Head posture change analysis system

Abstract

Provided is a head posture change analysis system for analyzing whether a head posture of a subject is acting appropriately or not. The present invention includes a measuring means for measuring a head posture of a subject at predetermined time intervals, and an analyzing means for analyzing the measurement data and generating waveform data indicating change in angular velocity of the head posture. The analyzing means determines whether or not the waveform data, generated on the basis of the measurement data generated within a target period including a first timing at which the angular velocity of the head posture of the subject exceeds a first threshold value, is valid.

Description

Head position change analysis system

[0001] The present invention relates to a head position change analysis system.

[0002] One type of test for dizziness is the Video Head Impulse Test (vHIT). A test involves having a subject wear examination goggles (equipped with equipment to measure gaze position and head position), and a doctor or other medical professional measures eye movement as the subject rapidly moves their head. The results are then analyzed to determine whether or not there is a disorder in the left and right semicircular canals, which is one of the causes of dizziness.

[0003] Patent Document 1 discloses an invention relating to a device for assisting balance training using a head-mounted display capable of displaying virtual reality images. This invention can induce dizziness in a user by playing virtual reality images that induce visually induced dizziness on the head-mounted display and controlling the playback speed. Patent Document 1 also discloses the above-mentioned video head impulse test.

[0004] JP 2024-39250 A

[0005] When conducting a video head impulse test, medical professionals must rapidly move the subject's head position multiple times, but this is not always possible, and if the head position cannot be moved appropriately, the measurement data required for the test cannot be obtained.

[0006] In view of the above-mentioned problems, the present invention can provide a head position change analysis system that analyzes whether the head position of a subject is moving appropriately.

[0007] According to the present invention, there is provided a head position change analysis system comprising: a measurement means for measuring the head position of a subject at predetermined time intervals; and an analysis means for analyzing the measurement data generated by the measurement means to generate waveform data representing changes in the angular velocity of the head position, wherein the analysis means determines whether the generated waveform data is valid based on the measurement data generated within a target period including a first timing at which the angular velocity of the head position of the subject exceeds a first threshold.

[0008] According to the above invention, it is possible to determine whether a change in head position is valid or not based on measurement data generated within the period to be analyzed (the period to be analyzed including the first timing at which the angular velocity of the subject's head position exceeds the first threshold).

[0009] According to the present invention, there is provided a head position change analysis system for analyzing whether or not the head position of a subject is moving appropriately.

[0010] FIG. 1 is a configuration diagram of an analysis system according to the present invention. FIG. 2 is a flowchart showing a processing procedure for head position analysis according to the present invention. FIG. 3 is a diagram showing a display screen of a display means at a timing when it is determined that a waveform is successful in lateral mode. FIG. 4 is a diagram showing a display screen of a display means at a timing when it is determined that a waveform is not successful in lateral mode. FIG. 5 is a diagram showing a display screen of a display means at a timing when it is determined that a waveform is successful in LARP mode. FIG. 6 is a diagram showing a display screen of a display means at a timing when it is determined that a waveform is not successful in LARP mode.

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same components are denoted by the same reference numerals, and the description thereof will be omitted where appropriate.

[0012] <Configuration of analysis system 100 according to the present invention> First, the configuration of analysis system 100 according to the present invention will be described. Analysis system 100 is a system that analyzes head position changes of a subject. In this embodiment, the present invention will be described with respect to a configuration that analyzes head position changes of a subject, assuming that a video head impulse test is performed. However, the present invention is not necessarily limited to video head impulse tests, and can also be applied to other tests.

[0013] FIG. 1 is a configuration diagram of an analysis system 100 according to the present invention. As shown in FIG. 1, the analysis system 100 includes a head-mounted device 110 and a computer terminal 120, which are communicatively connected to each other. The head-mounted device 110 can transmit measured data (data showing changes in the subject's gaze and head position over time) to the computer terminal 120. In implementing the present invention, communication between the head-mounted device 110 and the computer terminal 120 may be wireless or wired, and they may be directly connected to each other or indirectly connected via another device (not shown). Each of the head-mounted device 110 and the computer terminal 120 includes an information processing device such as a CPU (not shown) and a storage device such as a ROM or RAM (not shown). The hardware and installed software work together to execute the various processes described below.

