Patent Publication Number: US-2023141614-A1

Title: Cognitive impairment diagnostic device and cognitive impairment diagnostic program

Description:
TECHNICAL FIELD 
     The present invention relates to a cognitive impairment diagnostic device and a cognitive impairment diagnostic program for diagnosis of cognitive impairment. 
     BACKGROUND ART 
     The conventional technologies relating to devices for diagnosis of cognitive impairment include the technologies as described below. 
     Patent literature (PTL) 1 and PTL 2 propose medical diagnostic devices utilizing line-of-sight detection. Such medical diagnostic devices enable an objective diagnosis of brain function-related disorder by detecting head movement and eye movement of a subject. 
     PTL 3 proposes a system for detecting eye movements of a subject for diagnosis of neurological disease. 
     PTL 4 and PTL 5 propose eye test charts for examining an eye disease such as retinal and optic nerve diseases or examining an optical nerve disorder caused by, for example, an intracranial disease. 
     PTL 6 through PTL 9 propose autism diagnosis support systems for diagnosis of autism of a subject, using an eye-gaze detection unit that includes at least an imaging camera. 
     PTL 10 proposes a cerebral disorder diagnosis support device that detects line of sight and the pupils of a subject to determine the possibility of the subject having a cerebral disorder. 
      PTL 11 proposes a diagnosis support device capable of effectively supporting diagnosis of a visual perception disorder. 
     PTL 12 proposes an eyeball movement measuring device and measuring method capable of detecting an initial motion time of eye movement even from a rough image. 
     PTL 13 proposes a cognitive impairment diagnostic device that enables a simple, low-cost, objective, quantitative, and versatile diagnosis. 
     Citation List 
     Patent Literature 
     
         
         Japanese Unexamined Patent Application Publication No. 6-70884 
         Japanese Unexamined Patent Application Publication No. 6-70885 
         Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2016-523112 
         Japanese Patent No. 4560801 
         Japanese Patent No. 4116354 
         Japanese Patent No. 5926210 
         Japanese Patent No. 5912351 
         Japanese Patent No. 5761048 
         Japanese Patent No. 5761049 
         Japanese Patent No. 5817582 
         Japanese Unexamined Patent Application Publication No. 2017-158866 
         Japanese Unexamined Patent Application Publication No. 2017-176302 
         WO2019/098173 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In general, a cognitive functioning test (neurophysiological examination) in the form of face-to-face interview has been used for diagnosis of cognitive impairment and dementia. The cognitive functioning test is a method in which an examiner asks a subject some questions for assessing the cognitive function, scores the answers to the questions that are given orally or in the form of writing of characters and drawing of graphics, and calculates a cognitive function score. This method has a problem, however, that the test is time consuming. For example, even the simplest mini-mental state exam (MMSE) takes about 15 to 30 minutes. The method also has a problem that a subject experiences a significant psychological stress due to the nature of the test that is conducted in the form of face-to-face interview. Another problem is that scores largely vary depending on the difference in the skills of interviewing examiners and their interpretation of the answers to the questions. 
     To solve the foregoing problems, the present inventors propose the cognitive impairment diagnostic device of PTL 13. A new cognitive impairment diagnostic device is further awaited. 
     The present invention aims to provide a cognitive impairment diagnostic device and a cognitive impairment diagnostic program that achieve a simple, low-cost, objective, quantitative, and versatile diagnosis of cognitive impairment, using a new diagnostic method. 
     Solution to Problem 
     The cognitive impairment diagnostic device according to an aspect of the present invention includes: an obtainer that obtains a distribution map representing a distribution of gaze points of a subject on a movie for cognitive assessment; and a diagnoser that makes diagnosis of cognitive impairment, based on the distribution map. Here, the movie for cognitive assessment includes, in time order: a first movie including (i) a first region that includes an image for encoding that is displayed in a visually enhanced manner, and (ii) a plurality of second regions that include normal images that are displayed without being enhanced; and an assessment movie including (iii) a third region that includes an assessment image that is similar to the image for encoding and displayed at a same position as the image for encoding without being visually enhanced, and (iv) the plurality of second regions. The diagnoser: calculates, in a distribution map on the assessment movie, a percentage of fixation duration for which the third region is focused on; and makes diagnosis of suspected memory impairment when the percentage of fixation duration is lower than a threshold. 
     The cognitive impairment diagnostic program according to an aspect of the present invention is a cognitive impairment diagnostic program executed by a computer that obtains a distribution map representing a distribution of gaze points of a subject on a movie for cognitive assessment, and makes diagnosis of cognitive impairment, based on the distribution map. Here, the movie for cognitive assessment includes, in time order: a first movie including (i) a first region that includes an image for encoding that is displayed in a visually enhanced manner, and (ii) a plurality of second regions that include normal images that are displayed without being enhanced; and an assessment movie including (iii) a third region that includes an assessment image that is similar to the image for encoding and displayed at a same position as the image for encoding without being visually enhanced, and (iv) the plurality of second regions. The cognitive impairment diagnostic program causes the computer to execute: calculating, in a distribution map on the assessment movie, a percentage of fixation duration for which the third region is focused on; and making diagnosis of suspected memory impairment when the percentage of fixation duration is lower than a threshold. 
     Advantageous Effects of Invention 
     The cognitive impairment diagnostic device and the cognitive impairment diagnostic program according to an aspect of the present invention achieve a simple, low-cost, objective, quantitative, and versatile diagnosis of cognitive impairment. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1 A  is a block diagram showing an example configuration of the cognitive impairment diagnostic device according to an embodiment. 
         FIG.  1 B  is a block diagram showing another example configuration of the cognitive impairment diagnostic device according to the embodiment. 
         FIG.  2 A  is a diagram showing an example external view of the cognitive impairment diagnostic device according to the embodiment. 
         FIG.  2 B  is a diagram showing another example external view of the cognitive impairment diagnostic device according to the embodiment. 
         FIG.  3    is a diagram showing an example of the storage content of storage according to the embodiment. 
         FIG.  4    is a diagram showing an example of case characteristics data according to the embedment. 
         FIG.  5    is a flowchart of example diagnostic processes performed by the cognitive impairment diagnostic device according to the embodiment. 
         FIG.  6    is a flowchart of an example first diagnostic process according to the embodiment. 
         FIG.  7    is a diagram showing an example movie for cognitive assessment and so forth in the first diagnostic process shown in  FIG.  6   . 
         FIG.  8    is a diagram showing an example distribution map obtained in the first diagnostic process performed on a subject without memory impairment. 
         FIG.  9    is a diagram showing an example distribution map obtained in the first diagnostic process performed on a subject with memory impairment. 
         FIG.  10    is a flowchart of an example second diagnostic process according to the embodiment. 
         FIG.  11    is a diagram showing an example movie for cognitive assessment in the second diagnostic process shown in  FIG.  10    in which a linguistic instruction is used. 
         FIG.  12    is a diagram showing another example of the movie for cognitive assessment in the second diagnostic process shown in  FIG.  10    in which a linguistic instruction is used. 
         FIG.  13    is a diagram showing an example distribution map obtained in the second diagnostic process that is performed, using  FIG.  11   , on a subject without aphasia. 
         FIG.  14    is a diagram showing an example distribution map obtained in the second diagnostic process that is performed, using  FIG.  11   , on a subject with aphasia. 
         FIG.  15    is a diagram showing a first example of a movie for cognitive assessment in the second diagnostic process shown in  FIG.  10    in which no linguistic instruction is used. 
         FIG.  16    is a diagram showing an example assessment movie that corresponds to  FIG.  15   . 
         FIG.  17    is a diagram showing an example distribution map obtained in the second diagnostic process that is performed, using  FIG.  15   , on a subject without aphasia. 
         FIG.  18    is a diagram showing an example distribution map obtained in the second diagnostic process that is performed, using  FIG.  15   , on a subject with aphasia. 
         FIG.  19    is a diagram showing a second example of a movie for cognitive assessment in the second diagnostic process shown in  FIG.  10    in which no linguistic instruction is used. 
         FIG.  20    is a diagram showing an example assessment movie that corresponds to  FIG.  19   . 
         FIG.  21    is a diagram showing an example distribution map obtained in the second diagnostic process that is performed, using  FIG.  20   , on a subject without aphasia. 
         FIG.  22    is a diagram showing an example distribution map obtained in the second diagnostic process that is performed, using  FIG.  20   , on a subject with aphasia. 
         FIG.  23    is a flowchart of an example third diagnostic process according to the embodiment. 
         FIG.  24    is a diagram showing an example movie for cognitive assessment used in the third diagnostic process shown in  FIG.  23   . 
         FIG.  25    is a diagram showing an example assessment movie used in the third diagnostic process shown in  FIG.  23   . 
         FIG.  26    is a diagram showing an example distribution map in the third diagnostic process that is performed, using  FIG.  24   , on a subject without cognitive impairment. 
