Research Article Empirical Evaluation of Visual Fatigue ...downloads.hindawi.com/journals/jme/2013/521579.pdfspaces generated by stereoscopic images are arti cial spaces whicharedi

Hindawi Publishing CorporationJournal of Medical EngineeringVolume 2013 Article ID 521579 9 pageshttpdxdoiorg1011552013521579

Research ArticleEmpirical Evaluation of Visual Fatigue from Display AlignmentErrors Using Cerebral Hemodynamic Responses

Hanniebey D Wiyor and Celestine A Ntuen

Department of Industrial amp Systems Engineering North Carolina AampT State University 1601 East Market Street406 McNair Hall Greensboro NC 27411 USA

Correspondence should be addressed to Hanniebey D Wiyor hanniebeyyahoocom

Received 1 May 2013 Revised 16 October 2013 Accepted 28 October 2013

Academic Editor Nicusor Iftimia

Copyright copy 2013 H D Wiyor and C A NtuenThis is an open access article distributed under the Creative CommonsAttributionLicense which permits unrestricted use distribution and reproduction in anymedium provided the originalwork is properly cited

The purpose of this study was to investigate the effect of stereoscopic display alignment errors on visual fatigue and prefrontalcortical tissue hemodynamic responsesWe collected hemodynamic data and perceptual ratings of visual fatigue while participantsperformed visual display tasks on 8 ft times 6 ft NEC LT silver screen with NEC LT 245 DLP projectorsThere was statistical significantdifference between subjective measures of visual fatigue before air traffic control task (BATC) and after air traffic control task(ATC 3) (119875 lt 005) Statistical significance was observed between left dorsolateral prefrontal cortex oxygenated hemoglobin(l DLPFC-HbO

2) left dorsolateral prefrontal cortex deoxygenated hemoglobin (l DLPFC-Hbb) and right dorsolateral prefrontal

cortex deoxygenated hemoglobin (r DLPFC-Hbb) on stereoscopic alignment errors (119875 lt 005) Thus cortical tissue oxygenationrequirement in the left hemisphere indicates that the effect of visual fatigue is more pronounced in the left dorsolateral prefrontalcortex

1 Introduction

The visual system is a well-developed sensory organ thatinvolves effortless complex interaction between the visualorgan and the brain It involves physiological and a series ofhierarchical neural processes from the photoreceptors retinalganglion cells the lateral geniculate nuclei (LGN) of the tha-lamus and the visual cortices [1] The American OptometricAssociation [2] identified that prolonged use of the visualsystem can result in inefficient visual processing functionsgenerally called visual fatigue In line with that the AmericanAssociation of Ophthalmologist (AAO) diagnosed visualfatigue as an ophthalmological disease called asthenopia withthe medical diagnostic code of ICD-9 36813 with the sub-classifications shown in Table 1 [3 4]The last two digits of themedical code indicate the seriousness of the ophthalmologi-cal disease The larger the last two digits the more severe thesymptoms of the disease

Visual fatigue commonly arises when people view stereo-scopic motion images [5] In a stereoscopic image the viewerwatches two images corresponding to the right and left eyeswith convergence eye movement Based on individual char-acteristics and instrumentation issues conflicts can occur

between convergence or divergence eye movements and theaccommodation function thus causing visual fatigue [6] Oneof the major problems with stereoscopic displays is that astereoscopic display produces a mismatch between the focus(accommodation distance) and the fixation (convergencedistance) of human eyes Thus stereoscopic images maypresent different depth information to the accommodationand convergence functions Stereoscopic displays require thatthe viewer converges and accommodates at different depthplanes thus creating a conflict between the two visual mech-anisms [7] This problem is common in 3D display systemssuch as Head Mounted Displays (HMDs) and displays thatmake use of a lenticular lens Imbalanced visual informationmay be one of the reasons for the visual load and eventuallycan cause the visual fatigue associated with 3D images [8]Further Inoue and Ohzu [8] noted that the common causeof visual fatigue in a stereoscopic display is the fact that 3Dspaces generated by stereoscopic images are artificial spaceswhich are different from real spaces As a result the perceivedimages through 3D glasses do not really exist Okada et al[9] and Fukushima et al [10] showed that improvements ofimage quality when a stereoscopic system is used increase

2 Journal of Medical Engineering

Table 1 Ophthalmological classification of visual fatigue (asthe-nopia) with their respective symptoms

Ophthalmologicalmedical code Ophthalmological symptoms

ICD-9 3681 Subjective visual disturbancesICD-9 36810 Subjective visual disturbanceICD-9 36813 Asthenopia eye strain photophobia

the discrepancy of accommodation and convergence andmaycause increased visual fatigue For example in one of theirexperiments Kuze and Ukai [11] had participants playing avideo game using a stereoscopic HMD or monoscopic TVdisplay and found significantly greater increases in subjectiveratings of general discomfort nausea and headache afterusing the HMD compared to the increases observed with aconventional TV display

An issue not often discussed in stereoscopic displayresearch is alignment and calibration errors Three types ofalignment errors in optical systems are defined by Self [12]Vertical alignment error is an upward or downward tilt in theoptical axis of one image resulting in differences in verticalposition of an image Rotational alignment error is a tiltin one of the images with the degree of alignment errorincreasing from the center Lastly magnification differenceis an error due to the size difference between the left andright stereo pairs from the field of view Alignment errorshave two main sources [13] Firstly these are errors in opticsdue to a shift in the image placement of the left and rightstereo pairs These optical errors are due to either a shiftin rotation a difference in magnification or a difference inreduction Second filtration errors in photometry causedby the difference in luminance color contrast chromaticaberration or crosstalk (images switching back and forthbetween the eyes)The existing past studies have not explicitlyaddressed the issues of image alignment errors on the cerebralcortical responses and visual fatigue severity ratings Thisstudy investigates the effect of prolonged use of stereoscopicdisplay on visual fatigue and dorsolateral prefrontal cortexhemodynamic responses during visual display tasks

11 Contribution of This Paper The intellectual contributionof this paper can be realized in ophthalmological disease eti-ology optometry vision science and 3D devices and systemsSpecifically the neuroimaging of the brain in relation to visualfatigue can yield rich neurophysiologic data to objectively andclinically classify and diagnose onsets of visual fatigue

2 Methods

21 Participants This study included 21 males and 3 femalesrecruited from North Carolina Agricultural and TechnicalState University community Their ages ranged from 18 to 40years All participants self-reported no history of ophthal-mological diseases and optometric corrections Participantsrsquovisual acuity and color blindness score were limited to 2040

and 16 out of 22 points respectively and they were com-pensated for their participationTheUniversityrsquos InstitutionalReview Board approved all aspects of the research

