studies have shown working memory [ 13 ] and attention [ 4 , 5 ] deficits in individuals with schizophrenia . working memory is a temporary storage facility that lasts for only seconds , accessible to conscious attention . the visuospatial sketchpad theory proposes that the visual and spatial impression of a limited number of objects is temporarily stored , manipulated , and allows subselections to be created through the focus of attention . attention is the cognitive process of selecting some elements , from an environment ( real or otherwise ) while ignoring other elements and it is a precondition for exercising working memory . it determines what enters into working memory , and shifting attention can disrupt the contents of working memory . when presented with a shorter stimulus , the stimuli 's entrance into working memory may be less complete . currently , tests for working memory include the n - back task   which is a continuous performance task commonly used to measure a part of working memory , the sternberg item recognition paradigm [ 11 , 12 ] , the visual patterns test , the spatial working memory task ( spwm ) , and others [ 1518 ] . existing tests for attention include the continuous performance test ( cpt ) [ 19 , 20 ] and the sustained attention test . some existing tests require extended periods of time to complete or require verbal knowledge , which may impede the subject 's ability to complete the test due to age or education . with the objective of creating a simple test of working memory and attention for use in treatment of neuropsychiatric disorders , we developed a spatial working memory and attention test on paired symbols ( swaps ) . they were divided into 5 groups by age : a 10s age group ranging from 12 to 16 years old ( 14.2  0.1 , n = 43 ( male = 23 , female = 20 ) ) ; 20s age group ranging from 20 to 27 years old ( 23.8  0.2 , n = 37 ( male = 18 , female = 19 ) ) ; 30s age group ranging from 30 to 39 years old ( 33.7  0.5 , n = 41 ( male = 21 , female = 20 ) ) ; 40s age group ranging from 40 to 49 years old , ( 45.5  0.5 , n = 35 ( male = 17 , female = 18 ) ) ; 50s age group ranging from 50 to 60 years old ( 53.5  0.5 , n = 32 ( male = 17 , female = 15 ) ) . all schizophrenia patients were recruited from shanghai mental health center and wuxi mental health center . they had been diagnosed with schizophrenia according to the criteria set forth by the dsm - iv - tr publication , with the following exclusion criteria : alcohol or drug abuse or dependence , major medical or neurological illness , or noticeable lower intelligence as determined by at least two professional psychiatrists . a total of 72 schizophrenia patients currently undergoing treatment in these hospitals , ages 13 to 40 , were divided into 3 groups according to age : a sz10s group ranging from 13 to 19 years old ( 15.8  0.2 , n = 24 ( male = 11 , female = 13 ) ) ; sz20s group ranging from 20 to 29 years old ( 25.0  0.5 , n = 24 ( male = 12 , female = 12 ) ) ; sz30s group ranging from 30 to 40 years old ( 35.9  0.6 , n = 24 ( male = 12 , female = 12 ) ) . all subjects participated with their own free will and with informed consent . the study was approved by the bio - ethics board of the bio - x institutes , shanghai jiao tong university . the novel spatial working memory and attention test on paired symbols ( swaps ) was inspired by the chinese historical jiugongtu ( see supplementary figure 3 in supplemetary materials available online at http://dx.doi.org/10.1155/2013/130642 ) [ 22 , 23 ] . jiugongtu is well known in chinese culture , making it a familiar spatial map for subjects . the swaps test uses the nine spaced jiugongtu grid as a background but filled with paired symbols . the test is composed of a visual two - dimensional grid plane presented to the subjects on a computer screen ( figure 1 ) . the grid is segmented into nine regular squares , each of which might contain a symbol . the subjects have been instructed to use a pointing device to select the grid location of the matching and missing symbol on the screen . the test randomly presents symbol pairs in different locations on the grid , for a learning time duration ( lt ) of 0.5 seconds or 2 seconds ( figure 1(a ) ) . the test then presents an empty screen for a duration of time which we call the delay span ( d ) , which is 0.5 seconds or 2 seconds ( figure 1(b ) ) , and then randomly presents only one of the symbols . the participants are expected to select the location of the missing one of the paired symbols ( figure 1(c ) ) or an  uncertain  button beside the grid . as the learning time lt and delay span d can be 0.5 seconds or 2 seconds , this allows for 4 possible combinations . we record the reaction time of the participants beginning from when the symbol is presented during the memory recall phase ( figure 1(c ) ) and ending when the subject makes a choice with the pointing device . the percentage of correct choices ( c ) divided by reaction time ( r ) produces a score , calculated as the efficiency score ( c / r ) . we also show the percentage of correct choices