         FIG.  27    is a diagram showing a correlation between an MMSE score and the percentage of fixation duration for which an instruction sentence region in  FIG.  25    is focused on in the third diagnostic process. 
         FIG.  28    is a diagram showing a correlation between an MMSE score and the percentage of fixation duration for which an irrelevant incorrect image in  FIG.  25    is focused on in the third diagnostic process. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     An embodiment will be specifically described below with reference to the drawings. 
     An exemplary embodiment described below shows a general or specific example. The numerical values, shapes, materials, elements, the arrangement and connection of the elements, steps, the processing order of the steps etc. shown in the following exemplary embodiment are mere examples, and therefore do not limit the scope of the appended Claims and their equivalents. Therefore, among the elements in the following exemplary embodiment, those not recited in any one of the independent claims are described as optional elements. 
     Also note that the drawings are schematic diagrams, and thus are not necessarily illustrated precisely. Also, the same elements are assigned the same reference marks throughout the drawings. 
     Embodiment 
     The following describes the cognitive impairment diagnostic device and the cognitive impairment diagnostic program according to the embodiment with reference to the drawings. 
     1. Configuration of Cognitive Impairment Diagnostic Device 
       FIG.  1 A  is a block diagram showing an example configuration of the cognitive impairment diagnostic device according to the embodiment.  FIG.  2 A  is a diagram showing an example external view of the cognitive impairment diagnostic device according to the embodiment. 
     As shown in  FIG.  1 A , cognitive impairment diagnostic device  1  includes display  10 , imaging device  20 , and personal computer (PC)  30 . An example configuration of cognitive impairment diagnostic device  1  is shown here in which a commercially available general PC  30  serves as a primary control device to which display  10  and imaging device  20  are further added. 
     Display  10  is a flat-panel display including display surface  11 . Display  10  displays, on display surface  11 , a movie for assessing cognitive impairment. For the purpose of showing the movie for cognitive assessment to a subject, display  10  is an oversize liquid-crystal display or organic electroluminescence display, as shown in  FIG.  2 A , that is easy even for the elderly to see. Display  10  may also be a PC monitor. Alternatively, a commercially available oversize television may serve as a monitor. Instead of a flat-panel display, display  10  may include a screen and a projector as display surface  11 . 
     Imaging device  20  is a module attachable to display  10 . Imaging device  20  includes at least imager  21  for capturing an image of the eyes of a subject and light source unit  24 . 
     Imager  21  is a stereo camera including camera  22  and camera  23 . Camera  22  and camera  23  may each be, for example, an infrared camera. Another example of camera  22  and  23  may each be a visible camera. Note that imager  21  may not be a stereo camera, and thus may be a single camera, or three or more cameras. 
     Light source unit  24  includes light source  25  and light source  26  for radiating an infrared ray to a subject as illumination light. Each of light source  25  and light source  26  may include, for example, one or more infrared light emitting diodes (LEDs). Another example may be light source  25  and light source  26  that include one or more white LEDs. Note that when illumination is sufficiently bright in the environment in which a subject is present, imaging device  20  may not include light source unit  24 . Also, imaging device  20  may be attached to an upper portion of display  10  or separately attached on the right and left sides of display  10 . 
     PC  30  includes processor  31 , storage  32 , inputter  33 , outputter  34 , display  35 , interface  36 , detector  37 , generator  38 , and diagnoser  39 . Of the functional blocks shown in  FIG.  1 A , processor  31 , storage  32 , inputter  33 , outputter  34 , display  35 , and interface  36  are implemented by general hardware and software products of a commercially available computer. The other functional blocks, i.e., detector  37 , generator  38 , and diagnoser  39 , are structural elements that are mainly realized by processor  31  executing the cognitive impairment diagnostic program according to the present embodiment. 
     Processor  31  is what is known as a central processing unit (CPU) that executes a program stored in storage  32 . 
     Storage  32  stores programs to be executed by processor  31  and data items to be processed by processor  31 . Storage  32  further includes database  324 . The programs stored in storage  32  include the cognitive impairment diagnostic program according to the present embodiment in addition to software products such as various firmware, an operating system (OS), and driver software. The data items stored in storage  32  include movie data for cognitive assessment, case characteristics data, gaze point data, distribution map data, etc. The movie data for cognitive assessment is still images or a moving image generated for diagnosis of cognitive impairment. The case characteristics data is data representing the characteristics of gaze point distributions that are typical of cognitive impairment. The gaze point data is time-series data indicating the positions and times of gaze points detected by detector  37 . The distribution map is generated by generator  38  by sequentially plotting time-series gaze points in real time on a two-dimensional plane in accordance with the gaze point data. The distribution map shows a two-dimensional distribution of gaze points. 
     Note that storage  32  includes: a main memory or a primary memory that includes, for example, a dynamic random access memory (DRAM); an auxiliary memory or a secondary memory that includes, for example, a hard disc drive (HDD) device and a solid state drive (SSD) device; and a cache memory. Stated differently, the present description uses storage  32  as a generic name of the structural elements capable of storing programs and data. 
     Inputter  33  includes, for example, a keyboard, a mouse, a tack pad, etc. Inputter  33  receives an operation of an operator. 
     Outputter  34 , an example of which is a speaker, outputs sound. 
     Display  35  is, for example, a liquid-crystal display. Display  35  displays, for example, a movie for cognitive assessment on which a distribution map is superimposed for monitoring by the user (here, examiner). 
     Interface  36  is capable of performing communications via a cable, with display  10  and imaging device  20  connected. Interface  36  includes, for example, a high-definition multimedia interface (HDMI)® port and a universal serial bus (USB) port. In this case, interface  36  connects to display  10  via an HDMI® cable and connects to imager  21  and light source unit  24  via a USB cable. 
     Detector  37  detects the gaze points of a subject on display surface  11  on the time series, on the basis of images captured by imager  21 . For example, detector  37  detects the eye gaze of the subject from an image captured by imager  21  and detects, as the position of a gaze point, the coordinates of the point at which the eye gaze intersects with display surface  11 . The positions of gaze points are detected at regular time intervals. The regular time intervals may be set between several 10 mS and several 100 mS, and thus may be, for example, 100 mS. Detector  37  generates, in real time, a group of coordinate data items (x, y, t) that include time as gaze point data representing the position of a time-series gaze point. Here, “x” and “y” are coordinates on a plane (e.g., display surface  11  or movie for cognitive assessment) and “t” is time. 
     Generator  38  generates a distribution map that represents the distribution of the gaze points detected by detector  37 . The distribution map is, for example, a map on which marks (e.g., colored dots) corresponding to the foregoing coordinate data (x, y, t) are plotted on a two-dimensional plane. The distribution map is superimposed, in real time, on the movie for cognitive assessment that is displayed on display  35  of PC  30 . Such marks may be displayed in a manner, for example, that a newer gaze point is brighter. 
     Diagnoser  39  makes diagnosis of the cognitive function of the subject by determining whether the distribution map has the characteristics of those indicated by the case characteristics data. 
     As described above, cognitive impairment diagnostic device  1  includes: display  10  that displays, on display surface  11 , a movie for assessing cognitive impairment; imager  21  that captures an image of the eyes of a subject; detector  37  that detects, on the time series, gaze points of the subject on display surface  11 , on the basis of the image captured by imager  21 ; generator  38  that generates a distribution map representing a distribution of the gaze points detected by detector  37 ; storage  32  that stores case characteristic data  310  indicating the characteristics of the gaze point distribution that are typical of cognitive impairment; and diagnoser  39  that makes diagnosis of cognitive impairment of the subject by determining whether the distribution map has the characteristics indicated by case characteristics data  310 . 
     With the foregoing configuration, it is possible to enable cognitive impairment diagnostic device  1  to make a simple, low-cost, objective, quantitative, and versatile diagnosis of cognitive function. 
     Note that PC  30  shown in  FIG.  1 A  and  FIG.  2 A  may be any one of a notebook computer, a tablet computer, or a desktop computer. 
     The following describes another example configuration of cognitive impairment diagnostic device  1 . 
       FIG.  1 B  is a block diagram showing another example configuration of cognitive impairment diagnostic device  1  according to the embodiment.  FIG.  1 B  is different from  FIG.  1 A  in that display  10 , imager  20 , detector  37 , and generator  38  are deleted, and that obtainer  41  is added. The following avoids overlapping description of the common points and mainly describes the differences. 
     Display  10 , imager  20 , detector  37 , and generator  38  in  FIG.  1 A  correspond to the elements for eye tracking for generating distribution map data that represents the distribution of gaze points of a subject on the movie for cognitive assessment. In an example configuration shown in  FIG.  1 B , major elements for diagnosis of cognitive impairment are shown, with the elements for generating the distribution map data separated from  FIG.  1 A . 
     Obtainer  41  obtains the distribution map data generated by an external device, and stores it in storage  32 . Such distribution map data is subjected to diagnosis of cognitive impairment. 
