A measurement system for spatial contrast sensitivity curve

Abstract

The present invention discloses a measurement system for spatial contrast sensitivity curves, which includes a parameter acquisition module, a visual stimulus generation module, a human-computer interaction module, a process control module, and a data recording and analysis module. The parameter acquisition module acquires the measurement type and measurement parameters; the visual stimulus generation module generates non-color visual stimuli or color visual stimuli for measurement; the human-computer interaction module displays the visual stimuli to the individual to be measured and acquires the identification situation of the individual to be measured with respect to the visual stimuli; the process control module adjusts the contrast of the visual stimuli and controls the measurement process; the data recording and analysis module records the measurement information and analyzes and determines the spatial contrast sensitivity curve. The measurement system for spatial contrast sensitivity curves provided by the present invention can not only measure the luminance spatial contrast sensitivity, but also measure the color spatial contrast sensitivity. At the same time, the measurement accuracy is high, and it is applicable to the evaluation of the functions of infants, young children or animals, and has a broader application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of spatial contrast sensitivity detection, and particularly relates to a measurement system for a spatial contrast sensitivity curve. Background Art

[0002] The Spatial Contrast Sensitivity Function (SCSF) is often simply referred to as the contrast sensitivity curve, which is a curve describing the ability of the visual system of humans or animals to perceive information at different spatial frequencies, and can intuitively and comprehensively reflect the basic functional status of the visual system.

[0003] Currently, the existing devices or systems for measuring the spatial contrast sensitivity curve have many deficiencies. For example, the spatial frequency to be measured is fixed and cannot be effectively adjusted according to the situation of the individual being measured; when measuring, preset contrast levels are mostly used, and the intervals between the levels are not standardized, resulting in uneven differences between the levels and affecting the measurement accuracy.

[0004] More importantly, the established process control and data analysis methods in the existing measurement devices or systems have certain defects in theory and cannot take into account both measurement accuracy and accuracy. The measurement theory of the existing system believes that the measurement results should correspond to the data points that the user can correctly identify 100%. However, psychophysical research has shown that when the stimulus intensity (such as contrast) gradually increases, the visual system will experience a process from "invisible" to "visible", but this is not an abrupt change but a gradual change. In psychophysics, the psychophysical measurement curve is often used to describe the relationship between the stimulus intensity and the perception result of the individual being measured, as shown in Figure 1 As shown. The psychophysical measurement curve is in an "S" shape. In psychophysics, generally, the stimulus intensity corresponding to a certain specific correct perception probability on the relatively steep middle section of the S-shaped measurement curve is used as the perception "threshold" of the individual being measured to represent the functional level of the individual being measured. On this basis, the thresholds corresponding to the same correct perception probability can be compared among different individuals to distinguish the high and low levels of individual functional levels. Therefore, the threshold point should be set on the relatively steep middle section of the S-shaped measurement curve, and its theoretical position should be ensured through appropriate process control and data analysis methods (for example, the ordinate corresponds to 75%), so as to effectively take into account both measurement accuracy and accuracy.

[0005] In addition, most of the existing measurement devices or systems use sine gratings as visual stimuli. However, for infants and young children with poor comprehension and difficulty in concentrating their attention for a long time, or animals that cannot communicate effectively, simple graphic stimuli are more likely to arouse interest and are more convenient to identify than grating stimuli. The children's visual acuity chart using simple graphics is a typical example.

[0006] Finally, existing measurement devices or systems can only use non-color (black, white, and gray) stimuli to evaluate the luminance spatial contrast sensitivity curve of humans or animals, and cannot evaluate the color spatial contrast sensitivity based on color stimuli. Summary of the Invention

[0007] The object of the present invention is to provide a technical solution for a measurement system of spatial contrast sensitivity curve in view of the deficiencies of the existing technology. Aiming at the defects in the existing technology, it can not only complete the measurement of luminance spatial contrast sensitivity, but also measure the color spatial contrast sensitivity. Moreover, it overcomes the shortcomings of traditional measurement systems. It can adjust the measurement range and measurement accuracy according to the actual application needs, has strong universality, and can take into account measurement accuracy and accuracy through the design of measurement and analysis processes. It can also reduce the use difficulty through the application of graphic stimuli, is suitable for the evaluation of infant or animal functions, and has a broader application prospect.

[0008] To solve the above technical problems, the present invention adopts the following technical solutions:

[0009] A measurement system of spatial contrast sensitivity curve, comprising:

[0010] A parameter acquisition module, which acquires the measurement type and measurement parameters. The measurement type includes luminance spatial contrast sensitivity and color spatial contrast sensitivity. The common measurement parameters include multiple spatial frequencies to be measured, the maximum test amount at a single spatial frequency to be measured, and the minimum change unit of the contrast corresponding to the spatial frequency to be measured. If the measurement type is color spatial contrast sensitivity, two colors need to be selected from the three colors of red, green, and blue, where the first color is the color used as the background, and the first color and the second color are the colors used as stimuli;

[0011] A visual stimulus generation module, which generates visual stimuli for measurement based on the parameters acquired by the parameter acquisition module and the built-in parameters of the system. The visual stimuli include non-color visual stimuli or color visual stimuli;

[0012] A human-computer interaction module, which presents the generated visual stimuli to the individual to be measured and acquires the correct / incorrect identification situation of the individual to be measured for the visual stimuli;

[0013] A process control module, which continuously adjusts the contrast of the visual stimuli presented to the individual to be measured based on the response of the individual to be measured to the visual stimuli. The contrast of the visual stimuli includes the luminance contrast of non-color visual stimuli or the color contrast of color visual stimuli, until the identification situation of the individual to be measured for the visual stimuli reaches the specified requirements;

[0014] The data recording and analysis module records all visual stimulus contrasts during the measurement process, as well as the response data of the individual being measured, analyzes and determines the sensitivity of the individual being measured at multiple spatial frequencies to be measured, and based on this, plots a spatial contrast sensitivity curve, which includes a luminance spatial contrast sensitivity curve or a color spatial contrast sensitivity curve.

