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Working memory for spatial construction in blind andsighted individualsMin-Sheng Chen a , Ching-Kai Huang a & Chih-Nan Wang aa Department of Industrial Engineering and Management , National Yunlin University ofScience and Technology 123 University Road , Section 3, Douliou, Yunlin 64002, Taiwan,Republic of ChinaPublished online: 14 Apr 2010.
To cite this article: Min-Sheng Chen , Ching-Kai Huang & Chih-Nan Wang (2010) Working memory for spatial constructionin blind and sighted individuals, Journal of the Chinese Institute of Industrial Engineers, 27:3, 199-208, DOI:10.1080/10170660903546723
To link to this article: http://dx.doi.org/10.1080/10170660903546723
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Journal of the Chinese Institute of Industrial Engineers
Vol. 27, No. 3, May 2010, 199–208
Working memory for spatial construction in blind and sighted individuals
Min-Sheng Chen*, Ching-Kai Huang and Chih-Nan Wang
Department of Industrial Engineering and Management, National Yunlin University of Science and Technology123 University Road, Section 3, Douliou, Yunlin 64002, Taiwan, Republic of China
(Received December 2008; revised March 2009; accepted October 2009)
Two experiments were conducted to examine the performance difference on the spatial workingmemory between blind and sighted subjects by manipulating auditory, visual, and tactile stimuli.The results indicated that blind subjects’ performance with tactile stimuli was no different to that of thesighted subjects with visual stimuli. Duration of visual impairment may be a factor influencingthe subjects’ performance. The late-blind subjects could form and organize the spatial informationby auditory and tactile modality based on their past visual experience. On the contrary, thecongenitally blind subjects restricted themselves to developing their mental imagery. Their performancewas worse than the late-blind subjects.
Keywords: blind individuals; auditory; tactile; working memory; mental imagery
1. Introduction
Blind individuals have to make adjustments inorder to live independently and productively.To interact with their environment efficiently,they develop superior abilities to make up for theloss of sight. In everyday life, spatial cognitionbenefits from the coordination of vision, audition,and touch. A person’s ability to discover, explore,mentally transform, and use relevant informationabout his or her surroundings enables the personto identify objects and navigate. Previous researchhas shown that visual experience is a critical factorin mental imagery abilities, and the current studyis interested in how blind individuals generatemental maps of spaces through touching andhearing. What is the difference between blindand sighted individuals with respect to spatialperception and memory?
1.1 Auditory modality
To compensate for their lack of visual ability,blind individuals develop a keener auditory ability.Blind individuals can identify a sound’s place oforigin more accurately than sighted individuals [4].Congenitally blind individuals can compensate forvisual loss by spatial hearing [10]. Blind and sightedindividuals are able to judge relative locations ofsounds with a similar correct rate. Researchers haveused semantic and physical encodings as stimulito examine the memory performance of blind andsighted individuals [12]. Results have shown that,whatever the encoding method, the performance of
congenitally blind subjects’ auditory memory isbetter than the performance of sighted individuals.Results also indicate that blind individuals canform mental models with their remaining senses.
In general, more so than sighted persons, blindindividuals rely on auditory input to acquireinformation about the world. Roder et al. [15]pointed out that younger blind individuals, or thelate blind, have better auditory sensation whencompared to sighted individuals. It seems that blindindividuals encode auditory information more effi-ciently than sighted ones. Research indicates thatthose who became blind early in life showedenhanced auditory abilities relative to sightedpersons as measured by tasks requiring attentionand memory [17]. A study showed that the occipitalcortex of blind individuals is organized in amodular fashion, just like in sighted individuals[13]. Researchers also suggested that the underlyingneural mechanism might result from making director indirect anatomical connections between theauditory and visual cortices. These connectionswere present in blind participants in the study,but rarely in sighted ones. It seems that blindindividuals take advantage of auditory sourcesof information.