     Note that obtainer  41  is simply required to be capable of obtaining, from an external device, distribution map data, movie data for cognitive assessment, case characteristics data, and gaze point data. When movie data for cognitive assessment, case characteristics data, etc. that correspond to the distribution map data are already stored in storage  32 , for example, obtainer  41  may obtain only the distribution map data. Also, for example, obtainer  41  may obtain, for the first subject, distribution map data, movie data for cognitive assessment, case characteristics data, and gaze point data corresponding to such subject, and obtain only distribution map data for the second and subsequent subjects. 
     Note that cognitive impairment diagnostic device  1  shown in  FIG.  1 A  may further include obtainer  41  shown in  FIG.  1 B . 
     Also, the external device is simply required to be capable of generating a distribution map that represents the distribution of time-series gaze points of a subject by eye tracking, and thus an eye tracking method and a configuration for generating a distribution map are not limited to specific ones. Also, the external device may be connected to cognitive impairment diagnostic device  1  via the Internet, a phone line, or a dedicated line. 
     Note that cognitive impairment diagnostic device  1  is not required to be a device having oversize display  10  as shown in an example external view in  FIG.  2 A , and thus may be configured as a smart device. 
       FIG.  2 B  is a diagram showing another example external view of cognitive impairment diagnostic device  1 . Cognitive impairment diagnostic device  1  in this diagram is a tablet smart device having the same functional structural elements as those shown in  FIG.  1 A , such as display  10  and imager  22 . 
     Display  10  shown in  FIG.  2 B  doubles as display  10  and display  35  of PC  30  shown in  FIG.  2 A . A touch panel is provided on a surface of display surface  11 . 
     Imager  22  is a front camera of the smart device. Imager  22  is used, for example, for eye tracking by detecting eye positions and movements by a face recognition technology. In this case, light source unit  24  may not be included. Movie display for a subject is performed on display  10 . Also, in accordance with a touch panel operation performed by the examiner, the cognitive impairment diagnostic program is executed by the processor inside of the tablet device. The smart device makes diagnosis of cognitive impairment by being alternately used by the subject and the examiner or by the examiner showing display  10  to the subject. 
     Cognitive impairment diagnostic device  1  as the foregoing smart device may be implemented, for example, by a tablet terminal, a smartphone, or a notebook PC. Also, the cognitive impairment diagnostic program is prepared as an app of these devices. Also note that cognitive impairment diagnostic device  1  shown in  FIG.  2 B  may have the same functional structural elements as those shown in  FIG.  1 B . 
     1.1 Program and Data in Storage 32 
     The following describes programs and data stored in storage  32 . 
       FIG.  3    is a diagram showing an example of the storage content in storage  32  according to the embodiment. In the diagram, storage  32  stores movie data for cognitive assessment  300 , case characteristics data  310 , program  320 , gaze point data  322 , and distribution map data  323 . Program  320  includes cognitive impairment diagnostic program  321 . Storage  32  further includes database  324 . 
     Movie data for cognitive assessment  300  is a set of movie data items including first movie data  301  through third movie data  303 . Each of the movie data items is a movie generated for diagnosis of the presence or absence of cognitive impairment or the level of cognitive impairment, or a movie generated for distinguishing cases of cognitive impairment. 
     Case characteristics data  310  is data that represents the characteristics of gaze point distributions that are typical of cognitive impairment. Case characteristics data  310  is a set of characteristic data items including first characteristics data  311  through third characteristics data  313 . First characteristics data  311  through third characteristics data  313  correspond to first movie data  301  through third movie data  304 , respectively. 
     Program  320  includes software products, such as various firmware, an operating system (OS), and driver software, and cognitive impairment diagnostic program  321 . Cognitive impairment diagnostic program  321  is a program executed by a computer, i.e., PC  30 . Cognitive impairment diagnostic program  321  causes the computer to execute: displaying, on display surface  11 , a movie for cognitive assessment for cognitive impairment; capturing, by imager  32 , an image of the eyes of a subject; detecting, on the time series, gaze points of the subject on display surface  11 , on the basis of the image captured by imager  21 ; generating a distribution map representing a distribution of the detected gaze points; and making diagnosis of cognitive impairment of the subject by determining whether the distribution map has the characteristics indicated by case characteristics data. Of these, the detecting, performed by PC  30 , of the gaze points of the subject on display surface  11  on the time series, on the basis of the image captured by imager  21  is a function of detector  37 . The generating, performed by PC  30 , of the distribution map that represents the distribution of the detected gaze points is a function of generator  38 . The making of diagnosis, performed by PC  30 , of cognitive impairment of the subject by determining whether the distribution map has the characteristics indicated by the case characteristics data is a function of diagnoser  39 . 
     Gaze point data  322  is time-series data representing the positions and times of the gaze points detected by detector  37 . Gaze point data  322  is, for example, a set of coordinate data (x, y, t) that includes time as described earlier. 
     Distribution map data  323  is data that represents the distribution map as described earlier. 
     Database  324  stores various data items and others. Note that database  324  may not be a part of storage  32 , and thus may be provided outside of storage  32 . Database  324  may also be connected via a network such as the Internet. 
     Note that in addition to the program and the data items shown in  FIG.  3   , storage  32  also stores diagnostic data indicating the diagnostic result of each subject, and data that associates, with one another, gaze point data  322 , distribution map data  323 , and the diagnosis data of each subject. 
     Next, specific examples of case characteristics data  310  will be described. 
       FIG.  4    is a diagram showing an example of case characteristics data  310  according to the embodiment. Case characteristics data  310  shown in this diagram includes first characteristics data  311  through third characteristics data  313 .  FIG.  4    shows the respective characteristics of first characteristics data  311  through third characteristics data  313  and their corresponding cases of cognitive impairment. 
     First characteristics data  311  associates the first characteristics and memory impairment. The first characteristics are typical characteristics of a person with memory impairment. More specifically, the first characteristics indicate the characteristics that the percentage of fixation duration (hereinafter also referred to as “% fixation duration”) for which a memory-recalling image is focused on is low on a distribution map of gaze points when such memory-recalling image is presented to a person with memory impairment after the presentation of a movie for encoding. A precondition of the first characteristics is that a movie for encoding, which is the movie for cognitive assessment of first movie data  301 , is presented to a subject, after which a memory-recalling image is further presented to the subject. 
     Second characteristics data  312  associates the second characteristics and aphasia. Stated differently, the second characteristics are typical characteristics of a person with aphasia. More specifically, the second characteristics indicate the characteristics that the % fixation duration for which a correct image is focused on is low on a distribution map of gaze points in an image that includes a plurality of alternatives including the correct image and an incorrect image. A precondition of the second characteristics is that a second movie, which is the movie for cognitive assessment of second movie data  302 , is being presented to a subject. 
     Third characteristics data  313  associates the third characteristics and cognitive impairment. Stated differently, the third characteristics are typical characteristics of a person with cognitive impairment. More specifically, the third characteristics indicate the characteristics that the % fixation duration for which an incorrect image is focused on is no small on a distribution map of gaze points in an image including a plurality of alternatives including a correct image and the incorrect image. A precondition of the third characteristics is that a third movie, which is the movie for cognitive assessment of third movie data  303 , is being presented to a subject. 
     1.2 Example Processes of Cognitive Impairment Diagnostic Device 1 
     The following describes example processes performed by cognitive impairment diagnostic device  1  according to the embodiment with the foregoing configuration. 
       FIG.  5    is a flowchart of example diagnostic processes performed by cognitive impairment diagnostic device  1  according to the embodiment. 
     As shown in  FIG.  5   , cognitive impairment diagnostic device  1  sequentially performs a first diagnostic process (S 10 ) through a third diagnostic process (S 30 ). Example diagnostic processes shown in  FIG.  5    are processes mainly realized by PC  30  executing cognitive impairment diagnostic program  321 . 
     The first diagnostic process is a diagnostic process that uses first movie data  301  and first characteristics data  311 . The second diagnostic process is a diagnostic process that uses second movie data  302  and second characteristics data  312 . The third diagnostic process is a diagnostic process that uses third movie data  303  and third characteristics data  313 . 
     The duration of each of the first diagnostic process through the third diagnostic process is on the order of 0.5 minutes to a few minutes. 
     Note that the order of the first diagnostic process through the third diagnostic process may be different from the one shown in  FIG.  5   . 
     In  FIG.  5   , at least one of the first diagnostic process through the third diagnostic process may be selected and performed. 
     Note that a calibration process for gaze point detection may be performed before starting the example diagnostic processes shown in  FIG.  5   . 
     2.1 First Diagnostic Process 
     The following describes in detail the first diagnostic process in step S 10  shown in  FIG.  5   . The first diagnostic process uses the foregoing first characteristics to make diagnosis of memory impairment. 
       FIG.  6    is a flowchart of an example of the first diagnostic process (S 10 ) according to the embodiment.  FIG.  7    is a diagram showing an example movie for cognitive assessment and so forth used in the first diagnostic process shown in  FIG.  6   . 
