JP5515066B2 - Flicker perception threshold measurement device, measurement method, and measurement program - Google Patents

Description

  The present invention relates to measurement of a threshold value (hereinafter, also referred to as flicker perception threshold value) in which a person starts to perceive flickering with respect to a blinking stimulus (hereinafter also referred to as flicker perception threshold value). The present invention relates to a measurement apparatus, a measurement method, and a measurement program.

  The present day is said to be a stress society, and there is a strong demand for objective measurement and evaluation methods for fatigue that can be used in daily life. Conventionally, a phenomenon in which the perception of “flicker” (flicker) when a person looks at a blinking light source changes depending on the degree of fatigue, in particular, the flicker frequency at the boundary (Critical Flicker Frequency: CFF) at which “flicker” can be perceived is fatigued. Quantitative evaluation of fatigue (flicker inspection) is performed using a phenomenon that decreases with increasing degree of fatigue. In the flicker test, the flashing frequency of the flashing light is changed (monotonically increased or decreased) over time and presented to the subject, and when the flashing changes from the invisible state to the visible state, or the flashing is visible. The frequency is measured by causing the subject to react, such as pressing a button, when there is no change. Quantitative evaluation of fatigue using flicker inspection is widely used especially in the field of industrial hygiene. However, a dedicated device equipped with an LED or the like is necessary, and no one can easily carry out it on a daily basis.

  On the other hand, the inventor of the present application makes it possible to perform a mental fatigue test based on the same flicker perception principle as the flicker test using an image presentation device with a fixed refresh rate such as a liquid crystal display and a CRT. (See Patent Document 1 below). In this technique, instead of changing the blinking frequency of the blinking light used in the conventional flicker inspection, the flicker perception is generated by changing the contrast of the blinking light. This makes it possible to easily measure mental fatigue on a daily basis using a mobile terminal device such as a mobile phone, a personal computer, or the like.

JP 2010-088862 A

  In the conventional flicker measuring apparatus, when measuring a point at which the blinking is changed from being invisible to being visible as a threshold, measurement is usually started from the same fixed starting point so that any subject can be handled. Therefore, when measuring a plurality of times (usually 5 times), there is a problem that the measurement takes a long time. This point is also the same in the method using the contrast disclosed in Patent Document 1. For example, as shown in FIG. 1, the measurement is started from a fixed frequency fs where a person can clearly not perceive blinking. At time t1 to t5, the subject perceives flickering, and the blinking frequency at that time is f1 to f5. The flicker perception threshold is obtained as an average value of the obtained measurement values f1 to f5, for example.

  In addition, in the conventional flicker test, since the perception of flicker relies only on the subject's subjective report, it cannot be determined whether the flicker was actually perceived. That is, there is a problem that it is difficult to measure an objective flicker perception threshold value. Usually, since the frequency of the flashing light is changed at a constant rate from high frequency to low frequency, after several flicker tests, the subject adjusts the timing of pressing the button and arbitrarily displays the test results. It was possible to operate. In addition, there is no clear standard for correct / incorrect answers to flicker perception, and test subjects' response timing (button press timing) tends to be arbitrary, resulting in large variations in test results. In addition, because the test subject tends to continue to see stimuli at frequencies where the flicker cannot be clearly perceived, the test time is longer and the test results may indicate less fatigue.

  Therefore, an object of the present invention is to provide a measuring apparatus, a measuring method, and a measuring program that can measure the flicker perception threshold in a shorter time than before. It is another object of the present invention to provide a measuring apparatus, a measuring method, and a measuring program capable of objectively and accurately measuring a flicker perception threshold as well as shortening the measuring time.

  The above object can be achieved by the following.

  That is, the flicker perception threshold measurement method according to the present invention is a method for measuring a flicker perception threshold of a subject by presenting the flicker stimulus to the subject, and the flicker stimulus has one of luminance difference and frequency constant. The other is a stimulus that changes, and the other is changed from the start value by changing the slope, which is the other change amount per unit time, over time, and presents a blinking stimulus. In a state where the step and the blinking stimulus are presented, the process of determining the other value as a temporary threshold when the subject perceives the flicker due to the blinking stimulus and operates the operation unit is set as a temporary measurement, and the measurement is performed a plurality of times. The value obtained by adding the provisional threshold determined in this measurement to the value obtained by multiplying the step used repeatedly, the slope used in one measurement, and the predetermined time is the value of this measurement. As the starting value for the next measurement A starting value determining step to determine, and a step of determining a flicker perception threshold of the subject using a plurality of temporary threshold values obtained by a plurality of measurements, and more than the absolute value of the slope used in one measurement A new slope with a small absolute value is used in the next measurement of this measurement.

  Preferably, when measuring the flicker perception threshold of a subject, the flicker perception threshold obtained by the previous measurement for this subject is used as the other start value in the first measurement period, and is determined when the other change is an increase. A value obtained by decreasing at a ratio of 1 may be used, and if the other change is a decrease, a value obtained by increasing at a predetermined ratio may be used.