[0014] The head-mounted device 110 is a pair of test goggles worn on the head of the test subject, and includes a gaze measurement unit 111, a head position measurement unit 112, and an eye image capture unit 113. The gaze measurement unit 111 measures the gaze of the test subject at predetermined time intervals during the video head impulse test. The gaze measurement unit 111 can be implemented by an eye tracker (a sensor that detects the test subject's gaze). The gaze of the test subject measured by the gaze measurement unit 111 includes the rotation axis and angle of the test subject's eyeball, and the position of the test subject's gaze (the position at which the test subject is gazing). The head position measurement unit 112 measures the head position of the test subject at predetermined time intervals during the video head impulse test, and corresponds to the measurement unit of the present invention. The head position measurement unit 112 can be implemented by a gyro sensor (a sensor that detects angular velocity) or the like. Because head position changes rapidly during a video head impulse test, it is preferable that the measurement time interval by the head position measuring means 112 be very short, and in this embodiment it is set to 120 fps (120 measurements per second). The eyeball imaging means 113 images the subject's eyes during the video head impulse test. The eyeball imaging means 113 can be realized by a camera or the like.

[0015] In carrying out the present invention, the component corresponding to the measuring means (in this embodiment, the head position measuring means 112) does not necessarily have to be attached to the head of the subject, but can also be attached to another part of the body or can be measured externally without contact.

[0016] The computer terminal 120 processes the measurement data measured by the head-mounted device 110 and includes an analysis unit 121 and a display unit 122. The analysis unit 121 can analyze the measurement data measured by the head-mounted device 110 and corresponds to the analysis unit of the present invention. The analysis results of the analysis unit 121 include (1) eye movement waveforms (waveform data representing changes in the position of the subject's gaze), (2) head position angular velocity (peak value of the angular velocity of the subject's head position), (3) head position sway amplitude (angle of the subject's front direction swaying left and right or forward and backward), and (4) head position waveforms (waveform data representing changes in the angular velocity of the subject's head position). The analysis unit 121 can be realized by executing application software installed on the computer terminal 120. The display unit 122 displays the results of the analysis by the analysis unit 121. The display format of the display unit 122 will be described later. In carrying out the present invention, the output of the analysis results by the analysis means 121 does not necessarily have to be a display output, but may be replaced with other forms of output such as a printed output.

[0017] <Head position analysis flow according to the present invention> Next, the head position analysis flow according to the present invention will be described. Fig. 2 is a flowchart showing the processing procedure of head position analysis according to the present invention.

[0018] First, the computer terminal 120 acquires the measurement data measured by the head-mounted device 110 (step S101). In the process of step S101, the computer terminal 120 may acquire the measurement data directly from the head-mounted device 110, or may acquire the measurement data by reading out the measurement data stored in a storage device (not shown).

[0019] Since the head position waveform included in the measurement data acquired in step S101 contains a large amount of noise, it is necessary to reduce the influence of noise in order for the computer terminal 120 to analyze nystagmus with high accuracy. Therefore, in order to reduce the influence of noise, the computer terminal 120 smoothes the head position waveform acquired in step S101 (step S102). The smoothing method performed in step S102 is not particularly limited and may be selected appropriately from known methods.

[0020] Next, the computer terminal 120 analyzes the head position waveform (waveform data representing changes in the angular velocity of the subject's head position) to determine the start point (step S103). Here, the "start point" refers to the point at which the angular velocity of the subject's head position exceeds A degrees / second (the first threshold value according to the present invention). This corresponds to the first timing according to the present invention. If the computer terminal 120 does not detect the start point in the processing of step S103 (NO in step S104), it returns to the processing of step S103. If the computer terminal 120 detects the start point in the processing of step S103 (YES in step S104), it refers to the measurement data after the start point and determines whether the measurement data is worth analyzing (step S105). Specifically, the computer terminal 120 determines that the measurement data is worth analyzing when the state in which the angular velocity of the subject's head position is equal to or greater than A degrees / second is maintained for B seconds or more from the start point. Note that the angular velocity equivalent to A degrees / second and the time equivalent to B seconds described above can be changed as appropriate within the scope of achieving the objectives of the present invention.