     As shown in  FIG.  6   , PC  30  starts the detection of gaze points by detector  37  (S 61 ), and executes loop  1  (S 62  through S 65 ), which is processing for causing a subject to remember the region of a specific image or characters. 
     In loop  1 , PC  30  displays a movie for cognitive assessment for encoding (S 63 ), and displays another movie immediately after that (S 64 ). N, which is the number of iterating loop  1 , may be  2  or more. 
     In step S 63 , the movie for encoding is presented that induces the eye gaze of the subject to unconsciously focus on a specific graphic or region on the screen, that is, without an intervention of a linguistic instruction. In an example shown in  FIG.  7   , the movie for cognitive assessment includes movie for encoding  b   11  and movie for encoding  b   12  in time order. Movie for encoding  b   11  is displayed for Ta seconds, immediately after which movie for encoding  b   12  is displayed for Tb seconds. For example, time Ta may be on the order of five seconds and time Tb may be on the order of three seconds. 
     Movie for encoding  b   11  includes a total of 20 clock images, of which 10 are at an upper portion and the other 10 are at a lower portion of display surface  11 . Of these 20 clock images, only the second right clock image M 1  in the bottom line is rotating. This rotation may either be a high-speed rotation of the clock hands or the rotation of the clock image itself. The other 19 clock images stay still to attract the attention of the subject to clock image M 1 . 
     In movie for encoding  b   12 , a dotted line frame is added to enhance only the rotating clock image M 1  and the other clock images disappear. This is to attract the attention of the subject to clock image M 1  without using a linguistic instruction. 
     In step S 64 , another movie is displayed for Tc seconds as an interval in the memorization. Tc may be, for example, on the order of 60 seconds. 
     Display times Td, Te, and Tf in the second iteration in  FIG.  7    may be the same as or different from times Ta, Tb, and Tc in the first iteration. 
     Such iteration of loop  1  causes the subject to unconsciously focus his/her attention on clock image M 1  on the screen, thereby augmenting the memory. 
     After loop  1 , PC  30  displays assessment movie  b   3  for recalling the memory for Tg seconds (S 66 ). Time Tg may be, for example, on the order of five seconds. Assessment movie  b   3  shown in  FIG.  7    includes clock image M 3  instead of clock image M 1 . Stated differently, assessment movie  b   3 , in which all of the 20 clock images stay still, is originally configured not to attract the attention only to a specific graphic. 
     A subject without memory impairment remembers the contents of the movie for encoding (movie for encoding  b   11  and movie for encoding  b   12 ) that such subject has viewed, and thus unconsciously focuses the eye gaze at the specific graphic or region on which his/her attention was focused in the movie for encoding. The specific graphic or region, which is a graphic or region that the subject has memorized from the movie for encoding, is still clock image M 3  located at the same position as clock image M 1  in  FIG.  7   . 
     In contrast, a subject with memory impairment cannot retain his/her memory or remember the contents, and thus tends to view randomly without unconsciously focusing the eye gaze at clock image M 3 . 
     Subsequently, to quantitatively assess the memory power, PC  30  sets, as a region of interest, a specific graphic or region in the assessment movie for recalling the memory and calculates, as a score of the memory power, % fixation duration Vb for which the region of interest is focused on (S 67 ). Here, % fixation duration Vb may be the percentage (%) of the presence of gaze points on the region of clock image M 3 , which is the region of interest, in the distribution pattern of gaze points on the assessment movie. 
     PC  30  further determines whether % fixation duration Vb calculated is greater than threshold th1 (S 68 ). When determining that % fixation duration Vb is greater than threshold th1, the subject is diagnosed as having no memory impairment (S 69 ). 
     PC  30  further determines whether % fixation duration Vb calculated is lower than threshold th1 and greater than threshold th2 (S 70 ). When determining that % fixation duration Vb is lower than threshold th1 and greater than threshold th2, the subject is diagnosed as having suspected memory impairment (S 71 ). 
     PC  30  further determines whether % fixation duration Vb calculated is lower than threshold th2 (S 72 ). When determining that % fixation duration Vb is lower than threshold th2, the subject is diagnosed as having memory impairment (S 73 ). 
     Threshold th1 and threshold th2 can be appropriately set by calculating % fixation duration Vb of a plurality of subjects who are known beforehand whether having or not having memory impairment. 
     Note that  FIG.  6    shows an example of outputting three diagnostic results of “having no memory impairment”, “having suspected memory impairment”, and “having memory impairment”, but the diagnostic results are not limited to these. The diagnostic results thus may come in two types indicating the presence or absence of memory impairment, or may be four or more types indicating the presence or absence of memory impairment and the level of memory impairment. 
     Note that the flowchart of  FIG.  6    may include, instead of steps S 61  through S 66 , a step of obtaining a distribution map that represents the distribution of gaze points of a subject on the movie for cognitive assessment. The flowchart in which such steps are replaced by the step of obtaining the distribution map is easily implemented by PC  30  shown in  FIG.  1 B  or may be implemented by PC  30  shown in  FIG.  1 A . Next, an example of the distribution map obtained in the first diagnostic process will be described. 
       FIG.  8    is a diagram showing an example distribution map obtained in the first diagnostic process performed on a subject without memory impairment and having an MMSE score of 30.  FIG.  9    is a diagram showing an example distribution map obtained in the first diagnostic process performed on a subject with memory impairment and having an MMSE score of 14. Note that a perfect MMSE score is 30. The score 30 indicates that a person is cognitively unimpaired. The lower the score, the more severe cognitive impairment. 
       FIG.  8    and  FIG.  9    each show an example in which a distribution map is superimposed on each of movie for encoding  b   11 , movie for encoding  b   12 , and assessment movie  b   3  to be displayed on display  35  of PC  30 . 
     In movie for encoding  b   11  and movie for encoding  b   12 , as shown in  FIG.  8    and  FIG.  9   , gaze points of the subject concentrate on clock image M 1 . Movie for encoding  b   11  and movie for encoding  b   12  are movies for cognitive assessment each including: a first region including clock image M 1  that is an image for encoding and displayed in a visually enhanced manner; and a plurality of second regions including still clock images that are normal images displayed without being enhanced. As shown in  FIG.  8    and  FIG.  9   , the gaze points, on the movies for encoding, of the subjects with and without memory impairment are almost the same; their gaze points concentrate on clock image M 1  in the first region. 
     The gaze point distribution, on assessment movie  b   3  shown in  FIG.  8   , of the subject without memory impairment exhibits a high % fixation duration of 81% for clock image M 3  of the region of interest, as a result of the effect of the memorization. 
     In contrast, the gaze point distribution, on assessment movie  b   3  shown in  FIG.  9   , of the subject with memory impairment exhibits a % fixation duration of 0% for clock image M 3  of the region of interest, without any effects of the memorization. 
     In the first diagnostic process, memory impairment is diagnosed by quantitatively assessing the memory level of a subject to obtain, as a score of the memory power, a % fixation duration for which the region of interest on the assessment movie for recalling the memory is focused on. 
     As described above, the cognitive impairment diagnostic device that performs the first diagnostic process includes: obtainer  41  that obtains a distribution map representing a distribution of gaze points of a subject on a movie for cognitive assessment; and diagnoser  39  that makes diagnosis of cognitive impairment, based on the distribution map. Here, the movie for cognitive assessment includes, in time order: a first movie including (i) a first region that includes an image for encoding that is displayed in a visually enhanced manner, and (ii) a plurality of second regions that include normal images that are displayed without being enhanced; and an assessment movie including (iii) a third region that includes an assessment image that is similar to the image for encoding and displayed at a same position as the image for encoding without being visually enhanced, and (iv) the plurality of second regions. Diagnoser  39  calculates, in a distribution map on the assessment movie, a percentage of fixation duration for which the third region is focused on, and makes diagnosis of suspected memory impairment when the percentage of fixation duration is lower than a threshold. 
     Also, the cognitive impairment diagnostic device that performs the first diagnostic process includes: display  10  including a display surface; imager  21  that captures an image of the eyes of a subject; detector  37  that detects, on the time series, gaze points of the subject on the display surface, on the basis of the image captured by imager  21 ; generator  38  that generates a distribution map representing a distribution of the gaze points detected by detector  37 ; and diagnoser  39  that makes diagnosis of cognitive impairment, on the basis of the distribution map. Here, diagnoser  39  causes display  10  to display a first movie that includes a first region including an image for encoding that is displayed in a visually enhanced manner, and a plurality of second regions including normal images that are displayed without being enhanced. Diagnoser  39  further causes display  10  to display an assessment movie that includes a third region including an assessment image that is similar to the image for encoding and displayed at a same position as the image for encoding without being visually enhanced, and the plurality of second regions. Then, diagnoser  30  calculates, in the distribution map on the assessment movie, the percentage of fixation duration for which the third region is focused on, and makes diagnosis of suspected memory impairment when the percentage of fixation duration is lower than a threshold. 
