the intermediate stage between cognitive health and dementia   has been defined as mild cognitive impairment ( mci ) and has been widely described in epidemiological and clinical studies . criteria for mci require the report of memory problems or other cognitive function , objective cognitive impairment ( a test score of 1.5 standard deviation below the age - adjusted mean values ) , absence of dementia and intact daily functioning . subjects with mci seem to be at higher risk for conversion to dementia , particularly alzheimer 's disease . traditionally , the cognitive evaluation of patients relies on neuropsychological tests . identifying executive function deficits allows us to detect subjects with mci . among the deficits , we observe the presence of alterations of working memory and visuospatial sketchpad the visuospatial sketchpad includes a visual component and a spatial component . from the neuropsychological approach , a battery of tests is available that specifically explores visual perception abilities ( e.g. , the rey - osterrieth test , raven 's progressive matrices , the trail making test part a , and the clock - drawing test ) and visuospatial memory [ e.g. , the corsi block - tapping test ( cbt ) , memory tests with simple or complex environments ] . in 2007 , alescio - lautier et al .   observed that the deficits in visuospatial short - term memory are stronger and appear earlier than the deficits related to short - term visual memory in patients with mci or alzheimer 's disease compared to healthy elderly subjects . it is acknowledged that visuospatial working memory can be explored using the cbt test , which involves the encoding of visual stimuli , the short - term storage of spatial location , the sequence order , and the maintenance of information over time . age has a significant impact on the completion of this test ( i.e. , advanced age is associated with lower performance ) ; regardless of the severity of their disease , the patients with mild and moderate alzheimer 's disease perform worse than the healthy subjects of similar age . despite a significant link between the decrease in the performance on the corsi test and the development of cognitive problems , few investigations have been conducted in subjects with mci , and the results are varied . moreover , it has been suggested that a decrease in visuospatial ability could be a more sensitive indicator of cognitive decline   than noticeable deficits in language or speech problems . several recent studies have simultaneously attempted to explore visuospatial working memory in the navigation context using an adaptation of the cbt , i.e. , the walking corsi test ( walct ) . the walct , which is a recently developed psychometric tool , evaluates the memory storage of a sequence of places in a defined area . this spatial navigation task has been studied in healthy older subjects , neglect patients , patients with epilepsy   and brain - injured patients . the studies have shown that these types of patients perform worse on the walct test than the healthy controls , but no study has been proposed to evaluate the performance of subjects with mci . however , several studies that have investigated performance on spatial navigation tasks have shown that , compared to the healthy subjects , the patients with alzheimer 's disease performed worse in routine recognition tasks   or an adaptation of the morris water maze task . the patients with alzheimer 's disease demonstrated a spatial disorientation that is characterised by difficulties in recognising scenery , a path or a road in a real or virtual environment . the loss of visuospatial memory appears early at a stage of mci and can be observed in navigation tests . in patients with dementia , the processes involved in wayfinding in a navigation task are similar to those involved in problem - solving tasks . moving in a complex environment requires several spatio - cognitive stages , such as searching and treating relevant information and organising information in a hierarchical way to accomplish a goal . therefore , problem - solving processes may be involved during cbt , although the planning stage is absent . in this particular cbt task , when one seeks an answer ( the solution ) , one can tackle the problem in various manners ( changes in viewpoints , training and memorising strategies ) . therefore , the answers can be analysed by evaluating the strategies used . for the present , the only available method for analysing performance in cbt is the span score . no studies thus far have used a strategy analysis to investigate performance on the cbt or on the walct . in this context , such an approach could be of interest for assessing subjects with mci . first , we aimed to determine whether the assessment of visuospatial working memory in the corsi test and complex navigation task is a good indicator of cognitive impairment in the early stages of a dementing illness . second , we analysed the different strategies used by subjects in different tests and investigated whether these cognitive strategies were related to cognitive decline . we used a newly designed version of the walct , employing the  magic carpet . we hypothesised that the analysis of the strategies used by the patients in the different corsi tests will reveal additional information than the corsi span score in subjects with mci . the present cross - sectional study included 51 subjects , 15 of whom were young subjects ( mean , 25.1 years ; 12 women , 3 men ) , 21 healthy older subjects ( mean , 73.8 years ; 16 women , 5 men ) and 15 subjects with mci ( mean , 76.6 years ; 12 women , 3 men ) . all subjects lived in a community dwelling , had not complained about the quality of their gait or balance and were able to walk without assistance . the exclusion criteria included the following : any objective gait disorder due to parkinson 's disease , previous stroke , clinical osteoarthritis in the lower limb joints , myopathy , or neuropathy verified by a formal clinical examination , the presence of