[0015] Furthermore, the minimum change unit of the contrast corresponding to the spatial frequency to be measured ranges from 0.5 to 6.0 dB, and different initial values are selected at different spatial frequencies to be measured, and then gradually decrease as the measurement progresses.

[0016] Furthermore, for spatial frequencies greater than 4 cycles / degree, the initial value of the minimum change unit of the contrast is 3.0 dB. After completing the initial 6 trial measurements, it is adjusted to 1 / 3 of the initial value, that is, 1.0 dB;

[0017] For spatial frequencies less than or equal to 4 cycles / degree, the initial value of the minimum change unit of the contrast is 4.5 dB. After completing the initial 6 trial measurements, it is adjusted to 1 / 3 of the initial value, that is, 1.5 dB.

[0018] Furthermore, the parameter acquisition module also needs to acquire parameters related to the visual stimulus attributes, including the size, presentation time of the visual stimulus, and auxiliary features related to the visual stimulus identification. And there are two or more visual stimulus attribute options in the test for the individual being measured to identify, and the two visual stimulus attribute options differ in azimuth by π / 2 radians, such as π / 4 and 3π / 4.

[0019] Furthermore, the size of the visual stimulus is marked by the diameter, and the diameter size ranges from 2.5 to 6.0 degrees of visual angle. The presentation time of the visual stimulus ranges from 50 to 250 milliseconds, and the presentation time of the visual stimulus is preferably 150 milliseconds.

[0020] Furthermore, the auxiliary features related to the visual stimulus identification are shape, orientation or azimuth, and the auxiliary feature is preferably the azimuth feature.

[0021] Furthermore, the achromatic visual stimulus includes an achromatic graphic stimulus and an achromatic grating stimulus. The achromatic visual stimulus is presented on a uniform gray background, and part or all of the achromatic visual stimulus has a different luminance from the background. The difficulty of identifying the achromatic visual stimulus is indicated by the luminance contrast C l of the achromatic visual stimulus.

[0022] Furthermore, the achromatic graphic stimulus is a stimulus image drawn with non - colored lines of uniform thickness. The line thickness should meet the following requirements:

[0023] ;

[0024] Among them, f is the spatial frequency to be measured, with the unit of cycle / degree; DPD is the visual angle occupied by each point in the stimulus image, with the unit of degree / point;

[0025] The luminance contrast C of the achromatic graphic stimulus l is defined as:

[0026] ;

[0027] Among them, l pattern represents the luminance of the achromatic graphic stimulus, L mean is the average background luminance, and abs(·) is the absolute value function;

[0028] The achromatic grating stimulus is constructed according to the following function:

[0029] ;

[0030] Among them, l(x, y) represents the luminance of the point with coordinates (x, y) on the stimulus image, L mean is the average background luminance, C l is the luminance contrast of the achromatic grating stimulus; f is the spatial frequency to be measured; DPD is the visual angle occupied by each point in the stimulus image, with the unit of degree / point; θ is the grating orientation (for auxiliary features related to stimulus identification), and φ is the grating phase. Preferably, L mean takes 0.5, and θ takes π / 4 or 3π / 4.

[0031] Furthermore, the color visual stimulus includes a color graphic stimulus and a color grating stimulus. The color visual stimulus is presented on a unified background. The color visual stimulus and the background have exactly the same luminance but present different colors. The background only contains the first color, and the color of the color visual stimulus is a mixture of the first color and the second color. The difficulty of identifying the color visual stimulus is indicated by the color contrast C C of the stimulus, and preferably, the first color is red and the second color is green.

[0032] Furthermore, the color graphic stimulus is a stimulus image drawn with lines of uniform thickness, and the following requirements should be met during drawing:

[0033] ;

[0034] ;

[0035] ;

[0036] Among them, f is the spatial frequency to be measured, with the unit of cycle / degree; DPD is the visual angle occupied by each point in the stimulus image, with the unit of degree / point; C CColor contrast for color graphic stimuli: L mean，color1 Represents the background luminance, l pattern，color1 Represents the luminance corresponding to the first color in the color graphic stimulus, l pattern，color2 Represents the luminance corresponding to the second color in the color graphic stimulus;

[0037] The color raster stimulus is generated according to the following formula:

[0038] ;

[0039] ;

[0040] ;

[0041] where l(x, y) represents the luminance of the point with coordinates (x, y) on the stimulus image; l(x, y) colorl represents the luminance corresponding to the first color in the luminance of this point; l(x, y) color2 represents the luminance corresponding to the second color in the luminance of this point, L mean , color1 represents the background luminance with the first color; C C is the color contrast of the color raster stimulus; f is the spatial frequency to be measured, DPD is the visual angle occupied by each point in the stimulus image, in degrees / point; θ is the grating orientation, φ is the grating phase, preferably, L mean takes 0.5, and θ takes π / 4 or 3π / 4.

[0042] Furthermore, the human-computer interaction module includes a luminance evaluation and conversion unit. The luminance evaluation and conversion unit regularly evaluates the luminance distribution of the display device at different hardware luminance levels and converts the theoretical luminance value of the visual stimulus to be presented into a hardware luminance level value that meets the requirements;

[0043] The specific working steps of the luminance evaluation and conversion unit are as follows:

[0044] S1-1. With the hardware settings of the display device fixed, evaluate and record the actual screen luminance at each hardware luminance level one by one according to the hardware luminance level prompted by the display device bit depth;

[0045] S1-2. Use the following formula to perform data fitting on the evaluation data:

[0046] ;

[0047] where l is the actual screen luminance; x is the hardware luminance level; a1, a2, b1, b2, BP are all fitting parameters; min(·) is the minimum value function;

[0048] S1-3. When presenting a visual stimulus, convert the theoretical brightness value required for each pixel of the visual stimulus transmitted by the visual stimulus generation module into the hardware brightness level value that should be used for each pixel during actual presentation according to the formula in S1-2.