     With this, it is possible to provide a cognitive impairment diagnostic device capable of making a simple, low-cost, objective, quantitative, and versatile diagnosis of memory impairment among cognitive impairments. What is more, it is possible to make the diagnosis without using an instruction by text and instruction by voice. This enables the diagnosis to be made on a plurality of subjects having different mother languages. Further, memory impairment is diagnosed within a mere few minutes. 
     Here, the first movie may include a first movie for encoding and a second movie for encoding in time order, the first movie for encoding including the first region and the plurality of second regions, the second movie for encoding including the first region and not including the plurality of second regions. 
     With this, it is possible to augment the ability of the subject to remember the first region. 
     Here, the movie for cognitive assessment may include an other movie that is displayed between the first movie and the assessment movie. 
     With this, it is possible to more distinctively determine whether the subject is capable of retaining the memory power by providing a period of displaying another movie between the memorization and the assessment. This thus increases the reliability of the diagnostic result. 
     Here, the movie for cognitive assessment may include a movie in which the first movie and the other movie are repeated two or more times. 
     With this, it is possible to augment the ability of the subject to remember the first region by such repetition. 
     Also, the cognitive impairment diagnostic program that performs the first diagnostic process is a cognitive impairment diagnostic program executed by a computer that obtains a distribution map representing a distribution of gaze points of a subject on a movie for cognitive assessment, and makes diagnosis of cognitive impairment, based on the distribution map. Here, the movie for cognitive assessment includes, in time order: a first movie including (i) a first region that includes an image for encoding that is displayed in a visually enhanced manner, and (ii) a plurality of second regions that include normal images that are displayed without being enhanced; and an assessment movie including (iii) a third region that includes an assessment image that is similar to the image for encoding and displayed at a same position as the image for encoding without being visually enhanced, and (iv) the plurality of second regions. Such cognitive impairment diagnostic program causes the computer to execute: calculating, in a distribution map on the assessment movie, a percentage of fixation duration for which the third region is focused on; and making diagnosis of suspected memory impairment when the percentage of fixation duration is lower than a threshold. 
     Also, the cognitive impairment diagnostic program that performs the first diagnostic process is a cognitive impairment diagnostic program executed by a computer that includes: display  10  including a display surface; imager  21  that captures an image of the eyes of a subject; detector  37  that detects, on the time series, gaze points of the subject on the display surface, on the basis of the image captured by imager  21 ; a generator that generates a distribution map representing a distribution of the gaze points detected by detector  37 ; and diagnoser  39  that makes diagnosis of cognitive impairment, on the basis of the distribution map. Such cognitive impairment diagnostic program causes the computer to execute: causing display  10  to display a movie for cognitive assessment that includes a first region including an image for encoding that is displayed in a visually enhanced manner, and a plurality of second regions including normal images that are displayed without being enhanced; further causing display  10  to display an assessment movie that includes a third region including an assessment image that is similar to the image for encoding and displayed at a same position as the image for encoding without being visually enhanced, and the plurality of second regions; calculating, in the distribution map on the assessment movie, the percentage of fixation duration for which the third region is focused on, and making diagnosis of suspected memory impairment when the percentage of fixation duration is lower than a threshold. 
     2.2.1 Second Diagnostic Process (Example of Using Linguistic Instruction) 
     Next, the second diagnostic process in step S 20  shown in  FIG.  5    in which a linguistic instruction is used will be described. The second diagnostic process uses the foregoing second characteristics to make diagnosis of aphasia. 
       FIG.  10    is a flowchart of an example of the second diagnostic process according to the embodiment.  FIG.  11    is a diagram showing an example movie for cognitive assessment in the second diagnostic process in  FIG.  10    in which a linguistic instruction is used. 
     In  FIG.  10   , PC  30  starts the detection of gaze points by detector  37  (S 101 ), displays the movie for cognitive assessment on display surface  11  (S 102 ), and calculates % fixation duration Vc for which the correct region is focused on in the movie for cognitive assessment (S 103 ). 
     The movie for cognitive assessment here is a movie that includes a first region including a correct character image and a plurality of second regions including incorrect character images. 
     In an example shown in  FIG.  11   , movie for cognitive assessment  c   11  is displayed for Ta seconds, after which movie for cognitive assessment  c   12  is displayed for Tb seconds. Time Ta and time Tb may each be, for example, on the order of 5 seconds to 10 seconds. 
     Movie for cognitive assessment  c   11  includes a clock image at a central portion, around which four regions serving as alternatives are included. Movie for cognitive assessment  c   12  is different from movie for cognitive assessment  c   11  in that an instruction sentence is laid over the clock image at the central portion. The instruction sentence reads “What is the name of this?”. The four regions around the instruction sentence include the first region including the correct character image “ ”(a Japanese word for “clock”) a and the plurality of second regions including incorrect character images “ .” (Japanese word for “tomato”), “ ” (Japanese word for “shrimp”), and “ ” (Japanese word for “wool yarn”). 
     As described above, the movie for cognitive assessment includes, for example, a plurality of regions serving as alternatives that include an image of a known object, and correct and incorrect names of such object. The number of alternatives is not limited to a specific number. The movie for cognitive assessment also shows an instruction sentence that reads “What is the name of this?”. The subject is prompted to gaze at the correct alternative by the instruction sentence. 
     Note that one movie for cognitive assessment  c   13  as shown in  FIG.  12    may be displayed instead of two movie for cognitive assessments  c   11  and  c   12  shown in  FIG.  11   . 
     Further, PC  30  calculates % fixation duration Vc for which the first region that includes the correct character image is focused on, after displaying the movie for cognitive assessment (S 103 ). Here, % fixation duration Vc may be the percentage (%) of the presence of gaze points in the first region in the distribution pattern of gaze points on the movie for cognitive assessment. 
     Next, PC  30  determines whether % fixation duration Vc calculated is greater than threshold th3 (S 104 ). When determining that % fixation duration Vc is greater than threshold th3, the subject is diagnosed as having no aphasia (S 105 ). 
     PC  30  further determines whether % fixation duration Vc calculated is lower than threshold th3 and greater than threshold th4 (S 106 ). When determining that % fixation duration Vc is lower than threshold th3 and greater than threshold th4, the subject is diagnosed as having suspected aphasia (S 107 ). 
     PC  30  further determines whether % fixation duration Vc calculated is lower than threshold th4 (S 108 ). When determining that % fixation duration Vc is lower than threshold th4, the subject is diagnosed as having aphasia (S 109 ). 
     Threshold th3 and threshold th4 can be appropriately set by calculating % fixation duration Vc of a plurality of subjects who are known beforehand whether having or not having aphasia. 
     Note that the flowchart of  FIG.  10    may include, instead of steps S 101  and S 102 , a step of obtaining a distribution map that represents the distribution of gaze points of a subject on the movie for cognitive assessment. The flowchart in which such steps are replaced by the step of obtaining the distribution map is easily implemented by PC  30  shown in  FIG.  1 B  or may be implemented by PC  30  shown in  FIG.  1 A . 
     Note that  FIG.  10    shows an example of outputting three diagnostic results of “having no aphasia”, “having suspected aphasia”, and “having aphasia”, but the diagnostic results are not limited to these. The diagnostic results thus may come in two types indicating the presence or absence of aphasia, or may be four or more types indicating the presence or absence of aphasia and the level of aphasia. 
     Next, an example of the distribution map obtained in the second diagnostic process will be described. 
       FIG.  13    is a diagram showing an example distribution map obtained in the second diagnostic process performed on a subject without aphasia and having an MMSE score of 30.  FIG.  14    is a diagram showing an example distribution map obtained in the second diagnostic process performed on a subject with aphasia and having an MMSE score of 14. 
     The gaze point distribution, on movie for cognitive assessment  c   12  shown in  FIG.  13   , of a subject without aphasia exhibits a high % fixation duration for which first region  c   111  that includes the correct character image is focused on. 
     In contrast, the gaze point distribution, on movie for cognitive assessment  c   12  shown in  FIG.  14   , of a subject with aphasia exhibits a low % fixation duration for which the first region that includes the correct character image is focused on. 
     When % fixation duration Vc for which the first region serving as the correct answer is focused on exceeds threshold th3, it can be determined that the answer to the instruction sentence is correct, that is, object naming ability is normal. Stated differently, a subject without aphasia is capable of focusing on the correct alternative “ ” at a rate of the threshold or greater. In contrast, a subject with aphasia has a relatively high rate of focusing on an alternative other than the correct answer. It is thus possible in the second diagnostic process to make diagnosis of whether a subject has aphasia and the level of aphasia, using as a measure, the % fixation duration for which the correct alternative is focused on. 
     2.2.2 Second Diagnostic Process (First Example Using No Linguistic Instruction) 
     An example of the second diagnostic process in which a linguistic instruction is used has been described above. Next, a first example of using no linguistic instruction in the second diagnostic process will be described. 