depressive symptoms or taking medication . we recruited 15 young subjects , the majority of whom were university students , and 21 healthy older participants from noninstitutionalised volunteers aged over 65 years . the elderly healthy controls were free of significant cognitive complaints ; however , they were similar to the mci group in age and gender . all participants in the control group were recruited through mail notifications and other types of announcements . most of the participants with mci were recruited from a memory centre in paris , france . the participants were diagnosed with mci according to the petersen 2004 criteria , which included the presence of subjective memory complaints from the patient and family , objective cognitive impairment , preserved general intellectual function , absence of significant functional impairment , and absence of clinical dementia . the mci sample was divided into three groups : amnestic single domain ( amci ; only memory deficit , n = 6 ) , nonamnestic single domain ( namci ; language , executive function , visuospatial relations , n = 3 ) , and amnestic multiple domain ( ammci ; combination of memory deficit and executive dysfunctions , n = 6 ) . all subjects underwent a clinical and a neuropsychological evaluation , which was conducted by a trained team . all volunteers underwent a battery of rapid cognitive impairment tests that were administered by a neuropsychologist and that included the mini - mental state examination , the frontal assessment battery , the trail making test , part a and part b , the stroop test , the wechsler adult intelligence scale   and the dubois ' 5-word test . mood and depression finally , the participants were asked to perform spontaneous walking for 10 m in a standardised environment on an 8-meter electronic walkway ( gaitrite ; cir systems , inc . , the test involves nine wooden blocks ( 3  3 cm ) that are randomly distributed on a board with a dimension of 25  30 cm . first described by milner   and developed by corsi , this test requires the patient to press on a series of blocks . first , the action sequence is shown to the patient ; subsequently , the patient must recall the sequence and immediately repeat it in the same order . both the traditional and computerised versions of this test provide similar outcomes . in this test , the examiner first presents a short series ( i.e. , starting with a 2-block sequence ) and gradually increases the length of the sequence if the patient 's response is correct . in the present study , we used a modified cbt ( mcbt ) that was developed by the collge de france , paris ( an electronic version is available ) ( fig . 1 ) . the mcbt uses the same protocol developed by milner in 1971 ; however , the board and cubes are plastic , and the sequences are shown on a computer . the blocks are illuminated every 1,500 ms , and the end of the sequence is marked by a tone , at which time the subject is asked to reproduce the sequence . after the first three simple sequences have been presented , if at least two of them have been reproduced correctly , the next level is administered ( i.e. , a 3-block sequence ) . when two trials out of three at the same level have not been correctly reproduced , the test stops . the score , which is the length of the last sequence correctly reproduced , is recorded . the experimental conditions were similar to those described by piccardi et al .   on the classical walking corsi , except that we used an electronic version . magic carpet , which is a set of tiles that are lit by a computer allowing a large variety of possible combinations of sequences . this experimental set - up was developed at the collge de france   ( fig . the modified walking corsi test ( mwct ) was performed in an empty room with a dimension of 4  5 m ; the walls were covered with curtains that served to hide external references ( e.g. , doors and windows ) . the magic carpet is composed of nine white panels ( 30  30 cm ) that are placed on a grey carpet with a dimension of 250  300 cm , using a layout similar to the cbt on a larger scale ( scale 10:1 ) . each panel is equipped with force sensors , and the panels are connected to a computer workstation to record the subject 's responses . to repeat the sequence , this process was filmed to study the movement strategies used by the subjects as they walked and navigated in the environment . in the mwct , the experimental conditions ( e.g. , instructions and scoring ) were the same as those in the mcbt , including the starting position . in the test proposed by piccardi et al . , the patient and the examiner had the same starting point in the walct , which is not the case in the cbt . the order of the successive tests ( i.e. , mcbt and mwct ) was counterbalanced among the subjects in each group . although the span score is the same as the score obtained in the cbt test , we have identified ways to obtain additional information . simple problem - solving activity because the subject must remember a sequence of movements by storing the illuminated blocks one by one and then reconstituting the sequence . simple because it does not require the planning stages of a complex problem - solving activity ( e.g. , the tower of hanoi ) . in this context , the model published by richard et al .   