and reaction time results separately in supplementary figures 48 and supplementary tables 35 . there are 4 levels of difficulty , which we call loads ( 1 to 4 ) , where the load is the quantity of paired symbols presented on one grid . load one has a single pair of symbols , load two has 2 symbol pairs , load three has 3 and load four has 4 ( figures 1(e)1(h ) ) . the swaps test consists of 101 trials with the test lasting 7 minutes on average . the first 5 trials are all load one difficulty and are not used in the result . they exist to provide a short practice exercise for the subject prior to the administration of the real test . the next 96 trials are randomly arranged , consisting of 32 trials of all combinations of lt ( 0.5 seconds or 2 seconds ) and d ( 0.5 seconds and 2 seconds ) per load , for difficulty loads two through four . anova analyses and fisher 's plsd   were used for statistical comparisons between groups as described in the results section or in figure legends . the control group was composed of 188 healthy volunteers from 12 to 60 years old . age may be a factor influencing both accuracy and reaction time in completing swaps [ 25 , 26 ] , so participants were divided into groups by age as 10s , 20s , 30s , 40s ,   and 50s . compared to the 10s age group , the 20s group showed significantly better performance in almost all combinations of load level , learning time and delay span ( figure 2 , supplementary table 1 ) . swaps showed the development of spatial working memory and attention reached a peak in the 20s group and then declined with increasing age . with a shorter learning time of 0.5 seconds which requires closer attention , the result showed significantly better performance in the 20s age group ( figures 2(a ) and 2(b ) ) . seventy - two schizophrenia patients 13 to 40 years old were divided into 3 groups according to age : sz10s , sz20s and sz30s . interestingly , schizophrenia patients failed to display maturation of spatial working memory and attention capacity in ages 2029 compared to ages 1319 ( figures 2(e)2(h ) , supplementary table 1 ) . compared to the 20s control group the sz30s group in schizophrenia patients also showed significant deficits in test scores under all combinations compared to the 30s control group ( supplementary figure 2 ) . however , sz10s schizophrenia patients did not show a difference ( under all test conditions ) compared to the 10s control group ( supplementary figure 1 ) . detailed comparative results of schizophrenia and control groups are shown in supplementary tables 1 and 2 . difficulty loads of symbols , stimulus duration ( learning time ) , and delay span are important for measuring working memory and attention . in order to guide the development of swaps , we conducted a preliminary study in 31 healthy subjects with ages ranging from 18 to 24 years old . the preliminary study had random learning times ( 05 seconds ) and delay spans ( 05 seconds ) ( supplementary figure 9 ) . the first versions of the test needed to determine the most appropriate lt and d to show differentiation between loads and we use correct responses to analyze because it is more sensitive within age groups . supplementary figure 9(a ) shows the variation of correct responses through difficulty loads two , three and four , presenting evidence that the design of the test can discriminate between difficulty loads . we found that d of up to 2 seconds had the same results as d of up to 5 seconds ( supplementary figure 9(b ) ) . the added time did not increase accuracy in responses , and so we shortened d in our test design to 2 seconds . we found that lt shows the largest differences between loads when lt has a value of between 0 and 2 seconds , and when lt exceeds 2 seconds the test results for all loads of difficulty begin to converge toward a higher percentage of correct response ( supplementary figure 9(c ) ) . learning times of 02 seconds and delay spans below 2 seconds showed good results and could shorten the testing time . we use values of 0.5 seconds and 2 seconds [ 27 , 28 ] for both learning time and delay span . in the swaps test , observers focus their attention on the locations ( spatial locations ) and features ( different symbols ) . a longer delay d of 2 seconds requires better working memory , in the most challenging condition of lt = 0.5 seconds , d = 2 seconds and load 4 , the healthy control showed the lowest score , and 20  s control group showed peak score compared to other age groups . in contrast , the sz20s schizophrenia group did not show the peak score when compared to the sz10s and sz30s groups . both accuracy and reaction time are important variables which reflect the memory and attention capacity of subjects who take the swaps test . we used an efficiency score ( percentage of correct choice divided by average reaction time )   to display a simple result for working memory and attention . the schizophrenia group sz20s showed more deficits in accuracy than reaction time compared to the 20s twenties age range control group ( supplementary figure 7 ) , and the