       FIG.  15    is a diagram showing the first example of a movie for cognitive assessment in the second diagnostic process shown in  FIG.  10    in which no linguistic instruction is used. 
     Movie for cognitive assessment  c   21  in  FIG.  15   , which shows an example display on display surface  11  for a subject, includes a correct region including characters having a meaning and incorrect regions including characters having no meaning. More specifically, movie for cognitive assessment  c   21  includes a plurality of characters arranged in matrix. The correct region corresponds to a row or column that includes characters having a meaning. Incorrect regions correspond to rows or columns that include characters having no meaning. The row that includes characters “ ” (the name of a Japanese sweet) is the correct region. The other rows and columns are incorrect regions including no characters having a meaning. 
       FIG.  16    is a diagram showing an example assessment movie that corresponds to  FIG.  15   .  FIG.  16    shows an example display on display  35  for the operator. In  FIG.  16   , correct region  c   211  serving as an assessment region is specified by a broken line frame compared to movie for cognitive assessment  c   21  shown in  FIG.  15   . 
     Next, an example gaze point distribution of a subject on movie for cognitive assessment  c   21  shown in  FIG.  15    will be described. 
       FIG.  17    is a diagram showing an example distribution map obtained in the second diagnostic process that is performed, using  FIG.  15   , on a subject without aphasia and having an MMSE score of 30.  FIG.  18    is a diagram showing an example distribution map obtained in the second diagnostic process that is performed, using  FIG.  15   , on a subject with aphasia and having an MMSE score of 14. 
     The gaze point distribution, on movie for cognitive assessment  c   21  shown in  FIG.  17   , of the subject without aphasia exhibits a high % fixation duration for which correct region  c   211  is focused on. 
     In contrast, the gaze point distribution, on movie for cognitive assessment  c   21  shown in  FIG.  18   , of the subject with aphasia tends to be random irrelevantly to correct region  c   211 . 
     In movie for cognitive assessment  c   21 , characters are arranged in matrix or in a grid pattern, in which “characters as a sequence of characters having a meaning” is present only in a specific portion. The other portions include no characters as a sequence of characters having a meaning when read from any directions. 
     When such characters in matrix are displayed, a subject without aphasia is capable of finding characters having a meaning therefrom. A % fixation duration of such subject focusing on the corresponding portion becomes automatically high. 
     Meanwhile, a subject with aphasia is incapable of finding characters as a sequence of characters having a meaning, and thus tends to view the entire screen randomly. A % fixation duration of such subject focusing on the specific portion thus does not become high relatively. In view of this, it is possible in the second diagnostic process to perform an objective diagnosis of aphasia, using as a measure, whether the % fixation duration for which a portion corresponding to the characters as a sequence of characters having a meaning (i.e., correct region) is focused on exceeds a threshold. 
      Characters including 3×3 hiragana characters are displayed on movie for cognitive assessment  c   21  shown in  FIG.  15   , in which characters having a meaning “ ” is recognizable when the three characters in the bottom line are read from left to right. The other sequences of characters are characters basically having no meaning. While no text or voice is provided as an instruction sentence to prompt a subject to find “ ”, the % fixation duration of a cognitively unimpaired person without aphasia focusing on the characters as a sequence of characters having a meaning “ ” automatically rises relatively. 
     In contrast, a subject with aphasia is incapable of recognizing such characters as a sequence of characters having a meaning and tends to view another region or view the entire screen randomly, with no rise in the % fixation duration for which “ ” is focused on. 
     2.2.3 Second Diagnostic Process (Second Example Using No Linguistic Instruction) 
     Next, a second example of using no linguistic instruction in the second diagnostic process will be described. 
       FIG.  19    is a diagram showing the second example of a movie for cognitive assessment in the second diagnostic process shown in  FIG.  10    in which no linguistic instruction is used.  FIG.  20    is a diagram showing an example assessment movie that corresponds to  FIG.  19   . 
     Movie for cognitive assessment  c   31  shown in  FIG.  19   , which shows an example display on display surface  11  for a subject, includes a correct region including characters having a meaning and incorrect regions including characters having no meaning. More specifically, in movie for cognitive assessment  c   31 , the row that includes characters “ ” (Japanese festival known as the Star Festival) is the correct region and the other rows and columns are incorrect regions including no characters having a meaning. 
       FIG.  20    shows an example display on display  35  for the operator. In  FIG.  20   , correct region  c   311  serving as an assessment region is specified by a broken line frame compared to movie for cognitive assessment  c   31  shown in  FIG.  19   . 
     Next, an example gaze point distribution of a subject on movie for cognitive assessment  c   31  shown in  FIG.  19    will be described. 
       FIG.  21    is a diagram showing an example distribution map obtained in the second diagnostic process that is performed, using  FIG.  20   , on a subject without aphasia and having an MMSE score of 30.  FIG.  22    is a diagram showing an example distribution map obtained in the second diagnostic process that is performed, using  FIG.  20   , on a subject with aphasia and having an MMSE score of 14. 
     The gaze point distribution on movie for cognitive assessment  c   31  shown in  FIG.  21    of the subject without aphasia exhibits a high % fixation duration for which correct region  c   311  is focused on. In contrast, the gaze point distribution on movie for cognitive assessment  c   31  shown in  FIG.  22    of the subject with aphasia tends to be random irrelevantly to correct region  c   311 . 
     Characters including 4×4 hiragana characters are displayed in movie for cognitive assessment  c   31  shown in  FIG.  19   , in which characters having a meaning “ ” is recognizable when the four characters in the second right column are read from top to bottom. The other sequences of characters are characters basically having no meaning. While no text or voice is provided as an instruction sentence to prompt a subject to find “ ”, the % fixation duration of a cognitively unimpaired person without aphasia focusing on the characters “ ” having a meaning automatically rises relatively. In contrast, a subject with aphasia is incapable of recognizing such characters as a sequence of characters having a meaning and tends to view another region or view the entire screen randomly with no rise in the % fixation duration for which such portion is focused on. 
     As described above, cognitive impairment diagnostic device  1  that performs the second diagnostic process includes: obtainer  41  that obtains a distribution map representing a distribution of gaze points of a subject on a movie for cognitive assessment; and diagnoser  39  that makes diagnosis of cognitive impairment, based on the distribution map. Here, the movie for cognitive assessment includes: a first region including a correct image for cognitive assessment or an image for encoding; and a plurality of second regions including other images. Diagnoser  39  calculates, in the distribution map on the movie for cognitive assessment, a percentage of fixation duration for which the first region is focused on or a percentage of fixation duration for which at least one of the plurality of second regions is focused on, and makes diagnosis of whether cognitive impairment is present by comparing the percentage of fixation duration with a threshold. 
     Also, cognitive impairment diagnostic device  1  that performs the second diagnostic process includes: display  10  including a display surface; imager  21  that captures an image of the eyes of a subject; detector  37  that detects, on the time series, gaze points of the subject on the display surface, on the basis of the image captured by imager  21 ; a generator that generates a distribution map representing a distribution of the gaze points detected by detector  37 ; and diagnoser  39  that makes diagnosis of cognitive impairment, on the basis of the distribution map. Here, diagnoser  39  causes display  10  to display a movie for cognitive assessment that includes a first region including a correct image for cognitive assessment or an image for encoding, and a plurality of second regions including other images. Then, diagnoser  39  calculates, in the distribution map on the movie for cognitive assessment, the percentage of fixation duration for which the first region is focused on or the percentage of fixation duration for which at least one of the second regions is focused on, and makes diagnosis of the presence or absence of cognitive impairment by comparing the percentage of fixation duration with a threshold. 
     With this, it is possible to provide a cognitive impairment diagnostic device capable of making a simple, low-cost, objective, quantitative, and versatile diagnosis of cognitive impairment. It is further possible to diagnose cognitive impairment within a mere few seconds to a few tens of second. 
     Also, cognitive impairment diagnostic device  1  that performs the second diagnostic process includes: obtainer  41  that obtains a distribution map representing a distribution of gaze points of a subject on a movie for cognitive assessment; and diagnoser  39  that makes diagnosis of cognitive impairment, based on the distribution map. Here, the movie for cognitive assessment includes: the first region including a correct character image; and the plurality of second regions including incorrect character images. Diagnoser  39  calculates, in the distribution map on the movie for cognitive assessment, the percentage of fixation duration for which the first region is focused on, and makes diagnosis of suspected aphasia when the percentage of fixation duration is lower than the threshold. 