could be an elegant way to analyse the sequences of movements performed by the subject . the basic idea is that an individual will try to find the best compromise to solve a problem under a set of constraints . the subject will try to respect all constraints , but in certain cases called  deadlocks , he will decide not to consider one constraint . usually , he decides not to follow the constraint that he considers to be less important or the one that is the most restrictive . the different steps involved in successful information processing in the test require the adequate storage and recall of the parameters of locomotor trajectories ( i.e. , choosing the correct direction , the precise localisation of the blocks and the correct number of blocks ) . if these three criteria are correctly met , the visuospatial pathway is successfully reproduced by the motor or the locomotor trajectory . the analysis of different categories of trajectory errors was based on the trajectories performed by the subjects when they failed twice in one trial level . the errors were noted and described to determine the constraints that were not respected by the subjects . we have identified five strategies ( with different types of errors ) : ( s1 ) localisation(one wrong block is shown ) ; ( s2 ) inversion(two blocks are shown in the wrong order ) ; ( s3 ) approximation(sequences with several errors but with a general configuration similar to the shown sequence ) ; ( s4 ) random sequence(sequences presented without any logic ) , and ( s5 ) incomplete sequence(sequences with too many or not enough blocks ) ( fig . 2 ) . presumably , the errors in the responses of the subjects suggest that they eliminate some constraints ( e.g. , localisation , direction , or number of blocks ) . if the constraints are too strong , the subjects begin to neglect the precise localisation of each block and adopt a less suitable strategy , which makes their response approximate . finally , a lack of strategy forces the subjects to abandon all constraints ( random response ) or to show an incorrect number of blocks ( fig . this method of analysis can be presented as a graduated scale that ranges from the lack of a strategy to the most appropriate strategies . the span scores were analysed using a factorial anova ( 3  2 ) with three groups ( young subjects , healthy elderly and mci subjects ) and two conditions ( mcbt and mwct ) . the differences in cognitive performance and gait were analysed using a one - way anova . correlations between functional capacity ( walking speed ) and performance on the mcbt and mwct tests were evaluated using the spearman test . finally , the strategies were studied in two stages . first , we used a binary code ( 0 or 1 ) to show whether one strategy had been employed ( 1 ) or not ( 0 ) . subsequently , we compared the two groups of subjects ( healthy elderly subjects vs. mci patients ) for each test ( mcbt and mwct ) using the mann - whitney test . the present cross - sectional study included 51 subjects , 15 of whom were young subjects ( mean , 25.1 years ; 12 women , 3 men ) , 21 healthy older subjects ( mean , 73.8 years ; 16 women , 5 men ) and 15 subjects with mci ( mean , 76.6 years ; 12 women , 3 men ) . all subjects lived in a community dwelling , had not complained about the quality of their gait or balance and were able to walk without assistance . the exclusion criteria included the following : any objective gait disorder due to parkinson 's disease , previous stroke , clinical osteoarthritis in the lower limb joints , myopathy , or neuropathy verified by a formal clinical examination , the presence of depressive symptoms or taking medication . we recruited 15 young subjects , the majority of whom were university students , and 21 healthy older participants from noninstitutionalised volunteers aged over 65 years . the elderly healthy controls were free of significant cognitive complaints ; however , they were similar to the mci group in age and gender . all participants in the control group were recruited through mail notifications and other types of announcements . most of the participants with mci were recruited from a memory centre in paris , france . the participants were diagnosed with mci according to the petersen 2004 criteria , which included the presence of subjective memory complaints from the patient and family , objective cognitive impairment , preserved general intellectual function , absence of significant functional impairment , and absence of clinical dementia . the mci sample was divided into three groups : amnestic single domain ( amci ; only memory deficit , n = 6 ) , nonamnestic single domain ( namci ; language , executive function , visuospatial relations , n = 3 ) , and amnestic multiple domain ( ammci ; combination of memory deficit and executive dysfunctions , n = 6 ) . all subjects underwent a clinical and a neuropsychological evaluation , which was conducted by a trained team . all volunteers underwent a battery of rapid cognitive impairment tests that were administered by a neuropsychologist and that included the mini - mental state examination , the frontal assessment battery , the trail making test , part a and part b , the stroop test , the wechsler adult intelligence scale   and the dubois ' 5-word test . finally , the participants were asked to perform spontaneous walking for 10 m in a standardised environment on an 8-meter electronic walkway ( gaitrite ; cir systems , inc . , the test involves nine wooden blocks ( 3  3 cm ) that are randomly distributed on a board with a dimension of 25  30 cm . first described by milner   and developed by corsi , this test requires the patient to press on a series of blocks . first , the action sequence is shown to the patient ; subsequently , the patient must recall the sequence and immediately repeat it in the same order . both the traditional and computerised versions of this test provide similar outcomes . in this test , the examiner first presents a short series ( i.e. , starting with a 2-block sequence ) and gradually increases the length of the sequence if the patient 's response is correct . in the present study , we used a modified cbt ( mcbt ) that was developed by the collge de france , paris ( an electronic version is available ) ( fig . 1 ) . the mcbt uses the same protocol developed by milner in 1971 ; however , the board and cubes are plastic , and the sequences are shown on a computer . the blocks are illuminated every 1,500 ms , and the end of the sequence is marked by a tone , at which time the subject is asked to reproduce the sequence . after the first three simple sequences have been presented , if at least two of them have been reproduced correctly , the next level is administered ( i.e. , a 3-block sequence ) . when two trials out of three at the same level have not been correctly reproduced , the test stops . the score , which is the length of the last sequence correctly reproduced , is recorded . the experimental conditions were similar to those described by piccardi et al .   