1.2 Tactile modality
Researchers have devised a variety of tasks toexplore the process of mental imagery in blindindividuals [11]. In Marmor and Zabeck’s research[11], blind individuals were reported mentally
*Corresponding author. Email: [email protected]
ISSN 1017–0669 print/ISSN 2151–7606 online
� 2010 Chinese Institute of Industrial Engineers
DOI: 10.1080/10170660903546723
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rotating, moving, or twisting the target. Millar [12]asked blind and sighted children to move a pencilalong a plank on a fixed route, and the exper-imenter would tell subjects that they shouldstop moving at some danger point. Resultsindicated that sighted children formed the spatialinformation from their visual experience. The blindchildren used movement-based or self-referentcoding strategies to construct their spatial infor-mation. Blind children could control the directionand position while following a fixed route witha constant time period. Blind children, however,could no longer find the correct position if theroute and time period varied from previous ones.These results showed that blind children use a timesequence to construct spatial information. Theyproceeded along a certain route and memorizedthe route by touching objects along the route.However, blind children could not detect theoriginal route if researchers moved some of theobjects.
Visual experience is not necessary for pictureperception. However, it is certainly difficult forsubjects to interpret tangible pictures when the taskis novel [8]. Investigators used a tactile map tohelp blind individuals know their location. Ungaret al. [19] and Espinosa et al. [7] used tactile mapswith real streets to examine the performance ofblind individuals. Results demonstrated that blindindividuals used the tactile map to search the routeand that their performance was then as proficienton the actual route as the performance of sightedpersons. The blind individuals could form thespatial information on a 2-D tactile map whichhelped them sense orientation and mobility.
1.3 Spatial image memory
Blind individuals have a concept of visuo-spatialimagery. Some researchers have indicated thatindividuals use visual experience to form imagememory. Even if the person is congenitally blind,he or she can form mental imagery using auditoryor tactile senses. The performance of blind indivi-duals in spatial cognition can be as skillful as thatof sighted persons.
Arno et al. [1] used sounds to guide subjectsto move their index finger to memorize geometricfigures. This research found that blind individualscould use their auditory and tactile senses toconstruct spatial image memory. Blind individualsperformed better than did sighted individuals.However, the results also showed that sightedindividuals who had received long-term train-ing could perform as well as blind individuals.Blind individuals’ penetrative senses are notinherent [2,18].
Hollins [9] used auditory stimuli to help blindand sighted subjects construct an 8� 8 matrix figurewith black and white grids. The subjects neededto establish a spatial image composed of blackand white grids. Furthermore, his research used4� 4� 4 3-D matrix figures (represented by four4� 4 plane figures) to represent the stimuli. Theaims of this task were to examine visuo-spatialability, and the results showed that there wasno significant difference in accuracy between blindand sighted individuals in spatial imagery construc-tion. Thus, we know that spatial informationdoes not only rely on visual sense, but also relieson touching and hearing. Blind individuals withdifferent durations of visual deficiency had differentperformance. Late-blind individuals with longervisual experience performed better than the con-genitally blind. Results also showed that visualexperience helped blind individuals identify 2-Dfigures.
Several experiments similar to Hollins’ para-digm were conducted by Vanlierde and Wanet-Defalque [20]. He asked subjects to identify theplane symmetry. The results showed no differencein performance between the congenitally blind andlate-blind subjects. Furthermore, the blind subject’sperformance was not different from that of thesighted subject. Even congenitally blind subjectshad a certain ability to develop the spatial image.However, late-blind subjects memorize the blackgrids and identify the symmetry using a visualstrategy while the congenitally blind ones codethe black grid’s position with their fingers toconstruct relevant location information.
1.4 Mental imagery memory
Mental imagery can be defined as ‘‘seeing in themind’s eye.’’ People use mental imagery to helpfinish many tasks, and mental imagery generationis the ability to form visual images that requireperceiving, processing, and storing visual informa-tion. Although blind individuals had lost theirvisual abilities, they could generate mental imageryby touching and hearing.
Two alphabet letters (F and P) were manipulatedto examine themental imagery performance of blindindividuals [5]. The letters included normal patternsand mirror patterns. They were collocated bysix different rotational angles from 0� to 360�. Theexperimenter requested that blind individualstouch the stimuli and determine whether the alpha-bet was upright or not. Results indicated that if therotational angle was large, blind individuals neededmore time to make a determination. Reaction timeprogressively increases linearly from 0� to 180� and360� to 180�. Sighted and blind individuals have
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similar performance with mental rotation. Sight isnot the only factor essential for mental rotation.Researchers sometimes used language representa-tion to aid memorization of visual spatial mentaltasks [6].