22 Instrumentation and Data Acquisition The apparatus forthe study were a 8 ft times 6 ft NEC LT silver screen NEC LT 245DLP projectors NEC LT 245 polaroid glasses a 2210158401015840 158GHz099GB RAM Gateway DCDi Desktop a Snellen Chart anda Simulator Sickness Questionnaire (SSQ) a neurophysio-logical assessments and an ophthalmological questionnaireSeveral software systems were used for the study These wereAir Traffic Control Interface Model (ATCIM) CognitiveOptical Brain Imaging Studio (COBI) provided by fNIRSDevices LLC (2010) for the fNIRS Raw materials usedincluded 70 Isopropyl Alcohol Swabs Cotton Squares andAstroMed bandages

221 Simulator Sickness Questionnaire (SSQ) The SSQ asproposed by Kennedy et al [14] is comprised of four partsnausea rating oculomotor fatigue rating disorientation rat-ing and a total score rating It consists of thirty-two symp-toms and for each symptom a higher rating indicates that aparticipant experienced more symptoms The symptoms arerated as None = 0 Slight = 1 Moderate = 2 and Severe = 3

222 Functional Near Infrared Spectroscopy (fNIRS) fNIRSis a brain imaging device for exploring brain responses to avariety of stimulated cognitive and physical tasks in the fieldof cognitive neuroscience This device consists of an infraredlight source with a wavelength range of 650ndash850 nm into thehead and a detector that receives light after it has interactedwith the tissue [15] The emitted photons after interactingwith head tissues undergo two types of interaction namelyabsorption (loss of energy to the medium) and scattering[16ndash18] The spatial resolution in fNIRS is limited to approx-imately 5mm Researchers have shown that by placing theprobes on a Participantrsquos forehead fNIRS provides accuratemeasures of activities within the frontal lobe of the brainwhich are responsible for many high order cognitive func-tions such as memory and problem solving [15] The lightpassing through the frontal tissues is sufficiently low to allowfor tissue imaging at depths up to 20ndash30mm Deoxygenated(Hbb) and oxygenated (HbO

2) hemoglobin are the main

absorbers of near infrared light in tissues and they providerelevant markers of hemodynamic and metabolic changesassociated with neural activity in the brainThe levels of Hbband HbO

2measured are relative to the baseline only It is not

possible to arrive at absolute values of concentration usingfNIRS imaging on living samples Once the Hbb and HbO

2

levels are computed they are used to calculate the levels ofoxygenation (in 120583M) and values that may be approximatelytreated as percent changes in blood volume

223 Air Traffic Control Interface Model (ATCIM) The taskstimulus is an Air Traffic Control Interface Model (ATCIM)developed by Wiyor [19] and designed with LabView 81provided by National Instrument [20]The simulated testbedprovides a situation awareness (SA) environment similar

Journal of Medical Engineering 3

Figure 1 ATCM interface designed with LabView 91 softwareprovided National Instrument Wiyor [19]

to an ATC task domain The use of ATCIM as an ATCsimulator is specifically designed to allow for close experi-menter control over display features and task performancewhile providing a moderate degree of realism In the ATCIMdomain an operator perceives and responds to aircraft con-flict separation tasks which occur when two or more aircraftsare in self-separation violationThe separation violation is setto a loss of separation of 5NM laterally or 500 ft vertically orboth conditions can occur simultaneously [21] The ATCIMis shown in Figure 1

The ATCIM system consists of two main interfacesnamely the control setting interface and the dashboardinterface The control setting interface allows the user toselect inputs for the simulation These are (a) two closestaircraft color identifications (b) a color status bar in whichtwo mutually exclusive red and green colors appear withgreen for safe mode and red for crash mode (c) an alertdistance control that allows the user to preset the minimumsafe distance between two planes (d) a display time controlwhich allows for the user to input themaximum time allowedfor a participant to perceive and respond to a collision alert(e) a number of aircraft to monitor which allows the userto preselect the number of aircraft for the experiment (f)a collision alert used by the participants to respond beforecollision time and (g) an aircraft information-radii mode inwhich the plane path latitude longitude speed and bearingare displayed on the radii and move with the aircraft

The dashboard interface has an output section for datacollection during the simulation This consists of a 5NM(nauticalmiles) radius sector inwhich the number of aircraftsis selected to be monitored by the participants Based on thepredetermined mode selected from the setting section therequired output will be shown in the dashboard section ateach simulation run Each aircraft is characterized by trafficand conflict information Within the ATCIM the minimumsafe altitude warning distance is fixed to a default value

23 Experimental Procedures and Protocol The experimentwas conducted as completely randomized within participantdesign The experimental treatments are three stereoscopicalignment errors and each treatment was replicated twice

Table 2 Experimental independent variables their levels andmeasurement units

Factor Levels Measurements

Alignment errorsVertical shift 051015840

Rotational errors 0251015840Magnification differences 625

It should be noted that a particular treatment replication iscompleted before moving to the next treatment For exampleif the randomization order is vertical shift magnificationdifference and rotational error the vertical shift treatmentwill be replicated twice and each replication will last for 10minutes hence 20minutes for vertical shift as ATC1 followedby magnification difference two replications as ATC2 andlastly the rotational error with two replications as ATC3Table 2 contains the information on the independent variablelevels andmeasurement units for the experimentThe exper-imental treatments were characterized by cognitive loadingand task difficulty The cognitive loading was the number ofaircraft on the radar with separation conflictsThe number ofaircraft ran from low being 3 aircraft and high being 9 aircraft

Task difficulty was characterized by separation conflictslabeled as vertical horizontal combined horizontal andvertical and none respectively A highmaneuver (ATC3) hada maximum number of nine aircraft (high cognitive load)with either combined horizontal and vertical or none forseparation conflicts and a low maneuver (ATC1) had 2-3aircraft conflicts in the airspace

The independent variable was the stereoscopic alignmenterrors observed at three levels namely vertical shift rota-tional error and magnification difference For the verticalshift the focused images on the left and right retina were dis-placed by 051015840 the rotational error had the images displacedfrom each other in the left and right retina by 0251015840 andfor magnification difference an error was caused by 625enlargement in one image The two response measures inthe study were cerebral hemodynamic response and visualfatigue ratings The cerebral hemodynamic responses werecontinuous variables measured with fNIRS and visual fatiguesymptoms were subjective ratings measured by SSQ

Each participant was given an informed consent toread and sign Verbal explanations were provided to clarifyconcepts and terminologies The neurophysiological assess-ment and ophthalmological assessments survey question-naires were administered The ophthalmological survey wasused to ensure that the participants under 40 years hadno optometric andor ophthalmological symptoms Availablestudies have shown that after age 40 most people experiencethe onset of ocular-motor problems such as accommodationsand convergence [22 23] The National Eye Institute [24]estimates that currently more than 38 million Americansage 40 and older experience blindness low vision or an age-related eye disease such as age-related macular degeneration(AMD) glaucoma diabetic retinopathy or cataracts Thisis expected to grow to more than 50 million by year 2020[24] In addition a subjective neurological questionnaire wasadministered to participants for life styles andor accidentaldamage that might affect the brain electrophysiological data