[0049] Furthermore, the human-computer interaction module also includes a jaw support and distance evaluation unit. The specific work of the jaw support and distance evaluation unit is as follows: The jaw support is used to fix the lower jaw of the individual being measured during the measurement process. During the measurement process, the distance between the screen presenting the visual stimulus and the jaw support is evaluated in real time through a distance sensor. When the relative difference between the evaluated distance and the specified measurement distance exceeds 5% of the specified measurement distance, a voice prompt of "correct the distance" is given.

[0050] Furthermore, in the process control module, based on the reaction of the individual being measured to the visual stimulus, the specific steps for continuously adjusting the contrast of the visual stimulus presented to the individual being measured are as follows:

[0051] S2-1. If the current trial is the first trial at the to-be-tested spatial frequency, the visual stimulus contrast uses the default value;

[0052] S2-2. If in the previous trial, the result of the individual being measured identifying the visual stimulus is correct, then in the next trial presenting the visual stimulus at the same to-be-tested spatial frequency, the visual stimulus contrast is reduced by 1 minimum change unit; if the identification result in the previous trial is incorrect, then in the next trial presenting the visual stimulus at the same to-be-tested spatial frequency, the visual stimulus contrast is increased by the first specified number of minimum change units; where the first specified number is a positive integer greater than 1; preferably, the first specified number is 3;

[0053] S2-3. At the current to-be-tested spatial frequency, if the number of trials presented to the individual being measured has reached the set maximum test quantity, or the visual stimulus contrast presented to the individual being measured fluctuates repeatedly within the first specified range, or the visual stimulus contrast has reached the upper and lower limits of the measured range of the visual stimulus contrast continuously 3 times or cumulatively 5 times, then terminate the test at this spatial frequency and no longer adjust the contrast of the visual stimulus at this spatial frequency. Preferably, the first specified range is 5 minimum change units of contrast.

[0054] Furthermore, in the data recording and analysis module, the specific steps for analyzing and determining the sensitivity of the individual being measured at multiple to-be-tested spatial frequencies and plotting the spatial contrast sensitivity curve include:

[0055] S3-1. Based on the recorded data, select a to-be-tested spatial frequency, list the visual stimulus contrast used in each trial and the correct / incorrect situation of the individual being measured's identification of the visual stimulus in the order of trials that occurred during actual measurement at this spatial frequency;

[0056] S3-2. Based on the list compiled in S3-1, select the visual stimulus contrast at which the trend of the visual stimulus contrast changes during the measurement process, and record it as C cri ;

[0057] S3-3, if the spatial frequency C cri If the number is less than the second specified number, the analysis is terminated and a prompt "the threshold cannot be determined and re-measurement should be performed" is displayed; otherwise, the process proceeds to step S3-4; preferably, the second specified number is 10;

[0058] S3-4, if all C cri If the difference between the maximum and minimum values does not exceed the third specified number of contrast minimum change units, then all C cri The reciprocal of the arithmetic mean of is the contrast sensitivity of the measured individual at the spatial frequency; otherwise, proceed to step S3-5; preferably, the third specified number is 5;

[0059] S3-5, in all C cri In the order of appearance, remove the first 3 or 4 C cri , so that the remaining C cri The number of is even, then take all the remaining C cri The reciprocal of the arithmetic mean of the measured individual at this spatial frequency is the result;

[0060] S3-6, executing steps S3-1 to S3-5 in sequence at all the spatial frequencies to be measured, to obtain the contrast sensitivity of the measured individual at all the spatial frequencies to be measured;

[0061] S3-7. Based on the contrast sensitivity of the measured individual at all measured spatial frequencies obtained in S3-6, a spatial contrast sensitivity curve is plotted on a double logarithmic coordinate axis with the measured spatial frequency as the horizontal axis and the contrast sensitivity as the vertical axis.

[0062] Furthermore, in step S2-3, the stimulus contrast presented to the measured individual repeatedly fluctuates within the first specified range, specifically: the contrast of the stimulus ... cri Based on the first specified range, the fourth specified number of C cri The value range of the fourth specified number is 6 to 20, and preferably, the fourth specified number is 8.

[0063] The present invention has the following beneficial effects due to the adoption of the above technical solution:

[0064] The present invention can not only complete the measurement of luminance spatial contrast sensitivity, but also measure color spatial contrast sensitivity. Moreover, it overcomes the disadvantages of traditional measurement systems, can adjust the measurement range and measurement accuracy according to the needs of actual applications, has strong universality, can balance measurement accuracy and accuracy through the design of measurement and analysis processes, and can also reduce the difficulty of use through the application of graphical stimuli. It is applicable to the evaluation of infant or animal functions and has a broader application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] The present invention will be further described below with reference to the accompanying drawings:

[0066] Figure 1 is the psychophysical measurement curve of the present invention;

[0067] Figure 2 is an example diagram of a measurement system for a spatial contrast sensitivity curve of the present invention;

[0068] Figure 3 is the visual stimulus schematic diagram of the present invention;

[0069] Figure 4 is the schematic diagram of the test process at a certain spatial frequency in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0070] As Figure 2 shown, a measurement system for a spatial contrast sensitivity curve of the present invention includes:

[0071] (1) A parameter acquisition module that acquires the measurement type and measurement parameters. The measurement type includes luminance spatial contrast sensitivity and color spatial contrast sensitivity. The general measurement parameters include multiple spatial frequencies to be measured, the maximum test amount at a single spatial frequency to be measured, and the minimum change unit of the contrast corresponding to the spatial frequency to be measured; if the measurement type is color spatial contrast sensitivity, two colors need to be selected from the three colors of red, green, and blue, where the first color is the color used as the background, and the first color and the second color are the colors used as stimuli;