[0021] If the measurement data is not worthy of analysis (NO in step S105), the process returns to step S103. If the measurement data is deemed worthy of analysis (YES in step S105), the computer terminal 120 determines whether the waveform data generated based on the measurement data generated within the target period including the start point is valid (step S106). Here, the "target period" is a finite period determined based on the start point, and in this embodiment, it is 0.7 seconds, including C seconds before the start point (corresponding to the first period according to the present invention) and D seconds after the start point (corresponding to the second period according to the present invention). Note that the time corresponding to C seconds and D seconds can be changed as appropriate within the scope of achieving the objectives of the present invention. In the following description, waveform data determined to be valid in step S106 is referred to as a successful waveform.

[0022] The conditions under which the computer terminal 120 determines a waveform as successful in step S106 are as follows. Note that in implementing the present invention, it is not necessary to use all of the conditions; some may be omitted or replaced with other conditions. Furthermore, the numerical values ​​of each condition mentioned below may be changed as appropriate within the scope of achieving the object of the present invention.

[0023] In step S106, the computer terminal 120 determines that a waveform is successful if the number of measurement data points generated during a period (corresponding to a third period according to the present invention) beginning at the start point and ending when the angular velocity of the subject's head position falls below E degrees / second (the second threshold according to the present invention) is F frames / second or more (the third threshold according to the present invention), and determines that a waveform is not successful if the number of measurement data points generated during the period is less than F frames / second. Also, in step S106, the computer terminal 120 determines that a waveform is successful if the length of the period is G seconds (the fourth threshold according to the present invention) or less, and determines that a waveform is not successful if the length of the period is more than G seconds. Note that the time corresponding to E seconds, the number of points corresponding to F frames / second, and the time corresponding to G seconds can be changed as appropriate within the scope of achieving the objectives of the present invention.

[0024] In step S106, the computer terminal 120 determines that all of the angular velocities of the subject's head position analyzed from the measurement data generated during a period (corresponding to a fourth period according to the present invention) starting from the beginning of the initial part of the target period (the first period according to the present invention) and ending before the starting point are equal to or less than A degrees / second (the first threshold according to the present invention), and determines that the waveform is not successful if any of the angular velocities of the subject's head position analyzed from the measurement data generated during that period exceed A degrees / second. Also, in step S106, the computer terminal 120 determines that all of the angular velocities of the subject's head position analyzed from the measurement data generated during a period (corresponding to a fifth period according to the present invention) ending at the end of the final part of the target period (the second period according to the present invention) are equal to or less than A degrees / second (the first threshold according to the present invention), and determines that the waveform is not successful if any of the angular velocities of the subject's head position analyzed from the measurement data generated during that period exceed A degrees / second.

[0025] In step S106, the computer terminal 120 determines that the waveform is a success when all of the subject's head position angles analyzed from the measurement data generated during the target period are equal to or greater than the subject's head position angles analyzed from the measurement data generated at the start point (i.e., when the head position angle has not returned from the start position of the head swing). Also, in step S106, the computer terminal 120 determines that the waveform is not a success when any of the subject's head position angles analyzed from the measurement data generated during the target period is lower than the subject's head position angles analyzed from the measurement data generated at the start point (i.e., when the head position angle has returned from the start position of the head swing).

[0026] In step S106, the computer terminal 120 determines that the waveform is successful when all of the angles of the subject's head position analyzed from the measurement data generated during the target period are within the specified range. Furthermore, in step S106, the computer terminal 120 determines that the waveform is not successful when any of the angles of the subject's head position analyzed from the measurement data generated during the target period are outside the specified range. Here, the "specified range" refers to the range of head swing angles arbitrarily specified by the user (e.g., a medical professional) before conducting a video head impulse test.