Studies have tested blind individuals to deter-mine whether they have a mental imagerydeficiency. Mental imagery improves memory per-formance. Studying blind individuals helps identifythe contribution of compensatory senses for cogni-tive functions. Blind people may rely more heavilyon auditory and tactile information to hold spatialmemory. In addition, the duration of visual defi-ciency may be linked to visual experience and affectwhat mental imagery is built up.
The present study was designed to test theefficiency of spatial memory with auditory codingand tactile coding in the blind compared to sightedindividuals. We tested blind individuals and sightedones on two spatial memory tasks that requiredauditory/visual/tactile coding. A numerical track-ing task and an object tracking task were conductedin experiments 1 and 2, respectively. It washypothesized that no difference in performancebetween blind subjects and sighted ones would beexpected in these two tasks. However, highermemory performance by late-blind persons wouldbe predicted compared to the congenitally blind.
2. Experiment 1
2.1 Subjects
A group of 12 sighted subjects (mean age 23.6years, range 21–27 years, 5 females, right-handed),6 congenitally blind subjects (mean age 26.9 years,range 20–31 years, 4 females, right-handed) and6 late-blind subjects (mean age 30.2 years, range24–36 years, 1 female, right-handed) participatedin the study. The late-blind subjects had visualimpairment before the age of 15. All subjectsreported normal hearing and signed informedconsent forms.
2.2 Experiment materials
Numerical numbers were used as stimuli for thestudy. Auditory stimuli were presented with arecording machine, the visual ones with MicrosoftPowerPoint�, and the tactile ones with a foamboard (59 cm� 39 cm). Each number was repre-sented in a 4� 4 square matrix (Figure 1).
2.3 Design
Three factors were manipulated in this experi-ment: a between-subjects variable, visual ability
(able/disable); a within-subjects variable, set size(5/7/9); and the type of stimuli (visual, tactile/auditory). An additional between-subject variablewas the duration of visual disability. Congenitallyblind subjects’ duration of visual impairment wasover 25 years. The duration of visual impairmentfor late-blind subjects was under 15 years.
The blind subjects were asked to completetracking tasks of memorizing sequential numbersplayed audibly and presented tactilely. Sightedsubjects were requested to complete the sametasks presented audibly and visually.
2.4 Procedure
This experiment was to explore the performancedifference of numerical tracking on spatial memorybetween blind and sighted subjects. Using audiblestimuli, subjects were required to generate a mentalrepresentation of a 4� 4 square matrix. Five, seven,or nine numbers were played audibly. The numberswere spoken one by one to present the correspond-ing position in the 4� 4 matrix. The sequencewas from left to the right for row one, then for rowtwo, then for row three. Each number was spokenfor 3 s. The word ‘‘blank’’ was spoken if there wasno number in a particular cell of the matrix. Usingvisual stimuli, numbers were presented on a com-puter (Figure 2). Each number was also presented
Figure 1. Tactile materials of experiment 1 (sevennumbers).
7
4 5 6
3
2 1
Figure 2. Visual stimulations of experiment 1 (sevennumbers).
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for 3 s. Using tactile stimuli, numbers were pre-sented on a foam board with the experimenterleading the subjects to touch the numbers. Eachnumber was touched for three seconds.
Subjects were asked three questions aboutthe location of numbers, such as ‘‘which numberwas to the right of number 4?’’ (Figure 2). Subjectswere required to finish 36 trials in which the 18possible combinations of the three set sizes, twostimuli types, and three questions each appearedtwo times. Each trial was being counterbalancedat all levels. The accuracy rate was reportedand used as a dependent variable.
2.5 Results
The main effect differences of stimuli type( p5 0.001) and set size ( p5 0.001) were statisti-cally significant (Table 1). The visual ability differ-ence was not statistically significant. Stimuli typeeffect showed that sighted people’s visual perfor-mance was better than their auditory performanceand that blind subjects’ tactile performance wasbetter than their auditory performance (Figure 3).There was statistically significant interactionbetween set size and visual ability ( p¼ 0.026).The interaction effects (Table 1) indicated that theperformance of sighted subjects was more stable(Figure 4) than blind subject performance anddid not change significantly regardless of set sizechanges.
The congenitally blind and late blind may varyin performance based on the presence or absenceof former visual experience. The duration of visualimpairment was taken into account in this studyand the results are depicted in Table 2 and Figure 5.The late-blind subjects have steady performance onspatial memory performance with either auditoryor tactile stimuli. By contrast, the congenitallyblind have better performance with tactile stimulithan with auditory.