     Also, cognitive impairment diagnostic device  1  that performs the second diagnostic process includes: display  10  including a display surface; imager  21  that captures an image of the eyes of a subject; detector  37  that detects, on the time series, gaze points of the subject on the display surface, on the basis of the image captured by imager  21 ; a generator that generates a distribution map representing a distribution of the gaze points detected by detector  37 ; and diagnoser  39  that makes diagnosis of cognitive impairment, on the basis of the distribution map. Here, diagnoser  39  causes display  10  to display a movie for cognitive assessment that includes a first region including correct characters and a plurality of second regions including incorrect characters. Then, diagnoser  39  calculates, in the distribution map on the movie for cognitive assessment, the percentage of fixation duration for which the first region is focused on, and makes diagnosis of suspected aphasia when the percentage of fixation duration is lower than a threshold. 
     With this, it is possible to provide a cognitive impairment diagnostic device capable of making a simple, low-cost, objective, quantitative, and versatile diagnosis of aphasia among cognitive impairments. It is further possible to diagnose cognitive impairment within a mere few seconds to a few tens of second. 
     Here, the movie for cognitive assessment may include: an image region including an image representing an object that is known; a question region including a question sentence asking a name of the object; the first region that is a correct region including character image indicating the name of the object; and the plurality of second regions that are incorrect regions including character images other than the name of the object. 
     With this, it is possible to make diagnosis of aphasia relating to the name of an object, using a question sentence as a linguistic instruction. 
     Here, the movie for cognitive assessment may include: the correct region including characters having a meaning; and incorrect regions including characters having no meaning. With this, it is possible to make diagnosis of aphasia without using an instruction sentence and a voice instruction. 
     Here, the movie for cognitive assessment may include a plurality of characters arranged in matrix, the correct region may correspond to a row or a column that is formed of the characters having the meaning, and the incorrect regions may correspond to rows or columns formed of the characters having no meaning. 
     With this, it is possible to make diagnosis of aphasia, using a simplified movie for cognitive assessment, without using an instruction sentence and a voice instruction. 
     The cognitive impairment diagnostic program that performs the second diagnostic process is a cognitive impairment diagnostic program executed by a computer that obtains a distribution map representing a distribution of gaze points of a subject on a movie for cognitive assessment and makes diagnosis of cognitive impairment on the basis of the distribution map. Here, the movie for cognitive assessment includes a first region including a correct image for cognitive assessment or an image for encoding, and a plurality of second regions including other images. Such cognitive impairment diagnostic program causes the computer to execute: calculating, in the distribution map on the movie for cognitive assessment, the percentage of fixation duration for which the first region is focused on or the percentage of fixation duration for which at least one of the second regions is focused on; and making diagnosis of the presence or absence of cognitive impairment by comparing the percentage of fixation duration with a threshold. 
     Also, the cognitive impairment diagnostic program that performs the second diagnostic process is a cognitive impairment diagnostic program executed by a computer that includes: display  10  including a display surface; imager  21  that captures an image of the eyes of a subject; detector  37  that detects, on the time series, gaze points of the subject on the display surface, on the basis of the image captured by imager  21 ; a generator that generates a distribution map representing a distribution of the gaze points detected by detector  37 ; and diagnoser  39  that makes diagnosis of cognitive impairment, on the basis of the distribution map. Such cognitive impairment diagnostic program causes the computer to execute: causing display  10  to display a movie for cognitive assessment that includes a first region including a correct image for cognitive assessment or an image for encoding, and a plurality of second regions including other images; calculating, in the distribution map on the movie for cognitive assessment, the percentage of fixation duration for which the first region is focused on or the percentage of fixation duration for which at least one of the second regions is focused on; and making diagnosis of the presence or absence of cognitive impairment by comparing the percentage of fixation duration with a threshold. 
     The cognitive impairment diagnostic program that performs the second diagnostic process is a cognitive impairment diagnostic program executed by a computer that obtains a distribution map representing a distribution of gaze points of a subject on a movie for cognitive assessment and makes diagnosis of cognitive impairment on the basis of the distribution map. Here, the movie for cognitive assessment includes a first region including correct characters and a plurality of second regions including incorrect characters. Such cognitive impairment diagnostic program causes the computer to execute: calculating, in the distribution map on the movie for cognitive assessment, the percentage of fixation duration for which the first region is focused on, and making diagnosis of suspected aphasia when the percentage of fixation duration is lower than a threshold. 
     Also, the cognitive impairment diagnostic program that performs the second diagnostic process is a cognitive impairment diagnostic program executed by a computer that includes: display  10  including a display surface; imager  21  that captures an image of the eyes of a subject; detector  37  that detects, on the time series, gaze points of the subject on the display surface, on the basis of the image captured by imager  21 ; a generator that generates a distribution map representing a distribution of the gaze points detected by detector  37 ; and diagnoser  39  that makes diagnosis of cognitive impairment, on the basis of the distribution map. Such cognitive impairment diagnostic program causes the computer to execute: causing display  10  to display a movie for cognitive assessment that includes a first region including correct characters and a plurality of second regions including incorrect characters; calculating, in the distribution map on the movie for cognitive assessment, the percentage of fixation duration for which the first region is focused on; and making diagnosis of suspected aphasia when the percentage of fixation duration is lower than a threshold. 
     2.3 Third Diagnostic Process 
     Next, the third diagnostic process in step S 30  shown in  FIG.  5    will be described. The third diagnostic process uses the foregoing third characteristics to make diagnosis of cognitive impairment. 
       FIG.  23    is a flowchart of an example third diagnostic process according to the embodiment.  FIG.  24    is a diagram showing an example movie for cognitive assessment used in the third diagnostic process shown in  FIG.  23   . 
     In  FIG.  23   , PC  30  starts the detection of gaze points by detector  37  (S 201 ), displays the movie for cognitive assessment on display surface  11  (S 202 ), and calculates % fixation duration Va for which an incorrect region is focused on in the movie for cognitive assessment (S 203 ). 
     The movie for cognitive assessment here is a movie that includes a first region including a correct image and a plurality of second regions including incorrect images. The movie for cognitive assessment is, for example, a movie that includes: a first region including a correct image that represents a first graphic; an instruction sentence region that includes an instruction sentence for inducing a subject to directly focus on the first graphic; second regions including incorrect images that represent graphics similar to the first graphic; and another second region including an incorrect image that represents a graphic not similar to the first graphic. 
     An example of  FIG.  24    shows movie for cognitive assessment  a   1  that is displayed on display surface  11  for a subject. Such movie for cognitive assessment  a   1  includes an instruction sentence that reads “Focus on the hexagon”, around which the graphics of a pentagon, a hexagon, a heptagon, and a triangle are included. 
       FIG.  25    is a diagram showing an example assessment movie used in the third diagnostic process shown in  FIG.  23   . An example of  FIG.  25    shows movie for cognitive assessment  a   1  serving as the assessment movie to be displayed on display  35  of PC  30 . Movie for cognitive assessment  a   1  in  FIG.  25    includes: a first region including correct image  a   11  showing the hexagon as the first graphic; instruction sentence region  a   12  that reads “Focus on the hexagon”; and a plurality of second regions including incorrect images. The plurality of second regions include: a second region including an incorrect image showing the pentagon that is similar to the first graphic; a second region including an incorrect image showing the heptagon that is similar to the first graphic; and a second region including irrelevant incorrect image  a   13  showing the triangle that is not similar to the first graphic. 
     Further, PC  30  calculates % fixation duration Va for which incorrect regions that include incorrect images are focused on after displaying the movie for cognitive assessment (S 203 ). Here, % fixation duration Va may be the percentage (%) of the presence of gaze points in the second region in the distribution pattern of gaze points on the movie for cognitive assessment. Also, an incorrect region for which % fixation duration Va is calculated may be any one of the second region including irrelevant incorrect image  a   13 , instruction sentence region  a   12 , or a region including a combination of the second region of irrelevant incorrect image  a   13  and instruction sentence region  a   12 . 
     Next, PC  30  determines whether % fixation duration Va calculated is greater than threshold th5 (S 204 ). When determining that % fixation duration Va is greater than threshold th5, the subject is diagnosed as having cognitive impairment (S 205 ). 
     PC  30  further determines whether % fixation duration Va calculated is lower than threshold th5 and greater than threshold th6 (S 206 ). When determining that % fixation duration Va is lower than threshold th5 and greater than threshold th6, the subject is diagnosed as having suspected cognitive impairment (S 207 ). 
     PC  30  further determines whether % fixation duration Va calculated is lower than threshold th6 (S 208 ). When determining that % fixation duration Va is lower than threshold th6, the subject is diagnosed as having no cognitive impairment (S 209 ). 
     Threshold th5 and threshold th6 can be appropriately set by calculating % fixation duration Va of a plurality of subjects who are known beforehand whether having or not having cognitive impairment. 
     Note that the flowchart of  FIG.  23    may include, instead of steps S 201  and S 202 , a step of obtaining a distribution map that represents the distribution of gaze points of a subject on the movie for cognitive assessment. The flowchart in which such steps are replaced by the step of obtaining the distribution map is easily implemented by PC  30  shown in  FIG.  1 B  or may be implemented by PC  30  shown in  FIG.  1 A . 