  More preferably, one is the frequency and the other is the luminance difference, and the blinking stimulus is a stimulus generated by alternately presenting regions having two different luminances at the same position at a constant frequency, and flicker perception threshold. In this measurement method, the higher one of the two luminances is made constant, and the luminance difference is changed by changing the lower luminance.

  More preferably, the areas having two different luminances are specific areas on the two images, respectively, and the two images are divided into a plurality of areas with the same pattern, and the specific areas are randomly determined for each measurement. The operation of the operation unit by the subject is an operation of selecting one region of the plurality of regions as the specific region, and the selection by the subject in one measurement is correct. A new slope having an absolute value smaller than the absolute value of the slope used in this measurement is used in the next measurement of this measurement, and the subject in one measurement is performed. If the selection by is not correct, the start value determination step is not performed and the start value and slope used in this measurement are used in the next measurement of this measurement.

  Another method of measuring the flicker perception threshold according to the present invention is a method of measuring a flicker perception threshold of a subject by presenting the blinking stimulus to the subject, and the blinking stimulus has one of luminance difference and frequency constant. The other is a stimulus that changes, and the other is changed from the start value by changing the slope, which is the other change amount per unit time, over time, and presents a blinking stimulus. In a state where the step and the blinking stimulus are presented, the process of determining the other value as a temporary threshold when the subject perceives the flicker due to the blinking stimulus and operates the operation unit is set as a temporary measurement, and the measurement is performed a plurality of times. And the starting value reduces the flicker perception threshold obtained by measurements made on the subject prior to multiple measurements at a predetermined rate if the other change is an increase. Obtained That is the value, in the case other change is reduced is a value obtained by increasing by a predetermined ratio.

  A flicker perception threshold measuring apparatus according to the present invention includes a display unit and an operation unit for displaying a blinking stimulus to a subject, and the flickering perception threshold measurement device is one of a luminance difference and a frequency. Is a stimulus with a constant value, the other is a stimulus that changes, and the other is changed from the start value with the slope, which is the other amount of change per unit time, as the time elapses. In the displayed state, the process of determining the other value as a temporary threshold when the subject perceives flickering caused by the blinking stimulus and operates the operation unit is set as a temporary measurement, and the measurement is repeated a plurality of times. A new slope having an absolute value smaller than the absolute value of the slope used in the measurement is used in the next measurement of this measurement, and is obtained by multiplying the slope used in one measurement by a predetermined time. Determined by this measurement Provisional value obtained by adding the threshold was, as the start value for the next measurement of this measurement, using a plurality of threshold values of the provisional obtained by multiple measurements to determine the flicker perception threshold of the subject.

  A flicker perception threshold measurement program according to the present invention provides a computer or a mobile terminal device having an operation unit and a display unit with one of luminance difference and frequency set to a constant value and the other from a start value per unit time. With the function of displaying the blinking stimulus on the display unit and the blinking stimulus displayed, the subject perceives the flickering caused by the blinking stimulus. The process of determining the other value when operating the operation unit as a temporary threshold is a single measurement, multiplying the function that repeats the measurement multiple times, the slope used in the single measurement, and a predetermined time A value obtained by adding the provisional threshold value determined in this measurement to the value obtained as a starting value in the next measurement of this measurement, and a plurality of values obtained by a plurality of measurements. Using a temporary threshold of To realize a function of determining a subject's flicker perception threshold, a new slope having a smaller absolute value than the absolute value of the slope to be used in a single measurement, for use in the next measurement of this measurement.

  According to the present invention, measurement conditions (start point and slope of frequency or contrast change) are adaptively set in repeated measurement, so that the flicker perception threshold can be measured in a shorter time and more accurately than in the past. Can do. In addition to shortening the measurement time, the flicker perception threshold can be measured objectively and accurately by presenting the test subject with an image pattern that can determine correctness.

  In addition, the flicker perception threshold can be measured in a shorter time than before by setting the measurement start point according to the past measurement result of the subject.

  As a result of the experiment, the measurement time of 3 to 4 minutes in the conventional flicker inspection could be shortened to about 40 seconds by adaptively setting the measurement conditions according to the present invention.

  Thereby, anyone can easily measure mental fatigue on a daily basis, and the measurement result can be more objectively evaluated.

It is a graph which shows the change of the blink condition in the measurement of the conventional flicker perception threshold. It is a block diagram which shows the outline | summary of a structure of the measuring apparatus of the flicker perception threshold which concerns on embodiment of this invention. It is a figure which shows two images used for a flicker perception threshold value measurement. It is a graph which shows the method of changing contrast. It is a graph which shows the change of the blink condition in the measuring method of the flicker perception threshold concerning an embodiment of the invention. It is a figure which shows the time change of the image shown to a test subject. It is a flowchart which shows the control structure of the program for implement | achieving the flicker perception threshold value measuring method which concerns on embodiment of this invention. It is a graph which shows the experimental result regarding the measurement time of a flicker perception threshold. It is a graph which shows the correlation with the measured value by the measuring method of the flicker perception threshold of this invention, and the conventional flicker test value.