on the classical walking corsi , except that we used an electronic version . magic carpet , which is a set of tiles that are lit by a computer allowing a large variety of possible combinations of sequences . this experimental set - up was developed at the collge de france   ( fig . the modified walking corsi test ( mwct ) was performed in an empty room with a dimension of 4  5 m ; the walls were covered with curtains that served to hide external references ( e.g. , doors and windows ) . the magic carpet is composed of nine white panels ( 30  30 cm ) that are placed on a grey carpet with a dimension of 250  300 cm , using a layout similar to the cbt on a larger scale ( scale 10:1 ) . each panel is equipped with force sensors , and the panels are connected to a computer workstation to record the subject 's responses . to repeat the sequence , this process was filmed to study the movement strategies used by the subjects as they walked and navigated in the environment . in the mwct , the experimental conditions ( e.g. , instructions and scoring ) were the same as those in the mcbt , including the starting position . in the test proposed by piccardi et al . , the patient and the examiner had the same starting point in the walct , which is not the case in the cbt . the order of the successive tests ( i.e. , mcbt and mwct ) was counterbalanced among the subjects in each group . although the span score is the same as the score obtained in the cbt test , we have identified ways to obtain additional information . simple problem - solving activity because the subject must remember a sequence of movements by storing the illuminated blocks one by one and then reconstituting the sequence . simple because it does not require the planning stages of a complex problem - solving activity ( e.g. , the tower of hanoi ) . in this context , the model published by richard et al .   could be an elegant way to analyse the sequences of movements performed by the subject . the basic idea is that an individual will try to find the best compromise to solve a problem under a set of constraints . the subject will try to respect all constraints , but in certain cases called  deadlocks , he will decide not to consider one constraint . usually , he decides not to follow the constraint that he considers to be less important or the one that is the most restrictive . the different steps involved in successful information processing in the test require the adequate storage and recall of the parameters of locomotor trajectories ( i.e. , choosing the correct direction , the precise localisation of the blocks and the correct number of blocks ) . if these three criteria are correctly met , the visuospatial pathway is successfully reproduced by the motor or the locomotor trajectory . the analysis of different categories of trajectory errors was based on the trajectories performed by the subjects when they failed twice in one trial level . the errors were noted and described to determine the constraints that were not respected by the subjects . we have identified five strategies ( with different types of errors ) : ( s1 ) localisation(one wrong block is shown ) ; ( s2 ) inversion(two blocks are shown in the wrong order ) ; ( s3 ) approximation(sequences with several errors but with a general configuration similar to the shown sequence ) ; ( s4 ) random sequence(sequences presented without any logic ) , and ( s5 ) incomplete sequence(sequences with too many or not enough blocks ) ( fig . 2 ) . presumably , the errors in the responses of the subjects suggest that they eliminate some constraints ( e.g. , localisation , direction , or number of blocks ) . if the constraints are too strong , the subjects begin to neglect the precise localisation of each block and adopt a less suitable strategy , which makes their response approximate . finally , a lack of strategy forces the subjects to abandon all constraints ( random response ) or to show an incorrect number of blocks ( fig . this method of analysis can be presented as a graduated scale that ranges from the lack of a strategy to the most appropriate strategies . the test involves nine wooden blocks ( 3  3 cm ) that are randomly distributed on a board with a dimension of 25  30 cm . first described by milner   and developed by corsi , this test requires the patient to press on a series of blocks . first , the action sequence is shown to the patient ; subsequently , the patient must recall the sequence and immediately repeat it in the same order . both the traditional and computerised versions of this test provide similar outcomes . in this test , the examiner first presents a short series ( i.e. , starting with a 2-block sequence ) and gradually increases the length of the sequence if the patient 's response is correct . in the present study , we used a modified cbt ( mcbt ) that was developed by the collge de france , paris ( an electronic version is available ) ( fig . 1 ) . the mcbt uses the same protocol developed by milner in 1971 ; however , the board and cubes are plastic , and the sequences are shown on a computer . the blocks are illuminated every 1,500 ms , and the end of the sequence is marked by a tone , at which time the subject is asked to reproduce the sequence . after the first three simple sequences have been presented , if at least two of them have been reproduced correctly , the next level is administered ( i.e. , a 3-block sequence ) . when two trials out of three at the same level have not been correctly reproduced , the test stops . the score , which is the length of the last sequence correctly reproduced , is recorded . in the present study , the experimental conditions were similar to those described by piccardi et al .   