The main effect differences of stimuli type
and the set size were statistically significant,
p¼ 0.001 and p5 0.001, respectively. The interac-
tion of stimuli type and the duration of visual
Auditory Visual / Tactile0.6
0.7
0.8
0.9
Stimuli type
Blind
Sighted
Acc
urac
y ra
te
Figure 3. Accuracy rate for auditory and visual/tactilestimuli by blind and sighted subjects on a numericaltracking task.
Table 2. ANOVA for congenitallyand late-blind subjects of experiment 1.
Source F-value p-value
BetweenDI 2.666 0.134
WithinST 21.568 0.001*ST�DI 15.651 0.003*SS 14.412 0.001*SS�DI 1.594 0.228ST� SS 4.525 0.024*ST� SS�DI 0.582 0.568
Notes: DI – duration of visually imp-aired; ST – stimuli type; SS – set size.*p5 0.05.
0.6
0.7
0.8
0.9
Set size
Acc
urac
y ra
te
Sighted
Blind
5 7 97 9
Figure 4. Interaction of set size and visual ability ona numerical tracking task.
Table 1. ANOVA for blind andsighted subjects of experiment 1.
Source F-value p-value
BetweenVA 0.971 0.335
WithinST 18.670 0.001*ST�VA 0.007 0.936SS 9.509 0.001*SS�VA 3.951 0.026*ST� SS 1.837 0.171ST� SS�VA 2.310 0.111
Notes: VA – visual ability; ST –stimuli type; SS – set size.*p5 0.05.
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impairment was statistically significant ( p¼ 0.003).The interaction between stimuli type and set sizewas statistically significant ( p¼ 0.024). Figure 6shows that subject performance with auditorystimulus declined when the set size was increased.However, performance was not significantlyaffected by a change in set size when subjectsused a tactile modality.
3. Experiment 2
3.1 Subjects
Subjects were the same as in experiment 1.
3.2 Experiment materials
Auditory stimuli were played by sound recording,the visual stimuli were presented on a computer,and the tactile stimuli were handmade and placedon a flat board (59 cm� 39 cm) by the experi-menter. The tactile stimuli resembled 12 objects insmall scale including a department store, a hospital,an office building, a school, a park, a mosque,a housing complex, a temple, a pasture, a railroadstation, a pig pen, and a lighthouse (Figure 7).
3.3 Design
Three factors were evaluated in this experiment:a between-subjects variable, visual ability (blind/sighted); a within-subjects variable, set size (4/6);and stimuli type (auditory, visual/tactile). The blindsubjects were requested to memorize the locationof the objects.
3.4 Procedure
This experiment explored the performance ofobject tracking on spatial memory between blindsubjects and sighted ones. Six kinds of soundswere recorded to represent the objects so thatsubjects could recognize to which object a soundcorresponded.
For example, the sound to represent the hospitalwas an ambulance siren and the sound to representthe school was the ring of the class dismissal bell.Blind subjects were required to generate a mentalrepresentation of a 4� 4 square matrix. Four or sixmimic sounds of objects were played one by onefrom left to right by a recorder for the first rowof the matrix. The same procedure was followedfor the second, third, and fourth rows. Eachsound was played for 5 s. The word ‘‘blank’’ waspronounced instead of an object when there was noobject in a particular grid of the matrix.
For visual stimuli, hand-made objects wereplaced on the flat 4� 4 matrix board (Figure 8).
Figure 7. Objects in experiment 2. Left: resembling office building; Right: resembling pasture.
0.6
0.7
0.8
0.9
Auditory TactileStimuli type
Acc
urac
y ra
te
Congenital
Late
Figure 5. Interaction of stimuli type and duration ofvisual impairment.
0.5
0.6
0.7
0.8
0.9
1
5 7 9Set size
Acc
urac
y ra
te
Auditory
Tactile
Figure 6. Interaction of set size and stimuli type.
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Subjects were permitted to look at the objects for5 s one by one. For tactile stimuli, hand-madeobjects were placed on the flat board. Subjects wereled by the experimenter to touch the small-scaleobjects for 5 s one by one.