[0027] In step S106, the computer terminal 120 detects the peak point (corresponding to the third timing in the present invention) where the angular velocity of the subject's head position is at its maximum; the start point of the peak (corresponding to the fourth timing in the present invention) where the angular velocity of the subject's head position first falls below 20 degrees / second (the fourth threshold in the present invention) by sequentially referencing the measurement data on the front side of the peak point; and the end point of the peak (corresponding to the fifth timing in the present invention) where the angular velocity of the subject's head position first falls below 0 degrees / second (the fifth threshold in the present invention) by sequentially referencing the measurement data on the back side of the peak point. For each of the measurement data generated from the start point of the peak to the end point of the peak, extreme data where the product of the front and rear slopes is negative is detected. The computer terminal 120 then determines a waveform as successful if the angular velocity at the peak point is within a specified range, and determines a waveform as not successful if the angular velocity at the peak point is outside the specified range. Here, the "specified range" refers to a range of angular velocities arbitrarily specified by the user prior to the video head impulse test. Furthermore, the computer terminal 120 determines a waveform as successful when the difference in head position angle from the start point to the peak point is within a specified range, and determines a waveform as not successful when the difference in head position angle from the start point to the peak point is outside the specified range. Here, the "specified range" refers to the range of angle difference from the start point to the peak point that the user arbitrarily specifies before conducting the video head impulse test. Furthermore, the computer terminal 120 determines a waveform as successful when the peak point contains only extreme value data with a positive leading slope and a negative trailing slope, and determines a waveform as not successful when extreme value data with a positive leading slope and a negative trailing slope is present in data other than the measurement data at the third timing. Furthermore, the computer terminal 120 determines a waveform as not successful when there are multiple extreme value data with a negative leading slope and a positive trailing slope. Furthermore, when there is one extreme value data with a negative leading slope and a positive trailing slope, the computer terminal 120 determines that the waveform is a successful waveform if the value obtained by multiplying the larger of the preceding and following slopes of the extreme value data by a predetermined value is greater than the smaller of the preceding and following slopes, and determines that the waveform is not a successful waveform if the value obtained by multiplying the larger of the preceding and following slopes of the extreme value data by a predetermined value (0.3 in this embodiment) is equal to or less than the smaller of the preceding and following slopes.Alternatively, if the value obtained by dividing the larger of the slopes before and after the extreme value data by the smaller of the larger of the slopes before and after the extreme value data is greater than a predetermined value, the waveform is determined to be successful, and if the value obtained by dividing the larger of the slopes before and after the extreme value data by the smaller of the larger of the slopes before and after the extreme value data is equal to or less than the predetermined value, the waveform is determined not to be successful. Note that the predetermined value here is a value greater than 0 and less than 1, and is determined in advance.

[0028] When the computer terminal 120 determines that the waveform is a successful waveform in the processing of step S106 (YES in step S107), it displays the successful waveform on the display means 122 (step S108). When the computer terminal 120 determines that the waveform is not a successful waveform in the processing of step S106 (NO in step S107), it displays the reason why the waveform was not determined to be a successful waveform (cause of an error) on the display means 122 (step S109).

[0029] When the analysis of the measurement data acquired in step S101 has not been completed (NO in step S110), the computer terminal 120 returns to the process of step S103. When the analysis of all the measurement data acquired in step S101 has been completed (YES in step S110), the computer terminal 120 ends the head position analysis process.

[0030] <Display Mode of Head Position Analysis Results> Next, the display mode of the analysis results of the head position analysis described above will be explained. Figures 3 to 6 are diagrams showing the screen of the display means 122 that displays the analysis results of the head position analysis. As shown in each of these figures, this screen is mainly divided into a display area A1 for waveform data, a display area A2 for successful waveforms, a display area A3 for eyeball images, and a display area A4 for the control panel.

[0031] Display area A1 is used to display the eye movement waveform measured by the gaze measurement means 111 and the head position waveform measured by the head position measurement means 112. Waveform data that changes over time scrolls from right to left in display area A1 (from top to bottom in Figures 3 to 6). Note that, because the eye movement waveform is not necessary for explaining the present invention, only the head position waveform is illustrated in this specification, and the eye movement waveform is not illustrated. Display area A2 displays the successful waveform when the analysis means 121 determines that the waveform is successful. This display corresponds to the processing of step S108 in Figure 2. Display area A3 can display an image of the eyeball captured by the eyeball imaging means 113, but the specific image content is not illustrated because it is not necessary for explaining the present invention. Display area A4 displays the cause of the error that led to the determination when the analysis means 121 determines that the waveform is not successful. This display corresponds to the processing of step S109 in Figure 2. The display area A4 can also display the direction in which the subject's head is currently facing, the type of test mode currently being performed, and the number of times a successful waveform has been identified in that test mode.