on the classical walking corsi , except that we used an electronic version . magic carpet , which is a set of tiles that are lit by a computer allowing a large variety of possible combinations of sequences . this experimental set - up was developed at the collge de france   ( fig . the modified walking corsi test ( mwct ) was performed in an empty room with a dimension of 4  5 m ; the walls were covered with curtains that served to hide external references ( e.g. , doors and windows ) . the magic carpet is composed of nine white panels ( 30  30 cm ) that are placed on a grey carpet with a dimension of 250  300 cm , using a layout similar to the cbt on a larger scale ( scale 10:1 ) . each panel is equipped with force sensors , and the panels are connected to a computer workstation to record the subject 's responses . to repeat the sequence , this process was filmed to study the movement strategies used by the subjects as they walked and navigated in the environment . in the mwct , the experimental conditions ( e.g. , instructions and scoring ) were the same as those in the mcbt , including the starting position . in the test proposed by piccardi et al . , the patient and the examiner had the same starting point in the walct , which is not the case in the cbt . the order of the successive tests ( i.e. , mcbt and mwct ) was counterbalanced among the subjects in each group . although the span score is the same as the score obtained in the cbt test , we have identified ways to obtain additional information . simple problem - solving activity because the subject must remember a sequence of movements by storing the illuminated blocks one by one and then reconstituting the sequence . simple because it does not require the planning stages of a complex problem - solving activity ( e.g. , the tower of hanoi ) . in this context , the model published by richard et al .   could be an elegant way to analyse the sequences of movements performed by the subject . the basic idea is that an individual will try to find the best compromise to solve a problem under a set of constraints . the subject will try to respect all constraints , but in certain cases called  deadlocks , he will decide not to consider one constraint . usually , he decides not to follow the constraint that he considers to be less important or the one that is the most restrictive . the different steps involved in successful information processing in the test require the adequate storage and recall of the parameters of locomotor trajectories ( i.e. , choosing the correct direction , the precise localisation of the blocks and the correct number of blocks ) . if these three criteria are correctly met , the visuospatial pathway is successfully reproduced by the motor or the locomotor trajectory . the analysis of different categories of trajectory errors was based on the trajectories performed by the subjects when they failed twice in one trial level . the errors were noted and described to determine the constraints that were not respected by the subjects . we have identified five strategies ( with different types of errors ) : ( s1 ) localisation(one wrong block is shown ) ; ( s2 ) inversion(two blocks are shown in the wrong order ) ; ( s3 ) approximation(sequences with several errors but with a general configuration similar to the shown sequence ) ; ( s4 ) random sequence(sequences presented without any logic ) , and ( s5 ) incomplete sequence(sequences with too many or not enough blocks ) ( fig . 2 ) . presumably , the errors in the responses of the subjects suggest that they eliminate some constraints ( e.g. , localisation , direction , or number of blocks ) . if the constraints are too strong , the subjects begin to neglect the precise localisation of each block and adopt a less suitable strategy , which makes their response approximate . finally , a lack of strategy forces the subjects to abandon all constraints ( random response ) or to show an incorrect number of blocks ( fig . this method of analysis can be presented as a graduated scale that ranges from the lack of a strategy to the most appropriate strategies . the span scores were analysed using a factorial anova ( 3  2 ) with three groups ( young subjects , healthy elderly and mci subjects ) and two conditions ( mcbt and mwct ) . the differences in cognitive performance and gait were analysed using a one - way anova . correlations between functional capacity ( walking speed ) and performance on the mcbt and mwct tests were evaluated using the spearman test . finally , the strategies were studied in two stages . first , we used a binary code ( 0 or 1 ) to show whether one strategy had been employed ( 1 ) or not ( 0 ) . subsequently , we compared the two groups of subjects ( healthy elderly subjects vs. mci patients ) for each test ( mcbt and mwct ) using the mann - whitney test . the statistical analyses were performed using the statistica version 9 ( statsoft inc . , tulsa , okla . the results of the different cognitive tests revealed a pronounced memory deficit ( dubois ' 5-word test ) , impaired global executive function ( frontal assessment battery ) , mental inhibition ( stroop test ) and especially impaired mental flexibility ( trail making test ) in subjects with mci relative to healthy elderly subjects and young subjects ( p < 0.05 for each test ) ( table 1 ) . other cognitive functions , including global cognitive efficiency ( mini - mental state examination ) , intelligence ( wechsler adult intelligence scale ) and visuoconstructive abilities , were well preserved in normal ageing and pathological states . there was also a decrease in the trail making test performance for healthy elderly subjects relative to the younger subjects ( p < 0.05 ) . finally , a significant difference ( p < 0.05 ) was found in walking speed between the healthy older adults and the young adult subjects with mci but not between the healthy elderly group and the group with mci ( table 1 ) . no differences in anthropometric variables ( i.e. , size of shoes , weight , and height ) were noticed among the different groups of subjects . there was no correlation between