Experimental treatments

Rotational error Magnification difference Vertical shift

Figure 2 Participant performing experimental tasks with various alignment error conditions

Each participant was assigned an alphanumerical iden-tification number instead of using their real names thesame identification number was also assigned to a particularrandomized experimental treatment in accordance with theIRB protocol The participantsrsquo foreheads were cleaned with70 Isopropyl Alcohol Swab and air-dried for two minutesThe fNIRS sensor pad was placed on the participantrsquos fore-head and held in place by a head band Participants wereintroduced and welcomed to the experimental station Theparticipants were then seated about 120 inches in front of the8 ft times 6 ft silver screen as shown in Figure 2 They were thengiven SSQ consisting of 32 symptoms to rate their perceptionof visual fatigue as none (0) slight (1) moderate (2) andsevere (3)

The participants proceeded to perform the ATC taskpresented in alignment error labeled as ATC1 After ATC1participants rated the SSQ symptoms Subsequently theyproceeded to perform the same ATC task but with a differentalignment error labeled as ATC2 The procedure wasfollowed by SSQ ratings Lastly the participants performedthe ATC task (labeled ATC3) under alignment errorsfollowed by SSQ ratings It should be noted that throughoutthe experiment participants were continuously asked ifthey were willing to continue the experiment The tasksinvolve continuous monitoring where the participantsvisually scanned the display to detect any two or moreself-separation violations The participants responded bypressing a ldquoCLICK BUTTONrdquo located at the interface of theATCIM if a violation was detected However if they detectedno self-separation violations no response was issued andafter 20 seconds the display refreshed itself to a new display

The self-separation violation was set to a loss of sep-aration of 5 nmi laterally or 500 ft vertically [25] Afterthe completion of each session participants were asked torate their perception of visual fatigue The participants wererequired to perform the experimental tasks as quickly and asaccurately as possible The average time for each experimentwas 1 hr 45mins inclusive of IRB briefing visual acuity testconducting the ophthalmological and neurological surveyquestionnaires performing the experiments and cleaningthe participants and debriefing them

24 Data Collection and Signal Preprocessing Four SSQinstruments were administered per participant after eachexperimental treatment labeled as BATC ATC1 ATC2 andATC3 For analyses the files were generated by conduct-ing frequency tallying each participantrsquos responses for eachexperimental treatment After obtaining the total numberof responses per symptom per treatment the total adjustedrating for each symptom was calculated as

Adjusted ratings for symptoms =sum3

119899=0119882119899119883119899

sum3

119899=0119883119899

(1)

where 119899 = 0 1 2 and 3 are the index counts for NoneSlight Moderate and Severe SSQ ratings of visual fatigue fora particular symptom119882

119899is the total rating for 119883

119899 and 119883

119899

has the values

119883119899=

1198830= 0 None1198831= 1 Slight1198832= 2 Moderate1198833= 3 Severe

(2)


Table 3 Descriptive statistics for hemodynamic responses

Alignment errors Statistic l DLPFC r DLPFCHbb HbO2 Hbb HbO2

Vertical shift119867max 1199 0955 1054 1597119867mean minus029 minus0625 minus025 minus0308119867stdev 0666 0608 0717 0781

Rotational error119867max 0916 1199 143 1561119867mean minus0204 minus0523 0068 minus0665119867stdev 0766 0656 0857 0873

Magnification difference119867max 0914 0928 0855 1514119867mean 0276 minus0563 0151 minus0413119867stdev 0641 0657 071 0764

The total weighted rating across all 32 symptoms per treat-ment was calculated as shown in

((

sum3

119899=0119882119899119883119899

sum3

119899=0119883119899

)

1198781

sdot sdot sdot

+(

sum3

119899=0119882119899119883119899

sum3

119899=0119883119899

)

11987832

) times (119873 = 24)minus1

(3)

where 119873 is total number of participants 1198781 1198782 11987832represent the types of symptoms rated

An fNIRS sensor pad was placed on the participantrsquosforehead specifically at the dorsolateral prefrontal cortex andheld in place by a head band The hemodynamic data wasrecorded using fNIRS (Model 1000 fNIR Devices LLC MDUSA) at a sampling rate of 100 kHz a frame rate of 500msand samples per voxels of 25 The data acquisition settingsincluded an LED drive current of 10mA an Analog-to-Digital (AD) gain of 1mA and an initial gain drift of 1 witha balance of 4000

There were two main hemodynamic responses measuredby fNIRS These responses were changes in oxyhemoglobinconcentration Δ119862HbO

2

(119905) and deoxyhemoglobin concentra-tion Δ119862Hbb (119905) from the 16 voxels The recordings cover thearea of dorsolateral prefrontal cortex (DLPFC) The DLPFCroughly corresponds to Broadman areas 9 and 46 and itcovers portions of the middle and inferior frontal gyri [26]These regions of interest for task execution in the prefrontalarea had been identified based on a previous fNIRS study byIzzetoglu et al [15] and based on a meta-analysis of otherneuroimaging studies performed by Cabeza and Nyberg[27] To reduce the data dimensionality participant averageswere computed using Microsoft Excel 2009 for both oxy-hemoglobin and deoxyhemoglobin concentration for the 16voxels asHbO2 (mean) andHbb(mean) respectively As indicatedby fNIR Devices LLC [28] the voxels 1 to 8 correspond tothe left (119897) DLPFC while voxels 9 to 16 correspond to right(119903) DLPFC For each of the two traditional hemodynamicvariables the mean value (119867mean) the maximum value(119867max) and standard deviation value (119867stdev) were computed

3 Data Analyses and Results

The data preprocessing consisted of two steps First eachof the dependent variables was preprocessed for outliersmissing values or nonresponses For the missing valuesthey were replaced by the computed average of the values[29] The second approach involved applying the appropriatesoftware and technique to each dependent variable to makeit suitable for statistical analysis A model adequacy checkwas performed to test for the three ANOVA assumptionsof normality independence and homogeneity of varianceIf the original data violated any of the assumptions anappropriate transformation was applied to the data until allthe assumptions weremetThemodel adequacy was analyzedwith statistical analysis software (SAS) [30] The descriptivestatistics for hemodynamic responses is summarized asshown in Table 3

31 Psychophysiological Ratings of Visual Fatigue Cronbachrsquosalpha reliability test was applied to the SSQ responses usingSAS [30] The Cronbach was evaluated based on participantsoverall SSQ scores for each ATC task session (alignmenterrors) Thus the dataset consisted of twenty-four observa-tions and four attributes representing BATC ATC1 ATC2and ATC3 A Cronbach alpha 0961 was obtainedThis showsstable responses considering 07 as the cutoff for acceptableresponse [31ndash34]