[0032] FIG. 3 is a diagram showing the display screen of the display means 122 at the timing when a successful waveform is determined in lateral mode. Specifically, in FIG. 3, the mountain-shaped waveform displayed in the center of the display area A1 is determined to be a successful waveform. FIG. 4 is a diagram showing the display screen of the display means 122 at the timing when a non-successful waveform is determined in lateral mode. In FIG. 4, the mountain-shaped waveform displayed in the center of the display area A1 is determined to be a non-successful waveform. Here, lateral refers to a test that tests lateral semicircular canal function in a video head impulse test. In lateral mode, the practitioner rapidly moves the subject's head from side to side.

[0033] As shown in Fig. 3, when the analysis means 121 determines that the waveform is a success, the display means 122 displays the success waveform in display area A2. Also, as shown in Fig. 4, when the analysis means 121 determines that the waveform is not a success, the display means 122 displays the cause of the error in the determination in display area A4. Note that in this figure, it is displayed that the causes of the error are that the angular velocity at the peak point was faster than a specified range, that the difference in head position angle from the start point to the peak point was larger than a specified range, and that the length of the target period was long.

[0034] FIG. 5 illustrates the display screen of the display unit 122 at the timing when a successful waveform is determined in LARP mode. Specifically, in FIG. 5, the peak-shaped waveform displayed in the center of the display area A1 is determined to be a successful waveform. FIG. 6 illustrates the display screen of the display unit 122 at the timing when a non-successful waveform is determined in LARP mode. In FIG. 6, the peak-shaped waveform displayed in the center of the display area A1 is determined to be a non-successful waveform. Here, LARP stands for Left Anterior-Right Posterior, and is a test that evaluates the function of the left anterior and right posterior semicircular canals. In LARP mode, the subject's head is rotated 45 degrees horizontally to the right from a position facing forward in a video head impulse test, i.e., with the subject's left cheek facing forward, the practitioner rapidly moves the subject's head back and forth.

[0035] As shown in Fig. 5, when it is determined that the waveform is a success, the display means 122 displays the success waveform in display area A2. Also, as shown in Fig. 6, when it is determined that the waveform is not a success, the display means 122 displays the cause of the error in the determination in display area A4. Note that this figure displays that the cause of the error is that the difference in head position angle from the start point to the peak point was larger than the specified range, and that the subject's head position angle during the target period contained an invalid value.

[0036] As described above, by using the analysis system 100 according to this embodiment, the practitioner of the video head impulse test can visually perform the video head impulse test, making the test easier to perform.

[0037] <Modifications> The above-described embodiment of the present invention can be modified in various ways within the scope of achieving the object of the present invention.

[0038] The system configuration shown in FIG. 1 is merely one specific example of the configuration of the present invention, and some components may be omitted or other components may be added within the scope of achieving the object of the present invention.

[0039] The processing procedure shown in FIG. 2 is merely one specific example of the processing procedure according to the present invention, and some processing may be omitted, other processing may be added, the order of the processing procedure may be changed, or one processing may be executed in parallel with another processing, within the scope of achieving the object of the present invention.

[0040] The display modes shown in Figures 3 to 6 are merely specific examples of output modes of analysis results according to the present invention, and the layout of each display area and the content of each display can be changed as appropriate within the scope of achieving the object of the present invention.