  In the following embodiments, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  Referring to FIG. 2, flicker perception threshold measuring apparatus 100 according to an embodiment of the present invention includes an arithmetic processing unit (hereinafter referred to as CPU) 102, a read-only memory (hereinafter referred to as ROM) 104, and rewritable. A memory (hereinafter referred to as RAM) 106, a recording unit 108, a timer 110, an interface unit (hereinafter referred to as IF unit) 112, a bus 114, a display unit 116, and an operation unit 118 are provided. The CPU 102 controls the entire measuring apparatus 100. The ROM 104 is a nonvolatile storage device, and stores a program and data for controlling the operation of the measurement device 100. The RAM 106 is a volatile storage device. The recording unit 108 is a non-volatile storage device that retains data even when power is cut off, and is, for example, a hard disk drive, a flash memory, or the like. The CPU 102 reads a program from the ROM 104 onto the RAM 106 via the bus 114, and executes the program using a part of the RAM 106 as a work area. CPU102 controls each part which comprises the measuring apparatus 100 according to a program.

  The timer 110 outputs time information using an internal clock. The IF unit 112 is an interface between the CPU 102, the display unit 116, and the operation unit 118. A CPU 102, ROM 104, RAM 106, recording unit 108, timer 110, and IF unit 112 are connected to the bus 114. Data (including control information) is exchanged between the units via the bus 114.

  The display unit 116 includes a display panel (liquid crystal panel or the like) for displaying an image and a drive unit for driving the display panel. The display unit 116 displays the image data transmitted via the IF unit 112 at a predetermined refresh rate. If the IF unit 112 and the drive unit are designed according to the format (specification) of the image signal transmitted between the IF unit 112 and the display unit 116, the image signal may be digital or analog. Good. The operation unit 118 includes keys, pads, and the like, and the subject operates the operation unit 118 to give an instruction to the measurement apparatus 100.

  As the measuring device 100, for example, a known computer or a mobile terminal device (a mobile phone, a PHS, a PDA, etc.) can be used.

  The outline of the operation of the measuring apparatus 100 will be described as follows. The CPU 102 transmits two pieces of image data to the display unit 116 via the IF unit 112 alternately at a predetermined cycle. The display unit 116 displays the received image data at a predetermined refresh rate (for example, 60 Hz) and presents it to the subject.

  The two images are multi-tone black-and-white images that include a plurality of areas partitioned by the same pattern, the specific areas of which have different luminance and the remaining areas have the same luminance. In FIG. 3, the first image 200 and the second image 210 are all divided into a plurality of regions with the same pattern (fan shape). The areas corresponding to each other have the same brightness except for the specific areas 202 and 212. For example, the specific area 202 of the first image 200 has high brightness, the specific area 212 of the second image 210 has low brightness, and the hatched fan-shaped areas 204 to 208 and 214 to 218 have the specific area 202, This is an average value of 212 luminance values. The luminance value of the background area is 0, for example. Each of the first image 200 and the second image 210 has a display unit with a cycle (1/30 = about 33.3 msec) that is twice the cycle of the refresh rate (for example, 1/60 = about 16.7 msec in the case of 60 Hz). 116. Therefore, if image data is transmitted from the CPU 102 to the display unit 116 at a predetermined timing (flashing frequency), an image in which the specific area flashes can be presented to the subject. Whether or not this blinking can be perceived depends on the blinking frequency and the luminance difference in a specific area.

  Further, the CPU 102 changes the two image data transmitted to the display unit 116 with time, and changes the luminance difference of the specific region with time in the image displayed on the display unit 116. For example, two image data in which the luminance difference ΔL between the specific areas 202 and 212 in the first image 200 and the second image 210 shown in FIG. 116.

For example, as illustrated in FIG. 4, the luminance of the specific region 212 of the second image 210 is set to the maximum luminance Lon ₀ (= Lon) while the luminance of the specific region 202 of the first image 200 is set to the maximum luminance (Lon). from to _{0, Loff 1, ···, Loff} i, ···, and Loff _n = 0, decreases at a constant rate. FIG. 4 shows a case where n gradations (for example, n = 256) are linearly changed in a period from t = 0 to T1. In FIG. 4, numbers “1” and “2” alternately attached along the time axis represent periods in which the first image 200 and the second image 210 are displayed, respectively. Since the luminance value of the specific area 202 of the first image 200 is higher than the luminance value of the specific area 212 of the second image 210, the image is displayed blinking.

FIG. 4 shows a case where the first image 200 and the second image 210 are displayed repeatedly (twice) with one luminance difference ΔL _i during T0, but when the change is abrupt. The first image 200 and the second image 210 are displayed only once with one luminance difference ΔL _i . In the case of a digital image, since the luminance is a discrete value (gradation), the luminance difference of the displayed image may not be a continuous value. In that case, the nearest integer value (gradation value) is used as the luminance value of the specific area of the second image 210. For example, when the refresh rate of the display unit 116 is 60 Hz and ΔT is about 33 ms (1/30), the same is true when the slope of the luminance change is gentler than the slope when changing one gradation in about 33 ms. The second image 210 is displayed a plurality of times. Further, when the gradient of the luminance change is steeper than the gradient when changing one gradation in about 33 ms, the gradation value representing the luminance of the specific area 212 of the second image 210 is not a continuous integer value. It becomes a jump value (there is a gradation value that is not used).