A paired 119905-test statistical technique (120572 = 005) was usedand the data was analyzed by SAS [30] At 5 signifi-cance level there was enough evidence to conclude that aprolonged use of stereoscopic display was likely to inducevisual fatigue as there was a significant difference betweenthe SSQ responses between before air traffic control task(BATC) and after air traffic control task (ATC 3) 119905 (23) =minus1527 119875 lt 005 An exploratory analysis revealed thattwenty-one of the thirty-two symptoms were pronouncedafter ATC3 This is shown in Figure 3 These observedsignificant symptoms include ache blurred vision boredomdifficult concentrating difficult focusing dizziness eye opendizziness eye closed double vision drowsiness eyestrainfaintness fatigue fullness of the head general discomfortheadache loss of appetite increased appetite mental depres-sion salivation increase salivation decrease and tearing


000050

100

150

200

250300

Ache Aware of breathingBlurred vision

BoredomBurning

Burping

ConfusionStrain

Sweating

TearingVertigo

Visual flashbacksVomiting

Desire to move bowels

Difficulty concentrating

Difficulty focusing

Dizziness eyes closed

Dizziness eyes open

Double vision

DrowsinessEyestrain

FaintnessFatigueFullness of the headGeneral discomfort

Headache

Increased appetite

Loss of appetite

Mental depression

Salivation decrease

Salivation increase

Stomach awareness

BATCATC3

Figure 3 A radial plot of weighted mean SSQ rated symptoms on BATC and ATC3 task sessions

Table 4 Pearson correlation coefficient using hemodynamic response variable

l DLPFC-Hbb l DLPFC-HbO2 r DLPFC-Hbb r DLPFC-HbO2

l DLPFC-Hbb 1l DLPFC-HbO2 037 1r DLPFC-Hbb 055 039 1r DLPFC-HbO2 minus043 044 064 1

Further one-way ANOVA analysis (120572 = 005) was con-ducted to determine the effect stereoscopic alignment errorson SSQ ratings At 5 level of significance there was enoughevidence to conclude that at least one of the stereoscopicalignment errors was different the one-way ANOVA results119865 (2 69) = 3538 119875 lt 005 A Tukey post ad hoc analysisrevealed that there was a significant difference betweenmagnification difference and vertical shift (119875 lt 005) andmagnification difference and rotational error (119875 lt 005)There was no significant difference between vertical shift androtational error

32 Tissue Hemodynamic Responses A one-way MANOVAstatistical technique (120572 = 005) was used to analyze the effectof display alignment errors on cerebral tissue hemodynamicresponses with SAS For any significance a Tukey post ad hocanalysis was conducted to reveal the significant differenceFor the hemodynamic responses the Hbb variable 119882 =0406 119875 lt 005 and HbO

2variable119882 = 0476 119875 lt 005 The

normality tests were violated As a result of significant vio-lations of the model adequacy checks by the hemodynamicdata the data underwent some transformations Varioustransformation approaches were applied to the hemody-namic response data and further analyzed for model ade-quacy check Eventually the box-cox transformation yielded

the best results The dataset was transformed by a power of13 (that is11988313) After the transformation Shapiro-Wilks testshowed that 119882 = 004 119875 = 065 for HbO

2variable 119882 =

0015 119875 = 0548 Levenersquos test for homogeneity of variance forHbb and HbO

2variables analyzed with ANOVA of squared

deviations from group mean had significant results for Hbb119865 (5 272) = 123 119875 = 0541 and HbO

2 119865 (5 272) = 074

119875 = 075There was a low to moderate correlation between the

hemodynamic variables All the variables were positivelycorrelated with the exception of (l) DLPFC-Hbb and (r)DLPFC-HbO

2 which had negative correlation between them

as shown in Table 4 This means that as an activity increasesin the left dorsolateral prefrontal cortex the less oxygen isdemanded in the right dorsolateral prefrontal cortex

From Table 4 119903 DLPFC-Hbb was positively correlatedwith r DLPFC-HbO

2 This means that an increase in activity

in the right dorsolateral prefrontal cortex requires an increasein oxygen demand We noted that r DLPFC-HbO

2was also

positively correlated with l DLPFC-HbO2 Thus any oxygen

requirement in the right dorsolateral prefrontal cortex resultsin equivalent increase in demand in the left dorsolateralprefrontal cortex (a positive correlation of 044) Furtherr DLPFC-Hbb has a positive correlation of 055 with lDLPFC-Hbb meaning that performance of visual activities


Table 5 ANOVA summary of significant effect of hemodynamic responses for the alignment errors using transformed data

Location Hemodynamicresponses Tukey post ad hoc analyses for alignment display errors (P lt 005)

r DLPFCDeoxygenatedhemoglobin

(Hbb)(Magnification difference and rotation error) and (magnification difference and vertical shift)

l DLPFCOxygenatedHemoglobin(HbO2)

(Magnification difference and rotation error) and (magnification difference and vertical shift)

Oxygenation(Hbb) (Magnification difference and rotation error) and (magnification difference and vertical shift)

is concurrent in both right and left dorsolateral prefrontalcortex

The one-way MANOVA results showedWilkrsquos Lambda =0924 119865 (8 132) = 066 119875 lt 005 Thus at 5 level ofsignificance there was enough evidence to conclude that thetransformed hemodynamic response as a composite scorewas significant Further at 5 level of significance therewas enough evidence to conclude that at least one of thestereoscopic alignment errors was different for l DLPFC-Hbb transformed dataset the ANOVA result 119865 (2 69) =010 119875 lt 005 for l DLPFC-HbO

2transformed dataset the

ANOVA result 119865 (2 69) = 015 119875 lt 005 and r DLPFC-Hbb transformed dataset the ANOVA result 119865 (2 69) = 109119875 lt 005 Tukey analyses for l DLPFC-Hbb l DLPFC-HbO

2

and r DLPFC-Hbb results are shown in Table 5

4 Discussion

It was possible to elicit tissue hemodynamic response andSimulator Sickness Questionnaire (SSQ) ratings based onvisual task in stereoscopic alignment errorsThe stereoscopicalignment errors had great impact on the SSQ responsesFrom the second to the third experimental sessions theparticipantsrsquo perceptual ratings of visual fatigue increasedfrom slight to moderate or moderate to severe The left dor-solateral prefrontal cortex was affected more than the rightdorsolateral prefrontal cortex The oxygenated hemoglobinand deoxygenated hemoglobin in the left dorsolateral pre-frontal cortex were significantly affected by the stereoscopicdisplay alignment error While in the right dorsolateralprefrontal cortex the stereoscopic display alignment errorhad an impact on only the deoxygenated hemoglobin Asobserved by Buxton et al [35] responses to stimuli changesresult in increase or decrease of regional cerebral blood flow(rCBF) to this localized brain region It increases with theincrease in demand for decision making processes The cor-tical tissue oxygenation requirement in the left hemisphereindicates that the effect of visual fatigue is more pronouncedin the left dorsolateral prefrontal cortex Using the oxy-genated hemoglobin deoxygenated hemoglobin blood vol-ume and oxygenation levels a 3D scatter plot for neuroimag-ing data comprising deoxygenated hemoglobin oxygenatedhemoglobin and oxygenation level was plotted as shown inFigure 4 Increases in the oxygenated hemoglobin resulted ina corresponding increase in the oxygenated levels This was

depicted by the upward movements toward the vertex of theoxygenation level and oxygenated hemoglobin variables