sz30s schizophrenia group showed greater deficits in reaction time than accuracy compared to the 30s thirties age range control group in thirties ( supplementary figure 8) . using the efficiency score , results revealed clearer deficits in schizophrenia patients compared to their counterparts in the twenties and thirties age range . in other studies an inverse efficiency score is sometimes used ; however , because in some circumstances the q score result of the swaps test can be 0 , we use an efficiency score to quantify results . cognitive abilities rise steeply from infancy to young adulthood and then are either maintained or decline to old age . brain activity studies have shown that healthy young adults develop better neurocognitive ability including working memory and attention [ 32 , 33 ] . the swaps test has shown a plausible developmental pattern in healthy controls especially in difficulty load three and four , which developed well in the 20s group from the 10s group and then decline with increasing age . the more interesting finding in this study is that schizophrenia patients showed no working memory and attention improvement with age when comparing sz10s to sz20s . is it because the developmental process of people with schizophrenia is halted that the spatial working memory and attention of the patients becomes worse in their twenties ? to discover the answer to this , we may need to test more finely subdivided age groups both in control and in schizophrenia patients . more importantly , we may need to do a longitudinal study of swap tests from childhood to early adulthood for patients [ 34 , 35 ] . a limitation of this study is that the schizophrenic group was comprised of patients who were diagnosed as schizophrenic and currently undergoing various treatments for schizophrenia . these treatments might influence the performance of spatial working memory and attention in patients . besides , the age of onset , the course of disease , and education of participants maybe the influence factors , and we made a table ( supplementary table 6 ) to show these detailed information . we must treat the conclusion with caution as we can not exclude the effect of treatment in the current study . because of these limitations , it is worth testing first - episode schizophrenia patients to confirm swaps test results in future studies . gender was not a dominant factor affecting the score of swaps test ( supplementary table 7 ) . the test is simple , automatic , and results can be interpreted at the end of the test . it does not burden the test participant more than requiring a few minutes of time looking at a computer screen . swaps was developed with the goal of creating a simple test of working memory and attention for use in clinical studies in china . however , it can be easily adapted by people worldwide as it uses simple symbols . the symbols and duration time also can be easily modified by the investigator for the purposes of their own studies . this short test of attention and spatial working memory may be a useful tool in studying other mental illness such as attention deficit hyperactivity disorder , major depressive disorders , and bipolar disorder . it may also be used as an objective indicator in determining effects of treatment for neuropsychiatric disorders . moreover , swaps can be combined with fmri , pet , or eeg methodologies in future studies . as the test is computer - based , it can easily be integrated into many situations and resulting data can be analyzed automatically . swaps showed developmental maturation of spatial working memory and attention in ages 2027 which then declined with increasing age . schizophrenia patients failed to display a developmental peak of those cognitive abilities in ages 2029 and had significant deficits compared to control groups in adults . our data suggests that this simple swaps test can be a useful tool for studies of spatial working memory and attention in neuropsychiatric disorders .
people with neuropsychiatric disorders such as schizophrenia often display deficits in spatial working memory and attention . evaluating working memory and attention in schizophrenia patients 
 is usually based on traditional tasks and the interviewer 's judgment . 
 we developed a simple spatial working memory and attention test on paired symbols ( swaps ) . 
 it takes only several minutes to complete , comprising 101 trials for each subject . in this study , we tested 72 schizophrenia patients and 188 healthy volunteers in china . in a healthy control group with ages ranging from 12 
 to 60 , the efficiency score ( accuracy divided by reaction time ) reached a peak in the 2027 age range and then declined with increasing age . 
 importantly , schizophrenia patients failed to display this developmental trend in the same age range and adults had significant deficits compared to the control group . 
 our data suggests that this simple spatial working memory and attention test on paired symbols can be a useful tool for studies of spatial working memory and attention in neuropsychiatric disorders .