[0072] (2) A visual stimulus generation module that generates visual stimuli for measurement based on the parameters acquired by the parameter acquisition module and the built-in parameters of the system. The visual stimuli include achromatic visual stimuli or chromatic visual stimuli;

[0073] (3) A human-computer interaction module that presents the generated visual stimuli to the individual to be measured and acquires the correct / wrong situation of the individual to be measured's identification of the visual stimuli;

[0074] (4) A process control module that continuously adjusts the visual stimulus contrast presented to the individual being measured based on the response of the individual being measured to the visual stimulus. The visual stimulus contrast includes the luminance contrast of achromatic visual stimuli or the color contrast of chromatic visual stimuli, until the identification of the visual stimulus by the individual being measured meets the specified requirements.

[0075] (5) A data recording and analysis module that records all visual stimulus contrasts during the measurement process, as well as the response data of the individual being measured, analyzes and determines the sensitivity of the individual being measured at multiple spatial frequencies to be measured, and based on this, plots a spatial contrast sensitivity curve. The spatial contrast sensitivity curve includes a luminance spatial contrast sensitivity curve or a color spatial contrast sensitivity curve.

[0076] Among them, the spatial frequency to be measured obtained by the parameter acquisition module can be any value greater than 0. However, considering the limitations of measurement conditions and the actual situation of primates, the spatial frequency to be measured should not exceed 45.0 cycles / degree. In addition, limited by the size of the stimulus (generally not exceeding a 6-degree visual angle when only considering imaging in the macula of the retina), to ensure the integrity of the presented stimulus (for example, when presenting a grating stimulus, the number of cycles included in the stimulus should be greater than 1), the spatial frequency to be measured should not be lower than 0.2 cycles / degree. Generally, the value range of the spatial frequency to be measured is 0.5 - 36.0 cycles / degree. Of course, during actual measurement, the value range of the spatial frequency can also be limited to a smaller area, such as 2.0 - 8.0 cycles / degree, to specifically evaluate the functional level or functional defects of an individual (such as a specific patient population or animal). Compared with the situation of fixed test spatial frequencies in many existing spatial contrast sensitivity measurement systems, the above settings of this system solve the problem that the evaluation range needs to be frequently adjusted, which is commonly found in clinical and basic research, and effectively expand the application scenarios and application scope of spatial contrast sensitivity evaluation.

[0077] The maximum test quantity at a single spatial frequency to be measured obtained by the parameter acquisition module is related to the test completion time. If the maximum test quantity is large, the test completion time is relatively long. Generally, the maximum test quantity is 60 - 120 trials; preferably, the maximum test quantity can be set to 80 trials. Among them, one trial represents "presenting a stimulus once and receiving the identification situation of the individual being measured for the presented stimulus this time".

[0078] The minimum change unit of the contrast corresponding to the spatial frequency to be measured, obtained by the parameter acquisition module, is directly related to the measurement accuracy. The minimum change unit of the contrast is equivalent to the minimum scale of the measuring tool (such as a meter stick or a vernier caliper) in length measurement. Therefore, the smaller the minimum change unit, the higher the corresponding measurement accuracy. Of course, the minimum change unit is not as small as possible. According to the process control rules applied in this system (see details later), the smaller the minimum change unit, the longer the process of presenting stimuli during measurement from the initial level to the level corresponding to the true functional level of the individual being measured (see "Phase 1" in Figure 4 ). The more trials and time are consumed. When the test volume at a single spatial frequency to be measured is fixed, the more trials are consumed in Phase 1, the fewer trials there are in Phase 2, which has a decisive impact on the measurement result. The less data can be obtained in Phase 2, and the lower the accuracy of the measurement result (see details later for the data analysis method in Phase 2 and its relationship with the measurement result). Therefore, there is no need to overly pursue a small minimum change unit.

[0079] Generally, the minimum change unit should be determined before measurement and remain stable during the measurement process. A stable minimum change unit means that the gap between two adjacent difficulty levels defined by the minimum change unit is fixed. This helps to control the errors in the measurement process and ensure the accuracy of the measurement result. Currently, the visual acuity charts used for vision examination in China have gone through the development process from "unequidistant" to "equidistant". In the early visual acuity charts, the decimal method was used to measure visual acuity. Between the three levels of 0.6, 0.8, and 1.0, there were also two levels of 0.7 and 0.9. However, in the new and currently widely used international standard logarithmic visual acuity chart, these two levels of 0.7 and 0.9 have been deleted. This is because these two levels do not conform to the equidistant principle applied in the international standard logarithmic visual acuity chart. In the international standard logarithmic visual acuity chart, visual acuity is measured using the more scientific logarithmic 5-point method, and the gap between each adjacent visual acuity level is fixed at 0.1. When converting from the traditional decimal visual acuity level to the logarithmic 5-point visual acuity level, 0.6 corresponds to 4.8, 0.7 corresponds to 4.85, 0.8 corresponds to 4.9, 0.9 corresponds to 4.95, and 1.0 corresponds to 5.0. It can be seen that from the measurement standard of logarithmic 5-point visual acuity, the gap between the two visual acuity levels of 0.7 and 0.9 and the adjacent visual acuity levels is only 0.05, which does not meet the standard of "the gap between adjacent levels is fixed at 0.1", so they are finally deleted.