The same pattern was depicted in the right dorsolateralprefrontal cortex However for the right dorsolateral pre-frontal cortex the distribution was narrower than the leftdorsolateral prefrontal cortex The ATC tasks induced morecognitive processes in the left dorsolateral prefrontal cortexthan the right dorsolateral prefrontal cortex As a result ofcognitive load more energy was required by the brain witha corresponding oxygen requirement According to Hansen[36] the concentration of oxygen in the brain is about01 120583mol gminus1 of which 90 is in oxy-Hbb in brain capillariesThis concentration can support the normal oxygen consump-tion of about 35120583mol gminus1minminus1 for two seconds [37] For thisreason any increase in neural activity in the brain is followedby the rise in regional cerebral blood flow (CBF) [35] Oxygenis transported to neural tissue via oxygenated hemoglobin(oxy-Hbb) in the bloodThe demand for glucose and oxygenby neuronal tissues in a particular brain region may vary dueto particular processing requirements at a particular time

Increases in hemoglobin and oxygenation levels in leftdorsolateral prefrontal cortex mean that the left side of thebrain is more engaged with visiomotor cognitive processesthan the right side of the brain The continual engagementof the left brain may lead to mental fatigue The post adhoc analyses revealed that there were significant differencesbetween magnification error and rotational error and mag-nification error and vertical shift error However there wasno significant difference between rotational error and verticalshift error For the right hemisphere of the dorsolateralprefrontal cortex oxygenated hemoglobin blood volumelevel and oxygenation levels were significant Since mag-nification difference errors were significant we conducteda further analysis to identify likely points of visual fatigueThe hemodynamic responses revealed that significant differ-ences exist between left and right dorsolateral prefrontal inthe alignment errors in visual attention tasks 119865 (1 47) =0034 119875 lt 005 Generally oxygenation levels were increasedin both left and right dorsolateral prefrontal however itwas more pronounced in the left dorsolateral prefrontal Inthe left dorsolateral prefrontal the increased oxygenationlevels resulted from the corresponding increased oxygenatedhemoglobin and blood volume Contrasting to the left dor-solateral prefrontal oxygenated levels increased without any


15

1

05

0

minus05

minus15

minus1

minus2

minus25

1

1 1

105

05 05

050

0 0

0minus05

minus05minus05

minus05minus1

minus1minus1

minus1

minus15

minus15

minus15

minus15minus2

15

1

05

0

minus05

minus15

minus1

minus2

minus25

Oxy

gena

ted

leve

ls

Oxy

gena

ted

leve

ls

Oxygenated hemoglobin


Deoxygenated hemoglobin


(a) l DLPFC

3

2

1

0

minus1

minus2

minus3

151

1

105050

0

0minus05

10

minus05minus1

minus1minus1

minus1minus15

minus15minus2

minus2

3

2

1

0

minus1

minus2

15


Oxy

gena

ted

leve

ls

Oxy

gena

ted

leve

ls




2

minus32

(b) r DLPFC

Figure 4 Temporal patterns for hemodynamic responses for the dorsolateral prefrontal cortex for all the alignment errors during ATC tasks

blood flow to that region More interestingly the pronounce-ments in left dorsolateral prefrontal can be traced to the factthat all participants were right-handed

5 Conclusions

Regrettably it is well documented that the introduction ofthree-dimensional displays such 3D TV High-DefinitionMultimedia Interface (HDMI) desktop Head-Mounted Dis-play Helmet-Mounted Display and 3D glass into consumermarkets has resulted in the increase of oculist visits for visualcomplaints [38 39] From the empirical findings stereoscopicdisplay alignment errors can induce visual fatigue withaccompanying underpinning physiological effects associatedwith visual task performance Visual fatigue is likely toincrease the hemodynamic response in the left dorsolateralprefrontal cortex of the brain and delta band waves can beused to predict cognitive fatigue across all the occipital cere-bral cortex To improve 3D or stereoscopic display systemsfor minimum visual fatigue to the users the optical axessystem in display devices should be designed with minimummagnification difference and rotational error as these errorswere observed to be most prevalent 3D display designs withminimum magnification difference and rotational error aremore likely not only to reduce visual fatigue but also toincrease performances and satisfaction of the users such asaviators and flight pilots

Acknowledgments

This research was sponsored by Army Research Office (ARO)at North Carolina USA with the Grant no W911NF-07-R-0003-03 to Dr Celestine Ntuen as the PI The authors wouldlike to express their appreciation for the support Opinionsexpressed in this paper are not those of ARO organizationsand their people

References

[1] G C DeAngelis ldquoSeeing in three dimensions the neurophys-iology of stereopsisrdquo Trends in Cognitive Sciences vol 4 no 3pp 80ndash90 2000

[2] AmericanOptometric AssociationGuide to the Clinical Aspectsof Computer Vision Syndrome American Optometric Associa-tion St Louis Mo USA 1999

[3] National Center for Health Statistics International Classifica-tion of Diseases 9th Revision Clinical Modification PhysicianICD-9-CM Division of Data Services Hyattsville Md USA2003

[4] J E Sheedy J Hayes and J Engle ldquoIs all asthenopia the samerdquoOptometry and Vision Science vol 80 no 11 pp 732ndash739 2003

[5] K Ukai and P A Howarth ldquoVisual fatigue caused by viewingstereoscopic motion images background theories and obser-vationsrdquo Displays vol 29 no 2 pp 106ndash116 2008

[6] S Pastoor and M Wopking ldquo3-D displays a review of currenttechnologiesrdquo Displays vol 17 no 2 pp 100ndash110 1997

[7] E W Jin System Considerations for Optimizing Stereo ImageQuality Aptina Imaging Corporation 2011

[8] T Inoue and H Ohzu ldquoAccommodative responses to stereo-scopic three-dimensional displayrdquo Applied Optics vol 36 no19 pp 4509ndash4515 1997

[9] Y Okada K Ukai J S Wolffsohn B Gilmartin A Iijima andT Bando ldquoTarget spatial frequency determines the response toconflicting defocus- and convergence-driven accommodativestimulirdquo Vision Research vol 46 no 4 pp 475ndash484 2006

[10] T Fukushima M Torii K Ukai J S Wolffsohn and BGilmartin ldquoThe relationship between CAC ratio and indi-vidual differences in dynamic accommodative responses whileviewing stereoscopic imagesrdquo Journal of Vision vol 9 no 13 pp1ndash13 2009