[0041] This embodiment encompasses the following technical concepts: (1) A head position change analysis system comprising: a measurement means for measuring the head position of a subject at predetermined time intervals; and an analysis means for analyzing the measurement data generated by the measurement means to generate waveform data representing changes in the angular velocity of the head position, wherein the analysis means determines whether the waveform data generated based on the measurement data generated within a target period including a first timing at which the angular velocity of the head position of the subject exceeds a first threshold. (2) The head position change analysis system described in (1), wherein the target period includes a first period before the first timing and a second period after the first timing. (3) The head position change analysis system described in (2), wherein the analysis means determines the waveform data as valid when the number of points of the measurement data generated during a third period starting from the first timing and ending at a second timing at which the angular velocity of the head position of the subject falls below a second threshold is equal to or greater than a third threshold, and determines the waveform data as invalid when the number of points of the measurement data generated during the third period is below the third threshold. (4) The head position change analysis system according to (2), wherein the analysis means validates the waveform data when a time length of a third period, which starts at the first timing and ends at a second timing at which the angular velocity of the head position of the subject falls below a second threshold, is equal to or less than a fourth threshold, and invalidates the waveform data when the time length of the third period exceeds the fourth threshold. (5) The head position change analysis system according to (2), wherein the analysis means validates the waveform data when all angular velocities of the head position of the subject analyzed from the measurement data generated during a fourth period, which starts at the beginning of the first period and ends at a time before the first timing, are equal to or less than the first threshold, and invalidates the waveform data when any angular velocities of the head position of the subject analyzed from the measurement data generated during the fourth period exceed the first threshold.(6) The head position change analysis system according to (2), wherein the analysis means validates the waveform data when all angular velocities of the head position of the subject analyzed from the measurement data generated during a fifth period, which has a starting point after the first timing and an end point at the end of the second period, are equal to or less than the first threshold, and invalidates the waveform data when any angular velocities of the head position of the subject analyzed from the measurement data generated during the fifth period exceed the first threshold. (7) The head position change analysis system according to (2), wherein the analysis means validates the waveform data when all angles of the head position of the subject analyzed from the measurement data generated during the target period are equal to or greater than the angle of the head position of the subject analyzed from the measurement data generated at the first timing, and invalidates the waveform data when any angle of the head position of the subject analyzed from the measurement data generated during the target period is less than the angle of the head position of the subject analyzed from the measurement data generated at the first timing. (8) The head position change analysis system described in (2), wherein the analysis means validates the waveform data when all of the angles of the subject's head position analyzed from the measurement data generated during the target period are within a specified range, and invalidates the waveform data when any of the angles of the subject's head position analyzed from the measurement data generated during the target period are outside the specified range.(9) The analysis means detects from the target period a third timing at which the angular velocity of the head position of the subject is at its maximum, a fourth timing at which the angular velocity of the head position of the subject first falls below a fourth threshold value by sequentially referring to the measurement data on the front side with respect to the third timing as a reference, and a fifth timing at which the angular velocity of the head position of the subject first falls below a fifth threshold value by sequentially referring to the measurement data on the back side with respect to the third timing as a reference, and detects extreme value data where the product of the front and back slopes is negative for each of the measurement data generated from the fourth timing to the fifth timing, and determines the waveform data to be valid when the extreme value data where the front slope is positive and the back slope is negative is present in the measurement data other than the measurement data on the third timing, in the head position change analysis system described in (2). (10) The head position change analysis system according to (9), wherein the analysis means determines the waveform data to be invalid when there are multiple pieces of extreme value data with a negative leading slope and a positive trailing slope.(11) The head position change analysis system according to (9), wherein the analysis means determines the waveform data to be valid when there is one piece of extreme value data with a negative leading slope and a positive trailing slope, and determines the waveform data to be invalid when a value obtained by multiplying the larger of the slopes before and after the extreme value data by a predetermined value is greater than a smaller one, and determines the waveform data to be invalid when a value obtained by multiplying the larger of the slopes before and after the extreme value data by the predetermined value is equal to or less than the smaller one, or determines the waveform data to be valid when a value obtained by dividing the larger of the slopes before and after the extreme value data by the smaller one is greater than a predetermined value, and determines the waveform data to be invalid when a value obtained by dividing the larger of the slopes before and after the extreme value data by the smaller one is equal to or less than the predetermined value.

[0042] This application claims priority based on Japanese Patent Application No. 2024-125961, filed August 1, 2024, the disclosure of which is incorporated herein in its entirety by reference.

[0043] 100 Analysis system 110 Head-mounted device 111 Gaze measurement means 112 Head position measurement means 113 Eyeball photographing means 120 Computer terminal 121 Analysis means 122 Display means

Claims

1. A head position change analysis system comprising: a measurement means for measuring the head position of a subject at predetermined time intervals; and an analysis means for analyzing the measurement data generated by said measurement means to generate waveform data representing changes in angular velocity of the head position, wherein said analysis means determines whether the waveform data generated based on the measurement data generated within a target period including a first timing at which the angular velocity of the head position of the subject exceeds a first threshold is valid.