       FIG.  26    is a diagram showing an example distribution map in the third diagnostic process that is performed, using  FIG.  24   , on a subject without cognitive impairment. As shown in the diagram, the subject without cognitive impairment selects and focuses on correct image all from the alternatives in accordance with the instruction sentence shown on the screen. The % fixation duration for which s/he focuses on incorrect images is low. In particular, the % fixation duration for which irrelevant incorrect image  a   13  is focused on is extremely low. 
      In the third diagnostic process, the cognitive function of the subject is assessed, using as a measure, not the % fixation duration for which the correct image is focused on, but the % fixation duration for which an incorrect image is focused on and the % fixation duration for which the instruction sentence region is focused on. Stated differently, the % fixation duration for which the instruction sentence region is focused on and the % fixation duration for which incorrect images are focused on in the movie for cognitive assessment are inversely correlated with the cognitive function of the subject. It is thus possible to assess cognitive function, using these % fixation duration as a measure. 
     In particular, the % fixation duration for which “irrelevant incorrect image” is focused on is inversely correlated with the cognitive function of the subject among the % fixation duration for which incorrect images are focused on. Suppose, for example, that four alternative are presented, one of which is a correct image and other three are incorrect images. Also suppose that one of the three incorrect images that is no similar to the correct image is regarded as an irrelevant incorrect image. Stated differently, the irrelevant incorrect image is an alternative that can be determined to be clearly incorrect by a person with normal cognitive function. While the % fixation duration for which the correct image is focused on is positively correlated with the cognitive function of a subject, the % fixation duration for which the irrelevant incorrect image is focused on is negatively correlated with the cognitive function of a subject. 
     The movie for cognitive assessment in  FIG.  24    shows four images (pentagon, hexagon, heptagon, and triangle) as the alternatives as well as the instruction sentence that reads “Focus on the hexagon”. Here, the hexagon is “correct image” and the triangle is “irrelevant incorrect image” in this case. The pentagon and the heptagon are similar to the hexagon serving as the correct answer, and thus cause confusion in selecting the correct answer, but the triangle cannot be confusing for a cognitively unimpaired person. 
       FIG.  27    is a diagram showing a correlation between an MMSE score and the percentage of fixation duration for which the instruction sentence region in  FIG.  25    is focused on in the third diagnostic process.  FIG.  28    is a diagram showing a correlation between an MMSE score and the percentage of fixation duration for which the irrelevant incorrect image in  FIG.  25    is focused on in the third diagnostic process. 
     As shown in  FIG.  27    and  FIG.  28   , the % fixation duration for which instruction sentence region  a   12  is focused on and the % fixation duration for which irrelevant incorrect image  a   13  is focused on are both negatively correlated with the cognitive functioning score (MMSE score) of subjects from the standpoint of statistical significance. 
     On the basis of the above, the third diagnostic process assesses the cognitive function of a subject, using as a measure, not the % fixation duration for which the correct image is focused on, but the % fixation duration for which an incorrect image is focused on and the % fixation duration for which the instruction sentence region is focused on. 
     As described above, cognitive impairment diagnostic device  1  that performs the third diagnostic process includes: obtainer  41  that obtains a distribution map representing a distribution of gaze points of a subject on a movie for cognitive assessment; and diagnoser  39  that makes diagnosis of cognitive impairment, based on the distribution map. Here, the movie for cognitive assessment includes a first region including a correct image and a plurality of second regions including incorrect images. Diagnoser  39  calculates, in the distribution map on the movie for cognitive assessment, a percentage of fixation duration for which a region other than the first region is focused on, and makes diagnosis of suspected cognitive impairment when the percentage of fixation duration is higher than the threshold. 
     Also, cognitive impairment diagnostic device  1  that performs the third diagnostic process includes: display  10  including a display surface; imager  21  that captures an image of the eyes of a subject; detector  37  that detects, on the time series, gaze points of the subject on the display surface, on the basis of the image captured by imager  21 ; a generator that generates a distribution map representing a distribution of the gaze points detected by detector  37 ; and diagnoser  39  that makes diagnosis of cognitive impairment, on the basis of the distribution map. Here, diagnoser  39  causes display  10  to display a movie for cognitive assessment that includes a first region including a correct image and a plurality of second regions including incorrect images. Then, diagnoser  39  calculates, in the distribution map on the movie for cognitive assessment, the percentage of fixation duration for which a region other than the first region is focused on, and makes diagnosis of suspected cognitive impairment when the percentage of fixation duration is higher than a threshold. 
     With this, it is possible to provide a cognitive impairment diagnostic device capable of making a simple, low-cost, objective, quantitative, and versatile diagnosis of cognitive impairment. What is more, cognitive impairment is diagnosed, using as a measure, the percentage of fixation duration for which an incorrect image is focused on. It is further possible to diagnose cognitive impairment within a mere few seconds to a few tens of second. 
     Here, the movie for cognitive assessment may include: an instruction sentence region including an instruction sentence inducing a direct focus on a first graphic; the first region including the correct image representing the first graphic; a second region including an incorrect image representing a graphic similar to the first graphic, the second region being included in the plurality of second regions; and an other second region including an incorrect image representing a graphic not similar to the first graphic, the other second region being included in the plurality of second regions. Here, diagnoser  39  calculates a percentage of fixation duration for which the instruction sentence region or the other second region is focused on. 
     With this, it is possible to diagnose cognitive impairment, using as a measure, the % fixation duration for which the instruction sentence region or the other second region is focused on. 
     Also, the cognitive impairment diagnostic program that performs the third diagnostic process is a cognitive impairment diagnostic program executed by a computer that obtains a distribution map representing a distribution of gaze points of a subject on a movie for cognitive assessment and makes diagnosis of cognitive impairment on the basis of the distribution map. Here, the movie for cognitive assessment includes a first region including a correct image and a plurality of second regions including incorrect images. Such cognitive impairment diagnostic program causes the computer to execute: calculating, in the distribution map on the movie for cognitive assessment, the percentage of fixation duration for which a region other than the first region is focused on; and making diagnosis of suspected cognitive impairment when the percentage of fixation duration is higher than a threshold. 
     Also, the cognitive impairment diagnostic program that performs the third diagnostic process is a cognitive impairment diagnostic program executed by a computer that includes: display  10  including a display surface; imager  21  that captures an image of the eyes of a subject; detector  37  that detects, on the time series, gaze points of the subject on the display surface, on the basis of the image captured by imager  21 ; a generator that generates a distribution map representing a distribution of the gaze points detected by detector  37 ; and diagnoser  39  that makes diagnosis of cognitive impairment, on the basis of the distribution map. Such cognitive impairment diagnostic program causes the computer to execute: causing display  10  to display a movie for cognitive assessment that includes a first region including a correct image, and a plurality of second regions including incorrect images; calculating, in the distribution map on the movie for cognitive assessment, the percentage of fixation duration for which a region other than the first region is focused on; and making diagnosis of suspected cognitive impairment when the percentage of fixation duration is higher than a threshold. 
     Note that cognitive impairment diagnostic device  1  may be configured to perform processing simultaneously on a plurality of subjects. In this case, imager  21  is simply required to capture images of a plurality of subjects, detector  37  is simply required to detect gaze points of each of the subjects, generator  38  is simply required to generate a distribution map for each of the subjects, and diagnoser  39  is simply required to make diagnosis on each of the subjects. When configured to perform processing simultaneously on a plurality of subjects, cognitive impairment diagnostic device  1  may include a plurality of imaging devices  20 . In this case, one imaging device  20  may be used for one subject or for a plurality of subjects. This enables cognitive impairment diagnostic device  1  to further increase the efficiency in a mass medical examination. 
     Note that the foregoing embodiment and variation thereof are intended to illustrate the technology according to the present invention, and therefore do not limit the scope of the appended Claims. The scope of the appended Claims according to the present invention thus includes modification, replacement, addition, and omission made thereto that can be conceived by those skilled in the art within the scope of the specification, the drawings, and the appended Claims or their equivalents. 
     Industrial Applicability 
     The present invention is applicable for use as a cognitive impairment diagnostic device and a cognitive impairment diagnostic program for diagnosis of cognitive impairment. 
     REFERENCE SIGNS LIST 
     
         
           1  cognitive impairment diagnostic device 
           10  display 
           11  display surface 
           20  imaging device 
           21  imager 
           22 ,  23  camera 
           24  light source unit 
           25 ,  26  light source 
           30  PC 
           31  processor 
           32  storage 
           33  inputter 
           34  outputter 
           35  display 
           36  interface 
           37  detector 
           38  generator 
           39  diagnoser 
           300  movie data for cognitive assessment 
           301  first movie data 
           302  second movie data 
           303  third movie data 
           310  case characteristics data 
           311  first characteristics data 
           312  second characteristics data 
           313  third characteristics data 
           320  program 
           321  cognitive impairment diagnostic program 
           322  gaze point data 
           323  distribution map data 
           324  database