walking speed and performance on the mcbt ( r = 0.19 , p < 0.05 ) . however , a positive and significant correlation was revealed between the mwct performance and walking speed ( r = 0.32 , p < 0.05 ) . the visuospatial working memory was more impaired in the complex navigation task ( mwct = 4.3  0.9 ) than in the corsi test ( mcbt = 5.3  0.8 ) . the mwct showed a significant difference ( f1 , 49 = 21.7 , p < 0.001 ) , with better performance on the mcbt than on the mwct for young subjects ( mcbt = 6.2  0.6 vs. mwct = 5.3  1.0 ) , for the elderly ( mcbt = 5.0  0.7 vs. mwct = 4.0  0.7 ) and for subjects with mci ( mcbt = 4.7  0.8 vs. mwct = 4.1  0.9 ) ( fig . we also found a significant effect when we compared individual performance ( f2 , 48 = 26.4 , p < 0.001 ) . the young subjects performed better than the healthy elderly subjects and the subjects with mci both on the mcbt and mwct . however , there was no significant difference between the two groups of older subjects on the mcbt or the mwct ( similar conclusions were drawn using the anova with our three groups of subjects and using nonparametric statistics when only the two groups of elderly subjects were considered ) ( fig . , the span score analysis did not present any interaction among the groups of subjects ( f2 , 48 = 0.51 , p = 0.59 ) . problem - solving strategies were investigated because 90% of the results demonstrated a span score of 4 for the mcbt and 5 for the mwct . in the qualitative analysis , we observed different behavioural patterns in visuospatial processing between the healthy elderly subjects and the subjects with mci in the mwct ( fig . 4 ) . during spatial navigation , the behavioural profiles were specific in each group . the strategy s1 ( localisation ) was used significantly more often in the healthy elderly than in the subjects with mci ( p = 0.005 ) , and the strategy s4 ( random sequence ) was used significantly more often in the subjects with mci than in the healthy elderly subjects ( p = 0.02 ) . the patients with mci demonstrated a lack of strategies ( random sequence ) , whereas the healthy elderly subjects appeared to use the most appropriate strategies ( localisation ) . in contrast , the analysis of strategies used on the mcbt showed no difference between the two groups . the results of the different cognitive tests revealed a pronounced memory deficit ( dubois ' 5-word test ) , impaired global executive function ( frontal assessment battery ) , mental inhibition ( stroop test ) and especially impaired mental flexibility ( trail making test ) in subjects with mci relative to healthy elderly subjects and young subjects ( p < 0.05 for each test ) ( table 1 ) . other cognitive functions , including global cognitive efficiency ( mini - mental state examination ) , intelligence ( wechsler adult intelligence scale ) and visuoconstructive abilities , were well preserved in normal ageing and pathological states . there was also a decrease in the trail making test performance for healthy elderly subjects relative to the younger subjects ( p < 0.05 ) . finally , a significant difference ( p < 0.05 ) was found in walking speed between the healthy older adults and the young adult subjects with mci but not between the healthy elderly group and the group with mci ( table 1 ) . no differences in anthropometric variables ( i.e. , size of shoes , weight , and height ) were noticed among the different groups of subjects . there was no correlation between walking speed and performance on the mcbt ( r = 0.19 , p < 0.05 ) . however , a positive and significant correlation was revealed between the mwct performance and walking speed ( r = 0.32 , p < 0.05 ) . the visuospatial working memory was more impaired in the complex navigation task ( mwct = 4.3  0.9 ) than in the corsi test ( mcbt = 5.3  0.8 ) . the mwct showed a significant difference ( f1 , 49 = 21.7 , p < 0.001 ) , with better performance on the mcbt than on the mwct for young subjects ( mcbt = 6.2  0.6 vs. mwct = 5.3  1.0 ) , for the elderly ( mcbt = 5.0  0.7 vs. mwct = 4.0  0.7 ) and for subjects with mci ( mcbt = 4.7  0.8 vs. mwct = 4.1  0.9 ) ( fig . we also found a significant effect when we compared individual performance ( f2 , 48 = 26.4 , p < 0.001 ) . the young subjects performed better than the healthy elderly subjects and the subjects with mci both on the mcbt and mwct . however , there was no significant difference between the two groups of older subjects on the mcbt or the mwct ( similar conclusions were drawn using the anova with our three groups of subjects and using nonparametric statistics when only the two groups of elderly subjects were considered ) ( fig . , the span score analysis did not present any interaction among the groups of subjects ( f2 , 48 = 0.51 , p = 0.59 ) . problem - solving strategies were investigated because 90% of the results demonstrated a span score of 4 for the mcbt and 5 for the mwct . in the qualitative analysis , we observed different behavioural patterns in visuospatial processing between the healthy elderly subjects and the subjects with mci in the mwct ( fig . 4 ) . during spatial navigation , the behavioural profiles were specific in each group . the strategy s1 ( localisation ) was used significantly more often in the healthy elderly than in the subjects with mci ( p = 0.005 ) , and the strategy s4 ( random sequence ) was used significantly more often in the subjects with mci than in the healthy elderly subjects ( p = 0.02 ) . the patients with mci demonstrated a lack of strategies ( random sequence ) , whereas the healthy elderly subjects appeared to use the most appropriate strategies ( localisation ) . in contrast , the analysis of strategies used on the mcbt showed no difference between the two groups . visuospatial memory , which plays a basic role in daily life , is required for orientation and spatial localisation and for using a navigation map . in the present study , we were especially interested in the early deficits in visuospatial memory that occur in subjects with mci . we have shown