2. The head position change analysis system according to claim 1, wherein the target period includes a first period before the first timing and a second period after the first timing.

3. The head position change analysis system according to claim 2, wherein the analysis means determines that the waveform data is valid when the number of points of the measurement data generated during a third period, which starts at the first timing and ends at the second timing at which the angular velocity of the subject's head position falls below a second threshold, is equal to or greater than a third threshold, and determines that the waveform data is invalid when the number of points of the measurement data generated during the third period is below the third threshold.

4. The head position change analysis system of claim 2, wherein the analysis means determines that the waveform data is valid when the length of a third period, which begins at the first timing and ends at the second timing at which the angular velocity of the subject's head position falls below the second threshold, is equal to or less than a fourth threshold, and determines that the waveform data is invalid when the length of the third period exceeds the fourth threshold.

5. The head position change analysis system according to claim 2, wherein the analysis means validates the waveform data when all of the angular velocities of the head position of the subject analyzed from the measurement data generated during a fourth period, which starts at the beginning of the first period and ends before the first timing, are equal to or less than the first threshold value, and invalidates the waveform data when any of the angular velocities of the head position of the subject analyzed from the measurement data generated during the fourth period exceeds the first threshold value.

6. The head position change analysis system of claim 2, wherein the analysis means validates the waveform data when all of the angular velocities of the subject's head position analyzed from the measurement data generated during a fifth period that starts after the first timing and ends at the end of the second period are equal to or less than the first threshold value, and invalidates the waveform data when any of the angular velocities of the subject's head position analyzed from the measurement data generated during the fifth period exceeds the first threshold value.

7. The head position change analysis system of claim 2, wherein the analysis means validates the waveform data when all of the angles of the subject's head position analyzed from the measurement data generated during the target period are equal to or greater than the angles of the subject's head position analyzed from the measurement data generated at the first timing, and invalidates the waveform data when any of the angles of the subject's head position analyzed from the measurement data generated during the target period is lower than the angles of the subject's head position analyzed from the measurement data generated at the first timing.

8. The head position change analysis system according to claim 2, wherein the analysis means validates the waveform data when all of the angles of the subject's head position analyzed from the measurement data generated during the target period are within a specified range, and invalidates the waveform data when any of the angles of the subject's head position analyzed from the measurement data generated during the target period are outside the specified range.

9. The head position change analysis system according to claim 2, wherein the analysis means: detects from the target period a third timing at which the angular velocity of the head position of the subject is at its maximum; a fourth timing at which the angular velocity of the head position of the subject first falls below a fourth threshold value by sequentially referring to the measurement data on the front side relative to the third timing; and a fifth timing at which the angular velocity of the head position of the subject first falls below a fifth threshold value by sequentially referring to the measurement data on the back side relative to the third timing; detects extreme value data where the product of the front and back slopes is negative for each of the measurement data generated from the fourth timing to the fifth timing; validates the waveform data when the extreme value data where the front slope is positive and the back slope is negative is only present in the measurement data at the third timing; and invalidates the waveform data when the extreme value data where the front slope is positive and the back slope is negative is present in measurement data other than the measurement data at the third timing.

10. The head position change analysis system according to claim 9, wherein said analysis means determines that said waveform data is invalid when there are a plurality of extreme value data in which the preceding gradient is negative and the following gradient is positive.

11. The head position change analysis system according to claim 9, wherein the analysis means: when there is one extreme value data in which the preceding slope is negative and the subsequent slope is positive, determines the waveform data to be valid when a value obtained by multiplying the larger of the slopes before and after the extreme value data by a predetermined value is greater than the smaller one; determines the waveform data to be invalid when a value obtained by multiplying the larger of the slopes before and after the extreme value data by the predetermined value is equal to or less than the smaller one; or determines the waveform data to be valid when a value obtained by dividing the larger of the slopes before and after the extreme value data by the smaller one is greater than a predetermined value; and determines the waveform data to be invalid when a value obtained by dividing the larger of the slopes before and after the extreme value data by the smaller one is equal to or less than the predetermined value.

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