  When the subject observes the image presented on the display screen of the display unit 116 and perceives that the flickering has started or disappeared in a partial region of the image, the subject operates the operation unit 118. Specify. For example, four different keys are assigned to four areas, and the subject is made to press any key. This operation information (data) is transmitted to the CPU 102 via the IF unit 112, and the CPU 102 stores the received data in the RAM 106 or the recording unit 108. The CPU 102 determines whether the subject's operation is correct / incorrect, that is, whether the region designated by the subject is a specific region having a luminance difference in two images displayed alternately.

  If the subject cannot correctly specify the specific area, the same measurement is performed without changing the conditions (the position of the specific area, the start value of the change in luminance difference, and the slope). If the subject can correctly specify the flickering area, the next measurement is performed by changing the conditions. The position of the specific area is changed, and for example, image data in which the upper fan-shaped areas 204 and 214 in the first image 200 and the second image 210 in FIG. It is desirable to change the position of the specific area at random. Further, the luminance difference at the start of measurement of the specific area is changed, and the luminance difference is changed at a more gradual ratio.

  As described above, the measuring apparatus 100 irregularly changes the position of the specific region (region where the luminance difference is provided) of the image presented to the subject, and the subject correctly perceives the flickering ratio at which the luminance difference of the specific region is changed. It changes adaptively depending on whether it was made or not.

  With reference to FIGS. 5 to 7, the measurement of the flickering perception threshold using the measurement apparatus 100 will be described in more detail.

Referring to FIG. 5, CPU 102 linearly decreases the contrast (vertical axis) of the specific area of second image 210 in each measurement period (first period to i + 1 period). Here, the contrast is the ratio of the luminance value of the specific area 212 of the second image 210 to the luminance value of the specific area 202 of the first image 200 (Loff _i / Lon with reference to FIG. 4). Therefore, changing the contrast of the specific area 212 of the second image 210 corresponds to changing the luminance value Loff _i of the specific area 212 of the second image 210 described above. Since Lon is constant, changing the contrast is equivalent to changing the luminance difference. That is, increasing the luminance difference linearly is equivalent to decreasing the contrast linearly, and decreasing the luminance difference linearly is equivalent to increasing the contrast linearly. Since the brightness value of the specific area 202 of the first image 200 is a constant value, this contrast can be said to be a normalized contrast.

In each period, the ratio c _i (the contrast A _i (hereinafter also referred to as a start value) of the specific area of the first second image 210 is decreased with time and the contrast of the specific area of the second image 210 is changed. (Slope of the graph) is decreased with time. Specifically, the contrast A _{i + 1 at} which measurement is started in the i + 1 period is set by A _{i + 1} = R _i + Δc _i , Δc _i = TB × c _i . Here, R _i is the contrast of the specific area of the second image 210 when the subject designates the specific area in the i-th period (for example, when a predetermined key is pressed). TB is a fixed time for determining the start value of the next measurement. That is, the start value is always determined by returning only by time TB, and the measurement is performed using the contrast used in the previous measurement in an overlapping manner. The overlap time TB and the slope c _i are set in advance.

  In each period, the position of the specific area in the two displayed images is randomly determined as described above. Therefore, for example, an image is displayed as shown in FIG. The images shown in FIG. 6 are sequentially displayed from left to right as time passes in each period. The specific area is the right sector area in the first period, the specific area is the left sector area in the second period, and the specific area is the upper sector area in the i period. Two image data whose values change are used.

  The control structure of the program for realizing the flicker perception threshold measurement method will be described below. In the following, it is assumed that the luminance of a pixel is represented by a gradation. For example, when a pixel is represented by 256 gradations (8 bits), the maximum luminance is represented by a gradation value “255”, and the minimum luminance is represented by a gradation value “0”.

Referring to FIG. 7, in step 300, CPU 102 performs initial setting. Specifically, the CPU 102 stores the start value A ₁ in the first period, the overlap time TB, and the slopes c _i (i = 1) in the first to Nth periods stored in the ROM 104 or the recording unit 108. Read ~ N). Multiple c _i is managed as a vector. The CPU 102 reads information on the correspondence between the operation unit 118 and the image partition area (for example, information on four keys corresponding to the four sector areas) stored in the ROM 104 or the recording unit 108.

In step 302, the CPU 102 determines a blinking condition. That, CPU 102 may, as the slope of the i-th period, to set the read _{c i} in step 300, calculates the time T0 (see FIG. 4) for displaying an image with the same contrast with this value. If step 302 is first executed, _{C 1} is used. As described above, when a digital image is used, the same image may be repeatedly displayed due to the relationship between the inclination and the number of gradations. The slope c _i is the contrast that is changed per unit time. The contrast “1” corresponds to the maximum gradation value Gmax, and the contrast “0” corresponds to the minimum value Gmin = 0. Therefore, the number of gradations that change per second is c _i × (Gmax−Gmin) = c _i × Gmax, and the time T0 for displaying an image changed by one gradation is T0 = 1 / (c _i × Gmax).