[11] J Kuze and K Ukai ldquoSubjective evaluation of visual fatiguecaused by motion imagesrdquo Displays vol 29 no 2 pp 159ndash1662008


[12] H C Self ldquoOptical tolerances for alignment and image dif-ferences for binocular helmet-mounted displaysrdquo Tech RepAAMRL-TR-86-019 1986

[13] F L Kooi and A Toet ldquoVisual comfort of binocular and 3Ddisplaysrdquo Displays vol 25 no 2-3 pp 99ndash108 2004

[14] R S Kennedy N E Lane K S Berbaum and M G LilienthalldquoSimulator sickness questionnaire an enhanced method forquantifying simulator sicknessrdquo International Journal of Avia-tion Psychology vol 3 pp 203ndash220 1993

[15] K Izzetoglu S Bunce B Onaral K Pourrezaei and B ChanceldquoFunctional optical brain imaging using near-infrared duringcognitive tasksrdquo International Journal of Human-ComputerInteraction vol 17 no 2 pp 211ndash227 2004

[16] R D Rolfe ldquoThe role of probiotic cultures in the control ofgastrointestinal healthrdquoThe Journal of Nutrition vol 130 no 2pp 396Sndash402S 2000

[17] G Strangman D A Boas and J P Sutton ldquoNon-invasiveneuroimaging using near-infrared lightrdquo Biological Psychiatryvol 52 no 7 pp 679ndash693 2002

[18] B Chance S Nioka and Q Luo ldquoOptical system and methodfor non-invasive imaging of biological tissuerdquo Google patents1998

[19] H D Wiyor A Model of Dynamic Situation Awareness Indus-trial and Systems Engineering North Carolina Agriculture andTechnical State University Greensboro NC USA 2009

[20] J Travis and J Kring LabVIEW for Everyone Prentice HallUpper Saddle River NJ USA 2002

[21] V D Hopkins Human Factors in Air Traffic Control Taylor ampFrancis London UK 1995

[22] M Millodot and I Newton ldquoVEP measurement of the ampli-tude of accommodationrdquo British Journal of Ophthalmology vol65 no 4 pp 294ndash298 1981

[23] H A Stein and R M SteinThe Ophthalmic Assistant A Guidefor Ophthalmic Medical Personnel vol 6 Mosby St Louis MoUSA 1994

[24] National Eye Institute Why Fund the National Eye InstituteEye Diseases Health and Research Information US Departmentof Health and Human Services National Alliance for Eye andVision Research (NAEVR) Bethesda Md USA 2002

[25] M S Nolan Fundamentals of Air Traffic Control WadsworthPublishing Company Belmont Calif USA 1994

[26] A C Merzagora M T Schultheis B Onaral and M IzzetogluldquoFunctional near-infrared spectroscopy-based assessment ofattention impairments after traumatic brain injuryrdquo Journal ofInnovative Optical Health Sciences vol 4 no 3 pp 251ndash2602011

[27] R Cabeza and L Nyberg ldquoImaging cognition II an empiricalreview of 275 PET and fMRI studiesrdquo Journal of CognitiveNeuroscience vol 12 no 1 pp 1ndash47 2000

[28] fNIR Devices LLC FNIR Imager amp COBI Studio Manual fNIRDevices LLC Potomac Md USA 2010

[29] T Pang-NingM Steinbach andV Kumar Introduction to DataMining Pearson Addison Wesley Boston Mass USA 2006

[30] SAS Institute Inc CaryNC USA 2008[31] L J Cronbach ldquoCoefficient alpha and the internal structure of

testsrdquo Psychometrika vol 16 no 3 pp 297ndash334 1951[32] L Hatcher A Step-by-Step Approach to Using the SAS (R)

System for Factor Analysis and Structural Equation ModelingSAS Institute Cary NC USA 1994

[33] J Nunnaly Psychometric Theory McGraw-Hill New York NYUSA 1978

[34] J R A Santos L Lippke and P Pope ldquoPROC FACTOR a toolfor extracting hidden gems from a mountain of variablesrdquo inProceedings of the 23rd Annual SAS Users Group InternationalConference SAS Institute Inc Cary NC USA 1998

[35] R B Buxton K Uludag D J Dubowitz and T T LiuldquoModeling the hemodynamic response to brain activationrdquoNeuroImage vol 23 no 1 pp S220ndashS233 2004

[36] A Hansen ldquoDisturbed ion gradients in brain anoxiardquo Physiol-ogy vol 2 no 2 pp 54ndash57 1987

[37] O K Ames III ldquoConcerns about the lack of professionalismroot causes rather than symptoms must be addressedrdquo TheAmerican Journal of Trial Advocacy vol 28 pp 531ndash566 2004

[38] P Svensson ldquoA HEADACHE in 3-D companies push technol-ogy despite illnessesrdquo inNews amp Record p B5 Greensboro NCUSA 2011

[39] R M R Martınez R de la Escapita J de la Riva and A CF B Rodriguez Categorization of Fators Causing Athenopia inReserach Center Professors at the ITCJ by Reading with VDT AShared Experience Chih Ciudad Juarez Mexico 2009

International Journal of

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Active and Passive Electronic Components

Control Scienceand Engineering

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Submit your manuscripts athttpwwwhindawicom

VLSI Design



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Civil EngineeringAdvances in

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Electrical and Computer Engineering

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Advances inOptoElectronics


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The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of


Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014


Chemical EngineeringInternational Journal of Antennas and

Propagation




Navigation and Observation



DistributedSensor Networks



Table 1 Ophthalmological classification of visual fatigue (asthe-nopia) with their respective symptoms

Ophthalmologicalmedical code Ophthalmological symptoms

ICD-9 3681 Subjective visual disturbancesICD-9 36810 Subjective visual disturbanceICD-9 36813 Asthenopia eye strain photophobia

the discrepancy of accommodation and convergence andmaycause increased visual fatigue For example in one of theirexperiments Kuze and Ukai [11] had participants playing avideo game using a stereoscopic HMD or monoscopic TVdisplay and found significantly greater increases in subjectiveratings of general discomfort nausea and headache afterusing the HMD compared to the increases observed with aconventional TV display

An issue not often discussed in stereoscopic displayresearch is alignment and calibration errors Three types ofalignment errors in optical systems are defined by Self [12]Vertical alignment error is an upward or downward tilt in theoptical axis of one image resulting in differences in verticalposition of an image Rotational alignment error is a tiltin one of the images with the degree of alignment errorincreasing from the center Lastly magnification differenceis an error due to the size difference between the left andright stereo pairs from the field of view Alignment errorshave two main sources [13] Firstly these are errors in opticsdue to a shift in the image placement of the left and rightstereo pairs These optical errors are due to either a shiftin rotation a difference in magnification or a difference inreduction Second filtration errors in photometry causedby the difference in luminance color contrast chromaticaberration or crosstalk (images switching back and forthbetween the eyes)The existing past studies have not explicitlyaddressed the issues of image alignment errors on the cerebralcortical responses and visual fatigue severity ratings Thisstudy investigates the effect of prolonged use of stereoscopicdisplay on visual fatigue and dorsolateral prefrontal cortexhemodynamic responses during visual display tasks