After the stimuli presentations, subjects wereasked four questions about the relative locationof the objects, such as how to get to the three-section compound from the railroad station (theanswer should be ‘‘go left two blocks and up twoblocks’’ (Figure 9)). Each trial had four questions.Subjects were required to finish four trials.
3.5 Results
Table 3 shows the results. The main effectdifferences of stimuli type ( p5 0.001) and set size( p5 0.001) were statistically significant. Therewas no significant difference in visual ability( p¼ 0.088). The interaction effects between stimulitype and set size were statistically significant( p¼ 0.008). There was no statistically significantdifference in the interaction between set sizeand visual ability ( p¼ 0.06).
The results also demonstrated that bothsighted and blind subjects perform worse withauditory stimuli compared to visual/tactile stimuli(Figure 10). Blind subjects had better performancewith a tactile modality versus an auditory modality
whereas sighted persons got a higher accuracyrate with a visual modality compared with anauditory modality.
Figure 11 shows that, when the set size wasincreased, blind subjects performed better thansighted persons did. Figure 12 indicates that subjectperformance declined dramatically using audi-tory stimuli when the set size was increased.
However, performance remained stable using atactile modality for blind subjects and a visualmodality for sighted persons.
Figure 13 reveals no statistically significantdifference between sighted subjects with a visualmodality and blind persons with a tactile modality.
0.3
0.4
0.5
0.6
0.7
0.8
Stimuli type
Blind
Acc
urac
y ra
teSighted
Auditory Visual / Tactile
Figure 10. Accuracy rate for auditory and visual/tactilestimuli by blind and sighted subjects on objecttracking task.
Table 3. ANOVA of the ratio ofcorrect position for sighted and blindsubjects.
Source F-value p-value
BetweenVA 3.184 0.088
WithinST 26.422 0.001*ST�B 2.675 0.116SS 44.674 0.000*SS�VA 3.922 0.060ST� SS 8.494 0.008*ST� SS�VA 2.124 0.159
Notes: VA – visual ability; ST –stimuli type; SS – set size.*p5 0.05.
Figure 8. The tactile materials of experiment 2 (example:six objects).
Rail-
road
station
Lighthouse
Pasture Temple
Three section
compound
Pig
house
Figure 9. Example of experiment 2 (example:six objects).
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Notably, sighted subjects’ performance changed
gradually from high to low accuracy as the set size
increased.Figure 14 shows that late-blind persons had
stable performance in both auditory and tactile
modalities, which are similar to the results
from experiment 1. By contrast, the performanceof the congenitally blind declined dramaticallybetween a tactile modality and an auditorymodality.
The duration of visual impairment was consid-ered in the analysis (Table 4). This study observedthat the main effects of object size were statisticallysignificant ( p¼ 0.016). Figure 15 showed that the
Table 4. ANOVA of the ratio ofcorrect position for congenitally andlate-blind subjects.
Source F-value p-value
BetweenDI 4.238 0.067
WithinST 3.893 0.077ST�DI 0.848 0.379SS 8.318 0.016*SS�DI 0.207 0.659ST� SS 2.049 0.183ST� SS�DI 6.639 0.028*
Notes: DI – duration of visually imp-aired; ST – stimuli type; SS – set size.*p5 0.05.
0.2
0.4
0.6
0.8
Set size
Acc
urac
y r
ate
Blind
Sighted
4 6
Figure 11. The performance of different set sizes withblind and sighted subjects.
0
0.2
0.4
0.6
0.8
1
4 6Set size
Acc
urac
y r
ate
Tactile of blind
Auditory of sighted Visual of sighted
Auditory of blind
Figure 13. Interaction of set size, visual ability, andstimuli type.
0.2
0.4
0.6
0.8
Set size
Auditory
Visual/Tactile
Acc
urac
y r
ate
4 6
Figure 12. Interaction of set size and stimuli type.
0.4
0.5
0.6
0.7
0.8
0.9
Auditory Tactile Stimuli type
Acc
urac
y r
ate
Congenital
Late
Figure 14. Accuracy rate for stimuli type and durationof visual impairment.
0.2
0.4
0.6
0.8
1
4 6Set size
Acc
urac
y r
ate
Auditory of congenital Tactile of congenital
Auditory of late Tactile of late
Figure 15. Interaction of set size, stimuli type, andduration of visual impairment.