[0080] The above introduction about the distance of visual acuity levels actually brings up another key issue. That is, how should the minimum change unit, or the gap between adjacent difficulty levels, be measured? The traditional decimal visual acuity measurement method more or less reflects the idea of linear measurement. However, in fact, the "Weber-Fechner law" has revealed that the sensory quantity is logarithmically linearly related to the physical stimulus quantity, rather than linearly related to the physical stimulus quantity itself. Therefore, the minimum change unit of contrast should follow the logarithmic change principle, just like the logarithmic 5-point measurement method of the international standard visual acuity chart, rather than the linear change principle. That is, the relationship between three adjacent and equally spaced difficulty / contrast levels ( , and ) used in the measurement should be , or , rather than .

[0081] In addition, the signal energy carried by visual stimuli is related to the contrast of the stimuli, and the formula is:

[0082] ;

[0083] where is the contrast of the point with coordinates on the visual stimulus, that is:

[0084] ;

[0085] where is the brightness of the point with coordinates on the visual stimulus, is the background brightness of the visual stimulus.

[0086] Based on the above characteristics, the minimum change unit of contrast can be defined using the dB notation commonly used in engineering, specifically:

[0087] ;

[0088] Therefore, a difference of 1.0 dB is approximately a 1.122-fold difference in contrast. In actual use, it is generally selected as appropriate within the range of 0.5 - 6.0 dB.

[0089] In addition, the visual systems of humans and animals have a characteristic, that is, they have different sensitivities to different spatial frequencies. For example, the visual system of a normal person has a sensitivity exceeding 100 to medium spatial frequencies (for example, 2 cycles / degree), while the sensitivity to high spatial frequencies (for example, 24 cycles / degree) is less than 10. Therefore, different minimum change units of contrast can be set for different spatial frequencies. For example, for spatial frequencies greater than 4 cycles / degree, the minimum change unit of contrast can be set to 1.0 dB, while for spatial frequencies less than or equal to 4 cycles / degree, the minimum change unit of contrast can be set to 1.5 dB. In addition, to quickly pass through "Stage 1" during the test process, a larger minimum change unit of contrast can be selected in the first few trials of measurement. Preferably, for spatial frequencies greater than 4 cycles / degree, the initial value of the minimum change unit of contrast is 3.0 dB, and after completing the measurement of the first 6 trials, it is adjusted to 1.0 dB; for spatial frequencies less than or equal to 4 cycles / degree, the initial value of the minimum change unit of contrast is 4.5 dB, and after completing the measurement of the first 6 trials, it is adjusted to 1.5 dB.

[0090] In addition, if the measurement type is "luminance spatial contrast sensitivity", there is no need to select colors, but if the measurement type is "color spatial contrast sensitivity", two colors for discrimination also need to be selected. One of the colors is used as the background color, and the other color is used as the target color to be discriminated. The visual stimulus used in the measurement is a mixture of the background color and the target color in different proportions (the ratio of the background color to the target color ranges from 100% to 0%). Since the colors that can be individually displayed by common display devices are all red, green, and blue, the background color and the target color can be arbitrarily selected from the three colors of red, green, and blue. Preferably, the background color can be selected as red, and the target color can be selected as green.

[0091] Optionally, the parameter acquisition module can also acquire parameters related to the visual stimulus attributes, including the size of the stimulus. The size of the stimulus is mostly marked by the diameter, and the unit is the visual angle. The macular area of the human eye generally does not exceed 6 degrees of visual angle, so the value range of the stimulus size is generally 2.5 - 6.0 degrees of visual angle. In addition, in actual applications, to reduce the difference between the stimulus edge and the background, the stimulus edge is often blurred using a specific algorithm. For the stimulus after edge blurring, it is necessary to ensure that the size of the non-edge area that has not been blurred meets the test requirements. Specifically, the stimulus size can be selected as 5.5 degrees of visual angle, where the size of the blurred edge is 0.75×2 = 1.50 degrees of visual angle, and the non-edge area that has not been blurred is 5.5 - 1.5 = 4.0 degrees of visual angle.

[0092] Optionally, the parameters related to the visual stimulus properties obtained by the parameter acquisition module also include the presentation time of the stimulus. To ensure that the measurement results can reflect the function of the central area of the visual field of the measured individual and avoid the visual line of sight of the measured individual drifting during the test, the stimulus presentation time should not be too long, generally between 50 and 250 milliseconds. Preferably, the presentation time is 150 milliseconds.

[0093] Optionally, the parameters related to the visual stimulus attributes obtained by the parameter acquisition module also include auxiliary features related to stimulus identification. When the measured individual identifies the stimulus, it is mainly based on contrast information, but cannot directly feedback the perception of contrast. Therefore, the stimulus should contain auxiliary features, usually shape (such as Figure 3 3rd row in the left column, and rows 1-2 in the right column), direction or orientation (such as Figure 3 In the test, there are two or more attribute options for the individual being measured to identify. Generally, the stimulus is a directional feature. For example, Figure 3 The grating stimuli displayed in the 1st and 2nd rows of the left column in the figure have two position combinations: "90 degrees and 0 degrees" and "45 degrees and 135 degrees". The difference between the two options in the combination is 90 degrees. Figure 3 The third row of the right column displays letter stimuli, one normal and one inverted, which is equivalent to the direction combination of "0 degrees and 180 degrees", and the difference between the two options in the combination is 180 degrees.

[0094] After obtaining the necessary parameters, the visual stimulus generation module can generate non-color visual stimuli or color visual stimuli for measurement based on the obtained parameters and the system built-in parameters. The non-color visual stimuli include non-color grating stimuli (such as Figure 3 1-2 rows in the left column) and non-color graphic stimuli ( Figure 3 It should be noted that when measuring spatial contrast sensitivity, it is more standard to use non-color grating stimulation, because non-color grating stimulation is more consistent with the receptive field characteristics of the visual system cortical neurons, but simple graphics drawn with uniform lines can also achieve good results. More importantly, compared with non-color grating stimulation, non-color graphic stimulation has a more intuitive meaning and is easy to identify, which is conducive to infant or animal testing.