11 Contribution of This Paper The intellectual contributionof this paper can be realized in ophthalmological disease eti-ology optometry vision science and 3D devices and systemsSpecifically the neuroimaging of the brain in relation to visualfatigue can yield rich neurophysiologic data to objectively andclinically classify and diagnose onsets of visual fatigue

2 Methods

21 Participants This study included 21 males and 3 femalesrecruited from North Carolina Agricultural and TechnicalState University community Their ages ranged from 18 to 40years All participants self-reported no history of ophthal-mological diseases and optometric corrections Participantsrsquovisual acuity and color blindness score were limited to 2040

and 16 out of 22 points respectively and they were com-pensated for their participationTheUniversityrsquos InstitutionalReview Board approved all aspects of the research

22 Instrumentation and Data Acquisition The apparatus forthe study were a 8 ft times 6 ft NEC LT silver screen NEC LT 245DLP projectors NEC LT 245 polaroid glasses a 2210158401015840 158GHz099GB RAM Gateway DCDi Desktop a Snellen Chart anda Simulator Sickness Questionnaire (SSQ) a neurophysio-logical assessments and an ophthalmological questionnaireSeveral software systems were used for the study These wereAir Traffic Control Interface Model (ATCIM) CognitiveOptical Brain Imaging Studio (COBI) provided by fNIRSDevices LLC (2010) for the fNIRS Raw materials usedincluded 70 Isopropyl Alcohol Swabs Cotton Squares andAstroMed bandages

221 Simulator Sickness Questionnaire (SSQ) The SSQ asproposed by Kennedy et al [14] is comprised of four partsnausea rating oculomotor fatigue rating disorientation rat-ing and a total score rating It consists of thirty-two symp-toms and for each symptom a higher rating indicates that aparticipant experienced more symptoms The symptoms arerated as None = 0 Slight = 1 Moderate = 2 and Severe = 3

222 Functional Near Infrared Spectroscopy (fNIRS) fNIRSis a brain imaging device for exploring brain responses to avariety of stimulated cognitive and physical tasks in the fieldof cognitive neuroscience This device consists of an infraredlight source with a wavelength range of 650ndash850 nm into thehead and a detector that receives light after it has interactedwith the tissue [15] The emitted photons after interactingwith head tissues undergo two types of interaction namelyabsorption (loss of energy to the medium) and scattering[16ndash18] The spatial resolution in fNIRS is limited to approx-imately 5mm Researchers have shown that by placing theprobes on a Participantrsquos forehead fNIRS provides accuratemeasures of activities within the frontal lobe of the brainwhich are responsible for many high order cognitive func-tions such as memory and problem solving [15] The lightpassing through the frontal tissues is sufficiently low to allowfor tissue imaging at depths up to 20ndash30mm Deoxygenated(Hbb) and oxygenated (HbO

2) hemoglobin are the main

absorbers of near infrared light in tissues and they providerelevant markers of hemodynamic and metabolic changesassociated with neural activity in the brainThe levels of Hbband HbO

2measured are relative to the baseline only It is not

possible to arrive at absolute values of concentration usingfNIRS imaging on living samples Once the Hbb and HbO

2

levels are computed they are used to calculate the levels ofoxygenation (in 120583M) and values that may be approximatelytreated as percent changes in blood volume

223 Air Traffic Control Interface Model (ATCIM) The taskstimulus is an Air Traffic Control Interface Model (ATCIM)developed by Wiyor [19] and designed with LabView 81provided by National Instrument [20]The simulated testbedprovides a situation awareness (SA) environment similar
























119899=0119882119899119883119899

sum3

119899=0119883119899

(1)



119899 and 119883

119899

has the values

119883119899=


(2)








((

sum3

119899=0119882119899119883119899

sum3

119899=0119883119899

)

1198781

sdot sdot sdot

+(

sum3

119899=0119882119899119883119899

sum3

119899=0119883119899

)

11987832

) times (119873 = 24)minus1

(3)




2







000050

100

150

200

250300


BoredomBurning

Burping

ConfusionStrain

Sweating

TearingVertigo




Difficulty focusing


Dizziness eyes open

Double vision

DrowsinessEyestrain


Headache

Increased appetite

Loss of appetite

Mental depression

Salivation decrease

Salivation increase

Stomach awareness

BATCATC3







2variable119882 = 0476 119875 lt 005 The



2variable 119882 =




2 119865 (5 272) = 074








2was also















2


4 Discussion






15

1

05

0

minus05

minus15

minus1

minus2

minus25

1

1 1

105

05 05

050

0 0

0minus05

minus05minus05

minus05minus1

minus1minus1

minus1

minus15

minus15

minus15

minus15minus2

15

1

05

0

minus05

minus15

minus1

minus2

minus25

Oxy

gena

ted

leve

ls

Oxy

gena

ted

leve

ls





(a) l DLPFC

3

2

1

0

minus1

minus2

minus3

151

1

105050

0

0minus05

10

minus05minus1

minus1minus1

minus1minus15

minus15minus2

minus2

3

2

1

0

minus1

minus2

15


Oxy

gena

ted

leve

ls

Oxy

gena

ted

leve

ls




2

minus32

(b) r DLPFC



5 Conclusions


Acknowledgments


References











































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation
































119899=0119882119899119883119899

sum3

119899=0119883119899

(1)



119899 and 119883

119899

has the values

119883119899=


(2)








((

sum3

119899=0119882119899119883119899

sum3

119899=0119883119899

)

1198781

sdot sdot sdot

+(

sum3

119899=0119882119899119883119899

sum3

119899=0119883119899

)

11987832

) times (119873 = 24)minus1

(3)




2







000050

100

150

200

250300


BoredomBurning

Burping

ConfusionStrain

Sweating

TearingVertigo




Difficulty focusing


Dizziness eyes open

Double vision

DrowsinessEyestrain


Headache

Increased appetite

Loss of appetite

Mental depression

Salivation decrease

Salivation increase

Stomach awareness

BATCATC3







2variable119882 = 0476 119875 lt 005 The



2variable 119882 =




2 119865 (5 272) = 074








2was also















2


4 Discussion






15

1

05

0

minus05

minus15

minus1

minus2

minus25

1

1 1

105

05 05

050

0 0

0minus05

minus05minus05

minus05minus1

minus1minus1

minus1

minus15

minus15

minus15

minus15minus2

15

1

05

0

minus05

minus15

minus1

minus2

minus25

Oxy

gena

ted

leve

ls

Oxy

gena

ted

leve

ls





(a) l DLPFC

3

2

1

0

minus1

minus2

minus3

151

1

105050

0

0minus05

10

minus05minus1

minus1minus1

minus1minus15

minus15minus2

minus2

3

2

1

0

minus1

minus2

15


Oxy

gena

ted

leve

ls

Oxy

gena

ted

leve

ls




2

minus32

(b) r DLPFC



5 Conclusions


Acknowledgments


References











































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation


















119899=0119882119899119883119899

sum3

119899=0119883119899

(1)