  In step 304, the CPU 102 generates a random number, determines the position of the specific area where the contrast is changed, and stores this position information in the RAM 106. For example, in the case of the images shown in FIGS. 3 and 6, one specific area is determined from four fan-shaped areas. Any known technique (such as a method for generating pseudo-random numbers using software, a method using thermal noise, etc.) may be used as a method for generating random numbers. In addition, a method of associating random numbers with the four sector regions is arbitrary. For example, an integer random number may be generated, and the four remainders (0, 1, 2, 3) may be associated with four sector regions.

In step 306, the CPU 102 generates two pieces of image data that are initially blinked in the i-th period using the conditions determined in steps 302 and 304, the start value A _i , and the overlap time TB. Further, the CPU 102 acquires the current time from the timer 110 and stores it in the RAM 106. In one image (corresponding to the first image 200 in FIG. 3), the brightness of the specific area is the maximum brightness Lon = Gmax, and in the other image (corresponding to the second image 210 in FIG. 3), the brightness of the specific area is , Lon × A _i . The luminance values of the other three fan-shaped regions are average values thereof, that is, Lon × (1 + A _i ) / 2.

  In step 308, the CPU 102 transmits the two image data generated in step 306 to the display unit 116 via the IF unit 112. Specifically, an image having a high luminance value in the specific area is transmitted, and image data having a low luminance in the specific area is transmitted after ΔT / 2, and then this is repeated. ΔT / 2 is ½ of the blinking period, and is a time equal to or longer than the refresh period of the display unit 116 (the reciprocal of the fixed refresh rate).

  In step 310, the CPU 102 determines whether or not the operation unit 118 has been operated. If it is determined that the operation has been performed, the received operation information is stored in the RAM 106, and the process proceeds to step 316. If it is determined that it has not been operated, the process proceeds to step 312.

  In step 312, the CPU 102 acquires the current time from the timer 110 and determines whether or not a predetermined time T 0 has elapsed from the time stored in the RAM 106 in step 306. When it is determined that the predetermined time has elapsed, the process proceeds to step 314. If it is determined that the predetermined time has not elapsed, the process returns to step 310. Thus, two images having the same contrast difference are alternately displayed during the time T0, and the operation unit 118 is waited to be operated.

  If the operation unit 118 is not operated, it is determined in step 314 whether or not a new image should be generated. As described above, if the subject does not operate, the contrast of the specific area of the second image 210 is reduced. If the value becomes 0 without being operated by the subject, the contrast cannot be further reduced, so steps 308 to 312 are repeated again under the same conditions.

In step 316, the CPU 102 generates the next image pair. Specifically, the brightness of a specific area of the second image 210 to be generated next is determined. In the i period, the initial value of the contrast of the specific area of the second image 210 is the start value A _i and decreases linearly with the slope c _i. Therefore, the contrast after t seconds from the start of each measurement period is A _i −c _i × t. Step 316 is executed every time T0. The luminance of the specific area of the second image 210 is Lon × (A _i −c _i × t). Using this value, first image data and second image data are generated in the same manner as in step 306. In the first image 200, the brightness of the specific area is not changed by Lon, but the brightness (intermediate value) of the other fan-shaped areas is changed to Lon × (1 + A _i −c _i × t) / 2. In the second image 210, the luminance of the specific region is changed to Lon × (A _i −c _i × t), and the luminance of the other fan-shaped regions is Lon × (1 + A _i −c _i × t) / Is changed to 2. Thereafter, the process returns to step 308, and the CPU 102 alternately transmits the two newly generated image data to the display unit 116, and the processes of steps 310 to 314 are repeated.

  In step 318, the CPU 102 determines whether or not the flickering area to which the subject has answered is correct, that is, whether or not the area designated by operating the operation unit 118 by the subject is the specific area. Specifically, it is determined whether or not the position information stored in the RAM 106 in Step 304 matches the operation information stored in the RAM 106 in Step 310. If it is correct (if it matches), the process proceeds to step 320. If it is not correct (if they do not match), the process returns to step 308, the CPU 102 transmits the same two image data to the display unit 116 again, and the processes of steps 310 to 314 are repeated.

  In step 320, the CPU 102 stores the contrast of the specific area of the second image 210 last transmitted to the display unit 116 in the RAM 106, and converges with the contrast stored in the RAM 106 by executing step 320 so far. Determine whether or not. The determination of convergence may be performed by an arbitrary method. For example, the CPU 102 can determine that the contrast has converged when the difference in contrast stored a plurality of times (for example, twice) is equal to or less than a predetermined value. If it is determined that the image has converged, the contrast stored last in the RAM 106 is stored in the recording unit 108 as a flicker perception threshold, and the process is terminated. If it is determined that it has not converged, the process proceeds to step 322.

In step 322, the CPU 102 changes the blinking condition. Specifically, when the measurement period to be executed next is the (i + 1) -th period, the start value A _{i + 1} is calculated by A _{i + 1} = R _i + Δc _i . Here, R _i is the contrast (contrast of a specific region of the second image 210) stored in the RAM 106 in step 320 in the immediately preceding measurement period (i period). Δc _i is calculated by Δc _i = TB × c _i using the overlap time TB and the slope ci when the contrast is linearly changed in the immediately preceding i-th period.