[0095] Non-color visual stimuli are presented on a uniform gray background, and part or all of the stimulus has a different brightness from the background, such as Figure 3 The recognition difficulty of non-color visual stimuli is determined by the brightness contrast of non-color visual stimuli (C l), and the luminance contrast of the achromatic visual stimulus can be the luminance contrast of the achromatic grating stimulus or the luminance contrast of the achromatic graphic stimulus.

[0096] The achromatic grating stimulus is the most common and can be constructed according to the following function:

[0097] ;

[0098] where l(x, y) represents the luminance of the point with coordinates (x, y) on the stimulus image, and L mean is the average background luminance, C l is the luminance contrast of the achromatic grating stimulus; f is the spatial frequency to be measured; DPD is the visual angle occupied by each point in the stimulus image, in degrees per point; θ is the grating orientation (used for auxiliary features related to stimulus identification), and φ is the grating phase. Preferably, L mean takes 0.5, and θ takes π / 4 or 3π / 4.

[0099] The luminance contrast of the achromatic grating stimulus is defined as:

[0100] ;

[0101] where C l represents the luminance contrast of the achromatic grating stimulus, represents the highest luminance of the achromatic grating stimulus, represents the lowest luminance of the achromatic grating stimulus.

[0102] When constructing the achromatic graphic stimulus, the properties of the auxiliary features can be set using a method similar to the grating orientation. For example, one is normal and the other is rotated or inverted. However, the more commonly used way to set the properties of the auxiliary features for text stimuli is shape. For example, Figure 3 the "O" and "Q" shown in the 3rd row of the left vertical column in

[0103] When constructing the achromatic graphic stimulus, the background should be white, and the graphic color should be selected as black or gray. The luminance of each part of the graphic should be kept consistent. At this time, the luminance contrast Cl of the achromatic graphic stimulus is defined as:

[0104] ;

[0105] where l pattern represents the luminance of the achromatic graphic stimulus, and L mean is the average background luminance, and abs(·) is the absolute value function;

[0106] The achromatic graphic stimulus is a stimulus image drawn with achromatic lines of uniform thickness. When constructing the achromatic graphic stimulus, it should be ensured that the thickness of the lines for drawing the graphic is consistent and meets the following requirements:

[0107] ;

[0108] Among them, f is the spatial frequency to be measured, with the unit of cycle / degree; DPD is the visual angle occupied by each point in the stimulus image, with the unit of degree / point.

[0109] If the thicknesses of the strokes that make up the text stimulus are inconsistent (such as Figure 3 the 3rd row in the right vertical column in ), it means that the text stimulus contains multiple different spatial frequencies. Even if all the included spatial frequencies are the spatial frequencies to be measured, such a stimulus cannot be used in the measurement. In other words, each visual stimulus image used in the measurement can only contain 1 spatial frequency to be measured and cannot contain other spatial frequencies.

[0110] Similar to non-color visual stimuli, color visual stimuli include color graphic stimuli and color grating stimuli, and color visual stimuli are also presented on a unified background. However, different from non-color visual stimuli, color visual stimuli and the background have exactly the same brightness but present different colors, such as Figure 3 shown in the 1st row in the right vertical column in . The background only contains the first color, and the color of the color visual stimulus is formed by mixing the first color and the second color. The difficulty of identifying the color visual stimulus is indicated by the color contrast (C c ) of the color visual stimulus. The color contrast of the color visual stimulus can be the color contrast of the color graphic stimulus or the color contrast of the color grating stimulus. Preferably, the first color is red and the second color is green.

[0111] Similar to non-color graphic stimuli, color graphic stimuli are also stimulus images drawn with uniformly thick lines. When drawing, the following requirements should be met:

[0112] ;

[0113] ;

[0114] ;

[0115] Among them, f is the spatial frequency to be measured, with the unit of cycle / degree; DPD is the visual angle occupied by each point in the stimulus image, with the unit of degree / point; C c is the color contrast of the color graphic stimulus: L mean，color1 represents the background brightness, l pattern，color1 represents the brightness corresponding to the first color in the color graphic stimulus, and l pattern，color2 represents the brightness corresponding to the second color in the color graphic stimulus;

[0116] The color grating stimulus is generated according to the following formula:

[0117] ;

[0118] ;

[0119] ;

[0120] Among them, l(x, y) represents the brightness of the point with coordinates (x, y) on the stimulus image, and l(x, y) colorl represents the brightness corresponding to the first color in the brightness of this point, and l(x, y) color2 represents the brightness corresponding to the second color in the brightness of this point, L mean，color1 represents the background brightness with the first color; C c is the color contrast of the color raster stimulus; f is the spatial frequency to be measured, DPD is the visual angle occupied by each point in the stimulus image, in degrees / point; θ is the grating orientation, and φ is the grating phase. Preferably, L mean，color1 takes 0.5, and θ takes π / 4 or 3π / 4.

[0121] It should be emphasized that regardless of whether it is a non-color visual stimulus or a color visual stimulus, the stimulus size is related to the pixel size of the display device and the test distance. The formula is:

[0122] ;

[0123] Among them, DPD is the visual angle occupied by each point in the stimulus image, in degrees / point; DotSize is the actual size of each point in the stimulus image (i.e., the pixel size of the display device), in centimeters; distance is the test distance.

[0124] Therefore, to ensure the accuracy and effectiveness of the measurement results, the measurement distance should be ensured not to change during the measurement process. Optionally, the human-computer interaction module may include a jaw rest and a distance evaluation unit. The specific work of the jaw rest and the distance evaluation unit is as follows: The jaw rest is used to fix the lower jaw of the individual being measured during the measurement process. During the measurement process, the distance between the screen presenting the visual stimulus and the jaw rest is evaluated in real time through a distance sensor. When the relative difference between the evaluated distance and the specified measurement distance exceeds 5% of the specified measurement distance, a voice prompt of "correct the distance" is given.