a significant impact of ageing in the performances obtained in the corsi tests in traditional and navigation conditions . moreover , the strategy analysis was able to reveal differences in problem solving in subjects with mci and healthy elderly subjects , especially in the navigation task ( mwct ) . we can speculate whether the performances obtained in the two kinds of corsi tests ( traditional and navigation ) that we used are connected to similar or different memory systems . several studies have supported the idea that performance on the cbt and walct relies on different memory systems . this hypothesis is consistent with the literature ; we know that visuospatial memory is not an individualised structure . the model proposed by piccardi et al . has one spatial memory system for objects that are close to the subject ( peripersonal / reaching memory system ) and another system for spatial navigation purposes ( spatial navigation ) . in the present study , our results and the findings of recent studies in the literature suggested that there are two memory systems for processing visuospatial information : one for peripersonal / reaching memory that addresses objects that are close to the subject and another process that involves spatial navigation . however , our data are in conflict with the results obtained by piccardi et al . , which show that the span score is more important on the walct than on the cbt in young subjects . they introduced the hypothesis that the difference in the performance on these two tests was related to enriched and diversified sensory integration ( visual , vestibular , and proprioceptive ) that occurs during the navigation task and facilitates the processing of mnesic memory processes . we attribute the discrepancies in the results of these two studies to the specific methodological conditions used in our tests . our subjects were assessed similarly in the mcbt and the mwct , in contrast to the study by piccardi et al . , where the sequences were produced by the experimenter and not by a computer . thus , we assume that seeing the experimenter perform the sequence on the mat allows the patient to mentally simulate the action by activating different sensory inputs ; such processes were impossible in our mwct . additionally , we can explain the discrepancy between the results on the mwct and the mcbt by the complex navigation sequence because our subjects had to update their spatial map at each step / block of the sequence on the mwct . memorising the sequence is achieved by spatially mapping the environment from a particular point of view , whereas repetition alters the subject 's own spatial references and changes the subject 's perspective . a recent study using the magic carpet has shown the impact of perspective changes on learning a sequence by using visuospatial working memory . in the present study , we investigated the effect of healthy and pathological ageing on the performances in two kinds of corsi tests . a recent study demonstrated that performance on the cbt and the walct begins to degrade at the age of 47 years . using the span score , we were able to show an effect of ageing on spatial short - term memory based on the performance in our two tests . the decrease in performance seems to be not only connected to the navigation task difficulty but also to the decrease in the working memory capacity because of ageing . several studies have shown a performance decrease in patients in the early - to - moderate stages of dementia compared to healthy subjects of similar age . we expected to find impaired performance in the group with mci , since the deterioration of the prefrontal cortex over time   results in cognitive difficulty in completing complex tasks that require executive functions , such as those tasks in the cbt . nevertheless , we were unable to detect any differences in performance between the healthy elderly subjects and the patients with mci in the performance of mcbt . with the additional cognitive deficits present in older subjects with mci , we considered that we would detect marked performance difficulty in subjects with mci relative to healthy elderly subjects , especially on the spatial navigation task ( i.e. , on the mwct ) . disorders of spatial orientation ( topographical disorientation ) and spatial memory deficits have been shown to represent an early sign of degenerative dementia . our data showed that the two groups of elderly subjects did not differ in their performance on the mwct , which suggests that visuospatial navigation working memory was not affected in the stage of mci . however , the subjects with dementia disorders present an important topographical orientation impairment , i.e. , an impairment in the allocentric and egocentric systems during spatial navigation   that affects their ability to create and use a spatial map . the navigation deficits observed in these patients are likely related to the brain damage that occurs in the early stages of alzheimer 's disease . additionally , many studies have highlighted changes in egocentric and allocentric navigation performed by patients with mci relative to healthy elderly subjects . one explanation for our results could be provided by the heterogeneity of our group of patients ( 6 amci , 3 namci , 6 ammci ) , which would increase the variability in the responses and therefore mask problems in the working memory . .   showed that patients with amci have a deficit in encoding and consolidating memories that are associated with hippocampal damage . the performance of subjects with amci is similar to that of subjects with alzheimer 's disease , whereas the memory performance of subjects with namci is similar to that of healthy elderly subjects . these authors concluded that the deficits are likely to be related to neuropathological disease processes that affect the neuronal navigation circuits . we observed striking changes in the way that our subjects with mci responded to the tests when they analysed their behaviour and strategies . the mcbt and the mwct rely on different cognitive functions , including encoding capabilities , planning strategies and memorisation . among these functions , we were particularly interested in the types of strategies used to solve the corsi test . we have established a graduated scale that ranges from the lack of a strategy to the use of the most appropriate strategies ( fig . 