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late-blind subjects had steady performance witheither auditory or tactile stimuli regardless of setsize changes. However, congenitally blind subjects’performance worsened dramatically using auditorystimuli when set size was changed from 4 to 6. Thecongenitally blind had better performance in tactilemodality.
4. General discussion
The purpose of this study was to examine perfor-mance differences on the spatial working memorybetween blind and sighted individuals. In experi-ment 1, blind subjects were requested to memorizethe locations of sequential numbers with auditoryand tactile modalities. Sighted subjects completedthe same tasks, but with auditory and visualmodalities. The results showed that blind subjects’performance with a tactile modality was notdifferent from the sighted subjects’ performancewith a visual modality. Compared with the visual/tactile modality, both blind and sighted subjectshad worse performance in auditory modality.This outcome may be attributed to a blind person’sprevious experience with a tactile modality.The performance for the blind with a tactilemodality is better than with an auditory modality.In addition, the results also showed that congeni-tally blind subjects could construct mental repre-sentations using a tactile modality. The results ofthis study agree with the research of Arno et al. [1].
In experiment 2, subjects were requested tomemorize the location of objects when the stimuliwere visual, auditory, and tactile modalities.The results indicated that blind subjects couldhandle spatial imagery among objects by a tactilemodality whereas sighted subjects could not do so.Sighted individuals rely on their visual modality tointeract with the environment and they perceiveinformation in the world with their eyes. In thisstudy, sighted and blind subjects may constructthe mental representations with an auditory mod-ality but not as well as with a visual or tactilemodality. Using an auditory modality, sightedindividuals performed more poorly than did blindsubjects, since they were not used to dealing withspatial imagery based on sound. By contrast,audition provides critical information to the blindabout their environment. Based on past research,this study used span-length tasks in which subjectstook about two seconds to articulate [2,3].Researchers have found that verbal short-termmemory decays within 2 s [16]. In our study,each number and sound was spoken for 3 s inexperiments 1 and 2. Even though blind individualsmay have a better auditory memory span thansighted ones, they still cannot keep an auditory
memory span for more than 10 s. This explains whythe subject’s performance dramatically degradedwhen the set size was increased. The results alsocoincided with Vanlierde and Wanet-Defalque’sreport [20].
Visual history may be a factor influencingthe subject’s performance. This study showed asignificant difference in a subject’s performancebetween congenitally and late-blind individuals.Research has reported the superiority of the lateblind in constructing mental representations withan auditory modality. This pattern of results issimilar to that of Hollins’ [9] research. Becausecongenitally blind individuals lack visual experi-ences, it is difficult for them to construct theconcept of a plane map. The congenitally blindcompensate for the lack of visual input bydeveloping more acute auditory perceptions [14].In our research, blind individuals seemed todevelop their mental representation with auditoryand tactile modality. The late-blind subjects havevisual experience and may handle mental imageryby relying on their past visual experience withan auditory modality. Results showed no differencebetween an auditory modality and a tactilemodality for the late blind. On the other hand,the congenitally blind, never having had visualexperience, constructed mental imagery more easilyby a tactile modality than by an auditory modality.
The results of this study provide good evidencethat blind individuals develop cross-modal com-pensation after sensory deprivation. That is, blindindividuals can construct spatial informationas well as sighted individuals. The late blind usedtheir previous visual experience and auditorymodality to perform the tasks in this study.Duration of blindness rather than age may deter-mine spatial memory performance for the lateblind. Future studies could provide additionalevidence. The results of this study have potentialimplications at the evidence level. Designingmulti-sensory appliances for supporting navigationand mobility for blind individuals will be crucial.
Notes on contributors
Min-Sheng Chen is an Associate Professor in theDepartment of Industrial Engineering andManagement, National Yunlin University of Scienceand Technology, Taiwan. She received her MS degree inIndustrial Engineering from Texas Tech University,USA, in 1992, and her PhD degree in Psychology atNational Chung Cheng University, Taiwan, in 2004.Her research interests include human information pro-cessing, memory in aging, human computer interfaces,and applications of cognitive psychology.
Ching-Kai Huang is a graduate student in theDepartment of Industrial Engineering and Managementat National Yunlin University of Science and
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Technology, Taiwan, Republic of China. He received hisMasters degree in 2007.
Chih-Nan Wang is a PhD student in the Departmentof Industrial Engineering and Management at NationalYunlin University of Science and Technology, Taiwan,Republic of China.
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