Thereafter, the processing returns to step 304, and the processing of steps 302 to 320 is executed using the condition (start value A _{i + 1} ) set in step 322.

  As described above, it is possible to adaptively set the measurement conditions (the position of the specific region, the start value, and the slope of the frequency or contrast change) and perform repeated measurement. As a result, the subject's flicker perception threshold (contrast of the specific region 212 of the second image 210 that was displayed when flicker began to be perceived) is measured from the same contrast in each measurement period, and the contrast is measured with the same inclination. It can be measured in a shorter time than when changing. Further, by determining whether the test subject's answer is correct or not, the test subject's arbitraryness can be eliminated, and an objective and accurate flicker perception threshold can be measured.

  Therefore, in the state where the subject is not fatigued, the flicker perceptual threshold value is measured and recorded as described above, and then the flicker perceptual threshold value obtained by measuring the same subject in the same manner is fatigued. It can be determined whether or not the subject is mentally fatigued by comparing with the flicker perceived value in the absence state.

The initial start value A ₁ of all measurements, the overlap time TB, and the slope c _i in each period can be set as appropriate in consideration of the refresh rate of the display unit 116 and the like. Preferably, the first starting value _{A 1} is 1, overlap time TB is 5～8S (s). Also preferably, the slope c _i is 0.004 to 0.02 s ⁻¹ . The start value A ₁ may be a value smaller than 1.

  These values may be set according to the subject. For example, the same subject can be determined using the previous measurement result.

Although the case where the contrast is linearly decreased in each measurement period has been described above, the contrast may be increased linearly. In that case, the start value A _i in each measurement period may be calculated using the above equation with the slope c _i set to a negative value. In the first image to be displayed, the luminance of all the divided areas is set to the maximum luminance. In the second image, the brightness of the area other than the specific area is set to the minimum brightness (minimum contrast), and the brightness (contrast) of the specific area is linearly increased from the minimum brightness (minimum contrast). If it does in this way, it will be in the state which a test subject perceives the flicker in all the areas | regions first, and if the brightness | luminance of the specific area of a 2nd image increases, a test subject will be in the state which cannot perceive the flicker of a specific area. At this time, the subject perceives flicker in a region other than the specific region. Therefore, if the specific region is randomly changed, the flicker perception threshold can be accurately measured in a short time without the subject's arbitraryness, as described above.

  Further, the image displayed for determining correctness is not limited to the image partitioned into the four areas shown in FIG. 3, and may be an image partitioned into at least two or more areas. For example, it may be an image of a seven segment partitioned into seven regions (numbers 0 to 9 are displayed by turning on / off seven minute regions).

  In addition, an image displayed for determining correctness may not be an image divided into a plurality of areas. For example, it is possible to use two images in which any one character of a single-digit number (0 to 9) or alphabet (A to Z) is displayed on a uniform background. In this case, the luminance is changed with the character area in the second image as the specific area. If the brightness difference is small, the subject cannot recognize the characters. When the brightness difference in the character area decreases, the subject can perceive flicker and can recognize the character. The subject's flicker perception threshold can be similarly measured by determining whether or not the subject has recognized the character and correctly pressed the corresponding numeric key or alphabet key.

Moreover, although the case where the CPU 102 generates image data in real time has been described above, the present invention is not limited to this. Image data of a possible pattern is generated according to a combination of conditions (number of gradations, start value A ₁ , overlap time TB, slope c _i, etc.), and each or all of the image data is specified. The image data may be stored in the recording unit 108 in association with the information, and the corresponding image data may be read with reference to information for specifying the image as appropriate.

  Moreover, although the case where the brightness | luminance of area | regions other than two specific areas was the average value of two specific areas in two images was demonstrated, it is not limited to this. The brightness of the area other than the specific area may be a constant value between the brightness value of the specific area of the first image and the brightness value of the specific area of the second image.

In the above description, the adaptive method capable of shortening the measurement time when measuring the flicker perception threshold using a display device with a fixed refresh rate has been described. However, the adaptive method is a conventional flicker test. Similarly to the above, it can be applied to a method of measuring CFF by changing the blinking frequency. In the conventional flicker test, as shown in FIG. 1, the frequency is decreased with the passage of time from the start point (start frequency fs), and the frequency when the subject can perceive blinking is determined as a threshold value. Usually, the measurement start frequency fs is set to a sufficiently high value with a margin so that any subject can be accommodated. Therefore, when measuring several times (for example, 5 times), it took a long time. On the other hand, when the stimulus is presented by changing the blinking frequency in order to shorten the measurement time, for example, the vertical axis in FIG. That is, if the start value A _i in each measurement period is the measurement start frequency, the slope c _i is the frequency change amount per unit time, and the appropriately set overlap time TB is used, the arbitraryness of the subject cannot be excluded. However, it is possible to measure CFF in a shorter time than when measuring with the same start frequency and the same slope.