119899 and 119883

119899

has the values

119883119899=


(2)








((

sum3

119899=0119882119899119883119899

sum3

119899=0119883119899

)

1198781

sdot sdot sdot

+(

sum3

119899=0119882119899119883119899

sum3

119899=0119883119899

)

11987832

) times (119873 = 24)minus1

(3)




2







000050

100

150

200

250300


BoredomBurning

Burping

ConfusionStrain

Sweating

TearingVertigo




Difficulty focusing


Dizziness eyes open

Double vision

DrowsinessEyestrain


Headache

Increased appetite

Loss of appetite

Mental depression

Salivation decrease

Salivation increase

Stomach awareness

BATCATC3







2variable119882 = 0476 119875 lt 005 The



2variable 119882 =




2 119865 (5 272) = 074








2was also















2


4 Discussion






15

1

05

0

minus05

minus15

minus1

minus2

minus25

1

1 1

105

05 05

050

0 0

0minus05

minus05minus05

minus05minus1

minus1minus1

minus1

minus15

minus15

minus15

minus15minus2

15

1

05

0

minus05

minus15

minus1

minus2

minus25

Oxy

gena

ted

leve

ls

Oxy

gena

ted

leve

ls





(a) l DLPFC

3

2

1

0

minus1

minus2

minus3

151

1

105050

0

0minus05

10

minus05minus1

minus1minus1

minus1minus15

minus15minus2

minus2

3

2

1

0

minus1

minus2

15


Oxy

gena

ted

leve

ls

Oxy

gena

ted

leve

ls




2

minus32

(b) r DLPFC



5 Conclusions


Acknowledgments


References











































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation
















((

sum3

119899=0119882119899119883119899

sum3

119899=0119883119899

)

1198781

sdot sdot sdot

+(

sum3

119899=0119882119899119883119899

sum3

119899=0119883119899

)

11987832

) times (119873 = 24)minus1

(3)




2







000050

100

150

200

250300


BoredomBurning

Burping

ConfusionStrain

Sweating

TearingVertigo




Difficulty focusing


Dizziness eyes open

Double vision

DrowsinessEyestrain


Headache

Increased appetite

Loss of appetite

Mental depression

Salivation decrease

Salivation increase

Stomach awareness

BATCATC3







2variable119882 = 0476 119875 lt 005 The



2variable 119882 =




2 119865 (5 272) = 074








2was also















2


4 Discussion






15

1

05

0

minus05

minus15

minus1

minus2

minus25

1

1 1

105

05 05

050

0 0

0minus05

minus05minus05

minus05minus1

minus1minus1

minus1

minus15

minus15

minus15

minus15minus2

15

1

05

0

minus05

minus15

minus1

minus2

minus25

Oxy

gena

ted

leve

ls

Oxy

gena

ted

leve

ls





(a) l DLPFC

3

2

1

0

minus1

minus2

minus3

151

1

105050

0

0minus05

10

minus05minus1

minus1minus1

minus1minus15

minus15minus2

minus2

3

2

1

0

minus1

minus2

15


Oxy

gena

ted

leve

ls

Oxy

gena

ted

leve

ls




2

minus32

(b) r DLPFC



5 Conclusions


Acknowledgments


References











































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










000050

100

150

200

250300


BoredomBurning

Burping

ConfusionStrain

Sweating

TearingVertigo




Difficulty focusing


Dizziness eyes open

Double vision

DrowsinessEyestrain


Headache

Increased appetite

Loss of appetite

Mental depression

Salivation decrease

Salivation increase

Stomach awareness

BATCATC3







2variable119882 = 0476 119875 lt 005 The



2variable 119882 =




2 119865 (5 272) = 074








2was also















2


4 Discussion






15

1

05

0

minus05

minus15

minus1

minus2

minus25

1

1 1

105

05 05

050

0 0

0minus05

minus05minus05

minus05minus1

minus1minus1

minus1

minus15

minus15

minus15

minus15minus2

15

1

05

0

minus05

minus15

minus1

minus2

minus25

Oxy

gena

ted

leve

ls

Oxy

gena

ted

leve

ls





(a) l DLPFC

3

2

1

0

minus1

minus2

minus3

151

1

105050

0

0minus05

10

minus05minus1

minus1minus1

minus1minus15

minus15minus2

minus2

3

2

1

0

minus1

minus2

15


Oxy

gena

ted

leve

ls

Oxy

gena

ted

leve

ls




2

minus32

(b) r DLPFC



5 Conclusions


Acknowledgments


References











































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation





















2


4 Discussion






15

1

05

0

minus05

minus15

minus1

minus2

minus25

1

1 1

105

05 05

050

0 0

0minus05

minus05minus05

minus05minus1

minus1minus1

minus1

minus15

minus15

minus15

minus15minus2

15

1

05

0

minus05

minus15

minus1

minus2

minus25

Oxy

gena

ted

leve

ls

Oxy

gena

ted

leve

ls





(a) l DLPFC

3

2

1

0

minus1

minus2

minus3

151

1

105050

0

0minus05

10

minus05minus1

minus1minus1

minus1minus15

minus15minus2

minus2

3

2

1

0

minus1

minus2

15


Oxy

gena

ted

leve

ls

Oxy

gena

ted

leve

ls




2

minus32

(b) r DLPFC



5 Conclusions


Acknowledgments


References











































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










15

1

05

0

minus05

minus15

minus1

minus2

minus25

1

1 1

105

05 05

050

0 0

0minus05

minus05minus05

minus05minus1

minus1minus1

minus1

minus15

minus15

minus15

minus15minus2

15

1

05

0

minus05

minus15

minus1

minus2

minus25

Oxy

gena

ted

leve

ls

Oxy

gena

ted

leve

ls





(a) l DLPFC

3

2

1

0

minus1

minus2

minus3

151

1

105050

0

0minus05

10

minus05minus1

minus1minus1

minus1minus15

minus15minus2

minus2

3

2

1

0

minus1

minus2

15


Oxy

gena

ted

leve

ls

Oxy

gena

ted

leve

ls




2

minus32

(b) r DLPFC



5 Conclusions


Acknowledgments


References











































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation








































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation









Documents

Research Article Empirical Evaluation of Visual Fatigue ...downloads.hindawi.com/journals/jme/2013/521579.pdfspaces generated by stereoscopic images are arti cial spaces whicharedi