2 ) . there was no significant difference in the strategies used between the groups of older subjects in the performance on mcbt , but there were significant differences in the strategies used between the groups of older subjects in the performance on mwct . although the elderly appear to achieve the same performance ( measured by the span score ) , studying the strategies reveals pronounced deficits in subjects with mci . the errors of the healthy elderly subjects were primarily related to localisation , which are associated to an attention deficit . in addition , the strategies used by the subjects with mci during the tests were unsuitable and reflect their early deficits in spatial memory . thus , we assume that cognitive impairment can be evaluated in the elderly by studying their behaviour and the type of strategy that they used in our test . analysing such strategies could be a relevant way to differentiate between the subjects with mci and the healthy elderly subjects . the sudden loss of all information on the mwct could be related to an early alteration of neuronal circuits that are involved in human navigation . consequently , the evaluation of navigation skills in the mwct can help to identify mci subjects . the dual task test has recently been shown to be relevant to detect patients at risk for developing dementia . the test , which was used in the present study , evaluated navigation skills that can be rapidly performed ; it is also computerised and therefore evaluator independent . finally , we wanted to test the relationship that may exist between motor performance and visuospatial working memory . it is likely that the deficits shown on the mwct depend on decreased walking speed , which increases locomotion time in the elderly . when we evaluated the subjects ' spontaneous walking for 10 m and their working memory capacity in their performance in mwct , we observed a significant correlation between their motor performance but not in their performance in mcbt . thus , the differences observed between the young subjects and the mci subjects seem to be related to motor deficits . we hypothesise that the decrease in mwct performance with pathological ageing is primarily caused by cognitive impairment and motor deficits . however , limitations of the present study are the rather small number of included subjects and the disparity between women and men in all studied groups . several studies have shown that gender strongly influences spatial navigation performance , especially on the walct . additionally , our group of subjects with mci was heterogeneous and not large enough to permit subgroup analyses . unfortunately , our subjects were not checked by mri or by specific biomarkers to explore the state of their health . in the future , it will be interesting to explore how patients with dementia perform on the mwct to determine whether the information on topographical disorientation can be extracted . it would also be important to investigate whether this test has a predictive value on the onset of dementia or cognitive decline . brain and cognitive impairment associated with ageing creates difficulty in correctly performing tasks that require visuospatial working memory . although these deficits were more pronounced during the navigation task , it is clear that the span scores on the mcbt and the mwct do not identify early cognitive decline in subjects with mci . however , studying the strategies that subjects use to solve problems on the corsi tests and on the spatial navigation tests is a novel approach to differentiate between the cognitive performance in healthy elderly subjects and the cognitive performance in subjects with mci . this assessment appears to be a valuable tool for measuring the state of the neural circuits involved in spatial navigation . identifying the strategies used in these tests could be a useful marker for identifying subjects at risk for developing dementia .
backgroundsubjects with mild cognitive impairment ( mci ) have disturbances in their spatial navigation abilities and exhibit early deficits in visuospatial short - term memory . 
 the purpose of the present study was to determine whether a quantitative ( span score ) and qualitative ( evaluating navigation strategies used ) analysis of the corsi test ( usual condition and complex navigation task ) would be useful to reveal cognitive decline.methodswe evaluated the performance of 15 young adults , 21 healthy elderly subjects and 15 subjects with mci using the electronic version of the corsi test ( the modified corsi block - tapping test , mcbt ) and the complex navigation task ( the modified walking corsi test , mwct ) . 
 the mwct , which is an adaptation of the corsi test , assesses spatial memory when the subject walks in a complex environment . 
 we used richard et al . 
 's model [ cogn sci 1993;17:497 - 529 ] to investigate problem - solving strategies during the corsi tests.resultsthe span scores obtained on the mcbt and the mwct were significantly lower in the healthy elderly subjects ( mcbt = 5.0  0.7 ; mwct = 4.0  0.7 ) and the subjects with mci ( mcbt = 4.7  0.8 ; mwct = 4.1  0.9 ) than in the younger adults ( mcbt = 6.2  0.6 ; mwct = 5.3  1.0 ) . 
 the visuospatial working memory was more impaired in the complex navigation task ( mwct = 4.3  0.9 ) than in the modified corsi test ( mcbt = 5.3  0.8 ) . 
 finally , the subjects with greater cognitive impairment were more likely to have inadequate or absence of problem - solving strategies.conclusionsinvestigating the problem - solving strategies used during the mwct appears to be a promising way to differentiate between the subjects with mci and the healthy elderly subjects .