing both games which was similar to results from previous studies this result implies that dry eyes and discomfort could occur after one hour exposure to the screens on the other hand anterior chamber depth

or acd and accommodation power or ap were impacted only in fps games but not in recent games as we can see here anterior chamber death and or the ecd it decreased suggests that after playing fps games ciliary muscle get tired temporarily and the time cost of accommodation increase indicated that accommodation power was also impacted ice needed a longer time for complete accommodation after playing fps games that is our eyes reflective and focusing powers are strongly affected by playing fps games it might be cause of in which or in the fps games it involves more camera training motions

the results of study 2 suggest that the effect of visual fatigue differs across different game genres the first tier breakup time might indicate the result of exposure to digital screen and it was a general effect acd and ap were specific to fps games this may be due to this genre demanding more rapid eye movements and frequently shift in focus distance so the ciliary muscle might get much tired after fps gaming and hence leading to the decrease of acd and impacted ap or the accommodation power which is just a fancy way of saying that the eye's ability to address focus may

be temporarily affected after playing fps or shooting games in study 2 we use optometric measurements to further shed light on the mechanism underlying visual fatigue fps games may be different from other game genres it requires lots of eye movement focus shift tiny discrimination it is much higher ratio demanding comparing to other game genres so playing shooting games for a long duration might lead to temporary impairments to visual function on the other hand the results of tier break up time also suggested that exposure to screens for a long time will also induce eye dryness even though not playing shooting games

okay then at last we came to some conclusions from our own studies and combined with review of other literatures we have summarized the common causes of visual fatigue this is the information that designers can use to build better games for our eyes so the number one cause of visual fatigue is high brightness here we use life after a survival mobile game as an example during alpha test players often complain that they feel eye strain when it rains in the game by ending by analyzing the graphic and comparing with other games we found that this was caused by raindrops that were too dense and too

bright so in the official launch version we cut down the density and the brightness of raindrops to improve users experience and we also receive good feedback on this iteration from our players and the second common cause of visual fatigue is low contrast obviously in a very low contrast condition it will make it very difficult to see and find useful information in the scene for example the same plan is much easier to identify and to tell the details in the right picture than in the left which with lower contrast in the left we can imagine that with two low contrast players will squint and have a hard time playing the game

and which would lead to faster visual fatigue and another factor is about fov and camera sensitivity it is another common cause of visual fatigue especially in shooting games this clip shows how a narrow fov plus high camera sensitivity can make players dizzy now let's watch this animation first fov with 90 degree it seems still acceptable for us right and with 140 degree fov it gets much better and much smoother but with a very narrow only 30 degree of fov it looks very dizzy for the players so of course we do not say that never use narrow fov in your games

but it is but it should be very careful to use such settings as we have seen a narrow fov with high camera sensitivity will lead to iron string quickly a compatible camera sensitivity if with fov would provide better experience for players and another factor relating to camera is steadiness let's take racing games for example as we can see from the clip the car position is not always the keep the same during players playing the games let's watch it again as we can see when the car slows down the car position is more closer to the players and when the car accelerates the car was far away from the players

the relationship between car position and speed is shown here when the car breaks the car gets closer to the players and when it accelerates the car move away this position changing is a frequently used trick to provide a stronger speed sensation to players and most of the situations this trick you use will not induce visual fatigue or visual discomfort to the players but in some other games or in the extreme conditions the car positions changes too obviously and too suddenly and this will make players feeling that the car is something like jumping and the camera is not steady and the camera they feel is very shaky and this will lead to visual discomfort

so what can we do to avoid or relieve visual fatigue when we developing our games first suggestion is conducting a b testing that use effective indicators of visual fatigue when designing new maps adding new elements or making any changes to your game you can use a b testing to identify elements that might cause visual fatigue and try to reduce its impact as i explained earlier cff and contrast sensitivity and self-report are very project friendly indicators of eye strain especially contrast sensitivity all you need is a conscious chart or a computer to conduct the test by combining various methods we can find out the risk factors and try to

eliminate them the second suggestion is providing options for players to set their preference by customizing displayed options such as brightness fov camera sensitivity players are more likely to find parameters suited to themselves we also can provide better experience by reminders and game settings during play sessions a so called 20 20 20 rule is recommended by eye doctors to prevent eye strain basically they suggest that every 20 minutes span using a screen one should try to look away at something that is 20 feet away for a total of 20 seconds return to game design we can recommend a red stop

when players have been playing for long durations especially for kids and youth players also we can utilize adaptive brightness features on phones or other devices to address the screen brightness according to the game content and environment lighting this will make a better experience of the eyes so in summary we talk about cff and contrast sensitivity are very effective psychophysiological indicators of visual fatigue they are objective easy to conduct and comparable using these indexes in a b test can help us identify risk factors of visual fatigue we also talk about some common causes leading to tiredness

such as brightness contrast a match foe and unsteady camera at last we can also do something when players playing games in-game settings such as reminding automatic brightness can relieve ice chain finally credits the work i showed today was done in collaboration with jay wong my colleague at netease games and we want to give sincere thanks to professor wang wang yoshung who from guangdong optometric association who provided automation measurement and data analysis for the second study that is all of my talk you can follow us on social media and thanks for coming and enjoy the rest of gdc thank you very much

hi that was super interesting and informative it's interesting because you're looking at the phenomenon in terms of discomfort that's your ultimate sort of variable you're trying to predict but the first thing that i thought of was a lot of times in game design you try to get people to notice things so for instance you want them to notice that there's a button they should press or they should notice a state change in a hud element and so if you think about tiredness not just as an end result but also as like cognitive load could be tiredness the more tired you make the player using the the variables related to eye fatigue they actually make it harder for you to be good at the game because it's harder for you to notice the things that you need to notice and so i'm i'm i'm it's interesting that while you're measuring for fatigue there's there's gameplay implications as well and that's why sound and other modalities can be effective but i've always struggled to find a way to to describe to people why adding more blinking lights and things like that are going to help with

noticing things and so i found your research fascinating because you actually gave me sort of some scientific underpinnings to display it so i guess my question is are you have you also thought about taking your research to how do we make people better at learning and playing and mastering these games through the sort of principles that you're teaching as opposed to or in addition to making their eyes less less tired at the end of the experience in my understanding are we when in the game settings we could uh as i mentioned at the last session of my talk well we think it is a good idea to introduce some uh eye happiness uh knowledge to the players and tell them uh uh for example uh every uh maybe every 20 minutes or every 30 minutes

of playing games we can recommend our rest to the players and if we and also we can use the we can monitor the time the players using uh per day or monitor the lighting environments of the players to provide a better experience to the players and also we think it is some politician and effect or kindness to the players especially for the kids and youth players to reduce the usage of the screens and we also we also found that from not only in our style deeper also in the other literatures are along a very long duration exposure to the screen is not

so health to the players no matter how old the players are so it's it's i think it is uh both responsibility for the game game designers and the police politicians or the governments yeah i hope i can answer your [Music] questions you