In the above, the case where the measurement start value and the slope in each measurement period are determined adaptively in order to shorten the measurement time has been described. However, the measurement time can be shortened only by appropriately setting the measurement start value. . As described above, in the conventional flicker test, the measurement start frequency is set to a sufficiently high value with a margin so that any subject can be accommodated. On the other hand, when measuring with respect to a specific individual, it is not necessary to start measurement from a frequency higher than necessary, and the range that can cover the fluctuation range in which the threshold varies depending on the individual condition and the fluctuation range of the threshold in the measurement itself. If it can measure by. As an example, when a previous measurement value of a subject is f _j , it rarely fluctuates 10% or more from that value. Therefore, the past measurement value result is recorded, and the start measurement frequency f _{j + 1} is set as f _{j + 1} = f _j + 0.1 × f _j using the previous measurement value f _j . The coefficient 0.1 can be reduced as long as the measurement accuracy is maintained. Thereby, the measurement time can be shortened.

Similarly, when measuring by changing the contrast with respect to a particular subject, a start value A ₁ in the first measurement period, the previous measurement result using the (flicker perception _{threshold) R, A 1 = R +} 0.1 × R If it is set, the measurement time can be further shortened.

  The present invention has been described above by describing the embodiment. However, the above-described embodiment is an exemplification, and the present invention is not limited to the above-described embodiment, and is implemented with various modifications. be able to.

  The experimental results are shown below to show the effectiveness of the present invention.

  A method of measuring a flicker perception threshold of the present invention (hereinafter also referred to as a high-speed flicker perception threshold inspection method), that is, a method of measuring by setting adaptively measurement conditions (starting point and slope of frequency or contrast change); The flicker perception threshold was measured for the same subject using the measurement method without changing the measurement conditions. In either method, the subject is presented with a figure divided into four areas as shown in FIG. 3 while changing the contrast, and one blinking area is selected from the four areas (the position of the blinking area is repeated). A four-choice flicker test was performed to select (change randomly at each measurement). Each method was examined 10 times. FIG. 8 shows an average value of the time required for the inspection in each method (the time from the start until the measurement value converges). The left bar graph is the result when measurement is performed without changing the measurement condition, and the right bar graph is the result when measurement is performed while adaptively changing the measurement condition. In each case, the variation from the average value is indicated by an error bar. Since the p-value of the test is as very small as 0.00016, the measurement result is significant.

  The specific average value was 66.5 ± 16.2 seconds when the measurement conditions were not changed, and 38.4 ± 5.9 seconds when the measurement conditions were adaptively changed. Thus, according to the high-speed flicker perception threshold inspection method of the present invention, the flicker perception threshold can be measured in a short time of about 40 seconds.

  The conventional flicker inspection with changing frequency takes 3 to 4 minutes to measure. Even when the measurement conditions are not changed, the measurement time can be shortened to about 1 minute by the four-choice flicker inspection that changes the contrast. In order to put it into practical use as a daily simple fatigue measurement method, it is desirable to be able to measure in a shorter time. In this regard, the measurement method of the present invention that can measure in a shorter time is effective.

  Further, it will be shown below that the flicker perception threshold measured by the high-speed flicker perception threshold inspection method of the present invention has a high correlation with the conventional flicker inspection value.

  The subjects were asked to perform office work all night from 4:00 pm (16:00) on the first day to 7:00 am (7:00) on the second day. Measurements were made at regular intervals using the conventional flicker inspection method and the high-speed flicker perception threshold inspection method of the present invention. In order to evaluate the recovery state of the subject's fatigue after the subject sleeps for 4 hours after the end of office work all night, measurement is performed by both inspection methods at 2 pm (14:00) on the second day. did. The upper graph in FIG. 9 shows the time transition of the fatigue measurement values measured by both inspection methods, and the lower graph in FIG. 9 shows the correlation analysis result between the fatigue measurement values measured by both measurement methods. ing.

  In FIG. 9, “Original Flicker” represents a measurement value obtained by the conventional flicker inspection method, and “Fast Flicker” represents a measurement value obtained by the high-speed flicker perception threshold inspection method of the present invention. The vertical axis is the flicker perception threshold normalized by the measurement at the start of the experiment (the value obtained by dividing the measured value at each time by the measured value at the start of the experiment).

  From the graph in the upper part of FIG. 9, it can be seen that in any method, mental fatigue due to working all night is accumulated over time from early morning to morning, and the state of recovery by sleep can be measured. Further, from the lower graph (scatter diagram), the correlation coefficient R is 0.956 and a value close to 1, and the flicker test value that has been widely used in the past is the measurement value obtained by the high-speed flicker perception threshold test method of the present invention. It can be seen that there is a high positive correlation. The straight line in the lower graph of FIG. 9 is a straight line of y = 1.588x−0.589 where y is a measured value by the high-speed flicker perception threshold test method of the present invention and x is a measured value by the conventional flicker test method. It is. Since p = 0.00075 is small, the measurement result is significant.