[0125] In addition, to ensure that the brightness value of the visual stimulus actually presented to the individual being measured accurately reaches the theoretical calculated value, the human-computer interaction module also includes a brightness evaluation and conversion unit, which can regularly evaluate the brightness distribution of the display device at different hardware brightness levels, and accordingly convert the theoretical brightness value of the visual stimulus required to be presented into a hardware brightness level value that meets the requirements.

[0126] It should be noted that due to the variability of the display device's hardware settings (such as the parameter options of "brightness", "contrast", and "Gamma" adjusted through buttons on the display), and the impact of hardware aging during use, the brightness distribution of the display device at different hardware brightness levels will inevitably change continuously during use. Therefore, regular evaluation of the display device is a necessary prerequisite to ensure the display accuracy of visual stimuli.

[0127] The hardware brightness level of a display device is usually determined by the display bit depth. When the display bit depth is 8 bits, the hardware brightness level of the display device is divided into 2^8 = 256 levels; when the display bit depth is 10 bits, the hardware brightness level of the display device is divided into 2^10 = 1024 levels. To put it more intuitively, when the display bit depth is 8 bits, the 256 hardware brightness levels correspond to the brightness in 256 cases such as "r = 0, g = 0, b = 0", "r = 1, g = 1, b = 1" up to "r = 255, g = 255, b = 255" in the color palette; when the display bit depth is 10 bits, the 1024 hardware brightness levels correspond to the brightness in 1024 cases such as "r = 0, g = 0, b = 0", "r = 1, g = 1, b = 1" up to "r = 1023, g = 1023, b = 1023" in the color palette.

[0128] It is worth mentioning that without special treatment, the default setting used by the display device when displaying images is that "there is a linear relationship between the rgb value and the brightness". In other words, the display device defaults that the actual brightness corresponding to "r = 200, g = 200, b = 200" is twice the actual brightness corresponding to "r = 100, g = 100, b = 100". However, this is not the case. For the vast majority of display devices, the actual brightness corresponding to "r = 200, g = 200, b = 200" is more than twice the actual brightness corresponding to "r = 100, g = 100, b = 100". The relationship between the actual display brightness values corresponding to the 256 hardware brightness levels and the rgb values often shows a power function relationship, and in a few cases, it is a more complex curve relationship, such as an S-shaped curve. Such a setting is conducive to highlighting more brightness levels when presenting images, but is not conducive to precisely controlling the presentation brightness of visual stimuli.

[0129] Therefore, this system cannot use the default settings of the display device to present visual stimuli. To improve the applicable range and accuracy, this system uses a piecewise power function to evaluate the corresponding relationship between the hardware brightness level and the actual brightness.

[0130] After regular measurement and evaluation, the functional relationship between the "theoretical brightness value of the visual stimulus to be presented" and the "hardware brightness level value meeting the requirements" can be obtained or updated. On this basis, the theoretical brightness value of the visual stimulus required for each pixel of the visual stimulus generated by the visual stimulus generation module can be converted into the hardware brightness level value meeting the requirements and presented accurately.

[0131] The specific working steps of the brightness evaluation and conversion unit are as follows:

[0132] S1-1. Under the condition of the fixed hardware settings of the display device, measure and record the actual screen brightness at each hardware brightness level one by one according to the hardware brightness level prompted by the display device bit depth;

[0133] S1-2. Use the following formula to perform data fitting on the measured data:

[0134] ;

[0135] where l is the measured screen brightness, x is the hardware brightness level, a1, a2, b1, b2, and BP are all fitting parameters; min(·) is the minimum value function;

[0136] S1-3. When presenting the visual stimulus, convert the theoretical brightness value of the visual stimulus transmitted by the visual stimulus generation module into the hardware brightness level that should be used during actual presentation according to the formula in S1-2.

[0137] It should be noted that the hardware brightness level that should be used during actual presentation calculated according to the formula in S1-2 is often a non-integer, but the hardware brightness level actually used by the display device must be a positive integer. Therefore, in actual operation, the rounding method is usually used to round to the nearest integer. From this perspective, there is often a certain deviation between the actually presented brightness and the theoretically calculated value. To effectively reduce the deviation, the display bit depth of the display device should be above 10 bits, and the higher the better.

[0138] When generating visual stimuli, it is also necessary to consider the initial contrast value corresponding to the spatial frequency to be measured. When introducing the minimum change unit of contrast earlier, the necessity of shortening "Phase 1" in the testing process has been explained. From this perspective, it seems that the closer the initial difficulty is to the actual functional level of the individual being measured, the shorter "Phase 1" will be, which is more conducive to improving the accuracy of the measurement results. However, a lower initial difficulty that is far from the actual functional level of the individual being measured is beneficial for the individual being measured to identify the stimuli at the beginning of the measurement and quickly get familiar with the measurement process, avoiding mistakes caused by unfamiliar operations and reducing the accuracy of the measurement results. Therefore, the most appropriate choice is to appropriately adjust the initial difficulty of contrast so that it is relatively close rather than absolutely close to the actual functional level of the individual being measured. Optionally, the initial contrast value can be determined as follows: If the spatial frequency to be measured is less than 4 cycles / degree, the initial contrast value is set to 0.1; if the spatial frequency to be measured is greater than or equal to 4 cycles / degree but less than 16 cycles / degree, the initial contrast value is set to 0.20; if the spatial frequency to be measured is greater than or equal to 16 cycles / degree, the initial contrast value is set to 0.60.

[0139] After the visual stimuli are generated, they can be presented to the individual being measured. After obtaining the identification situation of the individual being measured for the stimuli, the next stimulus is presented. This cycle continues until all the trials are completed.