100 Flicker Perception Threshold Measurement Device 102 Arithmetic Processing Unit (CPU)
104 Read-only memory (ROM)
106 Rewritable memory (RAM)
108 Recording unit 110 Timer 112 Interface unit (IF unit)
114 Bus 116 Display 118 Operation Unit 200 First Image 210 Second Image 202, 212 Specific Area

Claims (7)

A method of measuring a flicker perception threshold of a subject by presenting a blinking stimulus to the subject,
The blinking stimulus is a stimulus in which one of the luminance difference and the frequency is a constant value and the other is changed,
Presenting the flashing stimulus by changing the other from the start value, changing the slope of the other change amount per unit time to be constant with the passage of time;
In the state where the flashing stimulus is presented, the process of determining the other value as a temporary threshold when the subject perceives flickering due to the flashing stimulus and operates the operation unit is performed as one measurement, and the measurement is performed. A step repeated several times;
The value obtained by adding the provisional threshold determined in the measurement to the value obtained by multiplying the slope used in one measurement by a predetermined time is used as the next measurement after the measurement. A starting value determining step for determining as a starting value in
Determining a flicker perception threshold for the subject using a plurality of the temporary thresholds obtained by a plurality of the measurements,
A method for measuring a flicker perception threshold, wherein a new slope having an absolute value smaller than an absolute value of the slope used in one measurement is used in a subsequent measurement.   When measuring the flicker perception threshold of a subject, the flicker perception threshold obtained by the previous measurement for the subject is used as the other start value in the first measurement period. The flicker perception threshold according to claim 1, wherein a value obtained by decreasing at a ratio is used, and if the other change is a decrease, a value obtained by increasing at a predetermined ratio is used. Measuring method. Said one is a frequency,
The other is a luminance difference,
The blinking stimulus is a stimulus generated by alternately presenting regions having two different luminances at the same position at a constant frequency,
The method of measuring a flicker perception threshold according to claim 1 or 2, wherein the luminance difference is changed by changing a lower luminance while maintaining a higher luminance of the two luminances. The areas having two different luminances are specific areas on two images, respectively.
The two images are partitioned into a plurality of regions with the same pattern,
The specific region is one of a plurality of the regions randomly determined for each measurement,
The operation of the operation unit by the subject is an operation of selecting one of the plurality of regions as the specific region,
If the selection by the subject in a single measurement is correct, the start value determination step is performed and a new slope having an absolute value smaller than the absolute value of the slope used in the measurement is measured. Used in the next measurement of
If the selection by the subject in one measurement is incorrect, do not perform the start value determining step and use the start value and slope used in the measurement in the next measurement The method of assuming a flicker perception threshold according to claim 3. A method of measuring a flicker perception threshold of a subject by presenting a blinking stimulus to the subject,
The blinking stimulus is a stimulus in which one of the luminance difference and the frequency is a constant value and the other is changed,
Presenting the flashing stimulus by changing the other from the start value, changing the slope of the other change amount per unit time to be constant with the passage of time;
In the state where the flashing stimulus is presented, the process of determining the other value as a temporary threshold when the subject perceives flickering due to the flashing stimulus and operates the operation unit is performed as one measurement, and the measurement is performed. Including a step of repeating a plurality of times,
The starting value is obtained by reducing the flicker perception threshold obtained by measurements performed on the subject prior to the plurality of measurements, by decreasing a predetermined ratio when the other change is an increase. A method for measuring a flicker perception threshold, characterized in that when the other change is a decrease, the flicker perception threshold is a value obtained by increasing at a predetermined ratio. A device for measuring a perceptual threshold comprising a display unit and an operation unit for displaying a blinking stimulus to a subject,
The blinking stimulus is a stimulus in which one of the luminance difference and the frequency is a constant value and the other is changed,
In the state in which the other is changed from the start value and the slope, which is the other change amount per unit time, is made constant and the blinking stimulus is displayed while the blinking stimulus is displayed, the subject performs the blinking stimulus. The process of determining the other value as a temporary threshold when the operation unit is operated while perceiving flickering, as a single measurement, repeating the measurement a plurality of times,
Use a new slope having an absolute value smaller than the absolute value of the slope used in one of the measurements in the next measurement of the measurement;
The value obtained by adding the provisional threshold determined in the measurement to the value obtained by multiplying the slope used in one measurement by a predetermined time is used as the next measurement after the measurement. The starting value at
An apparatus for measuring a flicker perception threshold, wherein the flicker perception threshold of the subject is determined using a plurality of the provisional thresholds obtained by a plurality of the measurements. To a computer or portable terminal device having an operation unit and a display unit
One of the luminance difference and the frequency is set to a constant value, and the other is changed from the start value to the slope, which is the other change amount per unit time, with the passage of time. The ability to display flashing stimuli;
In a state where the blinking stimulus is displayed, a process of determining the other value as a temporary threshold when the subject perceives flickering due to the blinking stimulus and operates the operation unit, as one measurement, the measurement A function that repeats multiple times,
The value obtained by adding the provisional threshold determined in the measurement to the value obtained by multiplying the slope used in one measurement by a predetermined time is used as the next measurement after the measurement. A function to determine the starting value at
Using a plurality of the temporary thresholds obtained by a plurality of the measurements, realizing a function of determining the flicker perception threshold of the subject,
A flicker perception threshold measurement program characterized in that a new gradient having an absolute value smaller than the absolute value of the gradient used in one measurement is used in the next measurement of the measurement.

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