[0140] When presenting the stimuli, it is necessary to pay attention to the order rules for presenting visual stimuli with different spatial frequency information to be measured. Generally, there are two presentation rules: "sequential presentation" and "alternating presentation". Under the "sequential presentation" rule, the system will execute all the trials required at a certain spatial frequency to be measured in a concentrated manner, and then execute all the trials required at the next spatial frequency to be measured in a concentrated manner after completion. This is repeated until all the trials at all spatial frequencies to be measured are completed. Under the "alternating presentation" rule, the system will mix all the trials required at all spatial frequencies to be measured together and then execute them in the mixed order one by one. Existing research data show that the presentation rule has a certain impact on the measurement results. Under the same conditions, the sensitivity measured under the "sequential presentation" rule is better than that measured under the "alternating presentation" rule. That is, the position of the spatial contrast sensitivity curve measured under the "sequential presentation" rule in the coordinate space is higher than that obtained under the "alternating presentation" rule.

[0141] The selection of the presentation rule does not affect the change rule of the stimulus difficulty at a single spatial frequency to be measured. At a single spatial frequency to be measured, the difficulty level of the stimulus (i.e., the contrast level corresponding to the spatial frequency to be measured) will change continuously during the measurement process. The change rule is the core content of the measurement process control. Based on the response of the individual being measured to the visual stimulus, the specific steps to continuously adjust the contrast of the visual stimulus presented to the individual being measured are as follows:

[0142] S2-1. If the current trial is the first trial at the spatial frequency to be measured, the stimulus contrast uses the default value;

[0143] S2-2. If in the previous trial, the individual being measured correctly identified the stimulus, then in the next trial presenting the visual stimulus at the same spatial frequency to be measured, the contrast of the visual stimulus is reduced by 1 minimum change unit; if the identification result was incorrect in the previous trial, then in the next trial presenting the visual stimulus at the same spatial frequency to be measured, the contrast of the visual stimulus is increased by the first specified number of minimum change units; where the first specified number is a positive integer greater than 1; preferably, the first specified number is 3;

[0144] S2-3. At a certain spatial frequency to be measured, if the number of trials presented to the individual being measured has reached the set maximum test amount, or the contrast of the visual stimulus presented to the individual being measured fluctuates repeatedly within the first specified range, or the contrast of the visual stimulus has reached the upper and lower limits of the measured contrast range continuously 3 times or cumulatively 5 times, then terminate the test at this spatial frequency and no longer adjust the contrast of the visual stimulus at this spatial frequency. Preferably, the first specified range is 5 minimum change units of contrast.

[0145] It should be noted that due to the hardware limitations of the display device, there are upper and lower limits for the actually measurable contrast. If the function of the individual being measured is too good or too bad, exceeding the measurable range of the system, it will cause the contrast of the visual stimulus adjusted by the process control module to always fluctuate near the upper and lower limits of the measured contrast range, resulting in situations such as "the contrast of the visual stimulus has reached the upper and lower limits of the measured contrast range continuously 3 times or cumulatively 5 times" mentioned in S2-3. Therefore, it is meaningless to continue the measurement at this time and it should be terminated in a timely manner.

[0146] Figure 4Shows part of the test process at a single spatial frequency to be measured. The black or red circles in the figure represent each trial. The abscissa represents the sequential position of the trial among all trials at this spatial frequency, and the ordinate represents the contrast level corresponding to the spatial frequency to be measured in the stimulus presented in this trial. The difference between adjacent contrast levels on the ordinate is 3 dB. The "√" above and "×" below the circles in the figure indicate the identification situation of the individual being measured for the stimulus in this trial. It can be seen from the figure that when the individual being measured identifies correctly (i.e., "√"), the difficulty level in the next trial is increased by 1 level, that is, the contrast level is decreased by 1 level (for example, based on 0.020, it is decreased by 3 dB and becomes 0.020 / 10ˆ(3 / 20) = 0.014); when the individual being measured identifies incorrectly (i.e., "×"), the difficulty level in the next trial is decreased by 3 levels, that is, the contrast level is increased by 3 levels (for example, based on 0.020, it is increased by 3×3 = 9 dB and becomes 0.020×10ˆ(3*3 / 20) = 0.056).

[0147] The above process control rules will actually necessarily lead to a phenomenon. That is, if the performance of the individual being measured is stable and not affected by any non-sensory factors (such as fatigue, proficiency, rewards and punishments, etc.), and the test volume at a single spatial frequency to be measured is large enough, the contrast presented to the individual being measured in the middle and late stages of the test will necessarily fluctuate around a certain specific level (refer to the situation after the 14th trial in Figure 4 . Even if there is an occasional deviation from this level (refer to the 30th trial in Figure 4 ), it will be pulled back by the above process rules (refer to the situation of the 31st - 38th trials in Figure 4 ). This specific level is actually the true functional level of the individual being measured. For example, Figure 4 the true level of the individual being measured should be between contrast levels 3 and 6.

[0148] Therefore, Figure 4 the entire test process in

[0149] can be divided into two stages. The process from the start of the test (the 1st trial) to the first change in the identification situation of the individual being measured for the stimulus (the 17th trial) belongs to stage one, and the subsequent ones all belong to stage two. Within stage one, the stimulus difficulty level is gradually adjusted from the initial level to near the level corresponding to the true functional level of the individual being measured. This is the preparatory stage for obtaining effective measurement data. Within stage two, the stimulus difficulty level fluctuates near the true functional level of the individual being measured. This is the stage for truly obtaining effective measurement data.

[0149] Theoretically, it can be predicted that within stage two, when the presented stimulus contrast level reaches the true level of the individual being measured, the following relationship should hold:

[0150] ;

[0151] Wherein, is the probability that when the contrast level reaches the true level of the individual being measured, the individual being measured can correctly perceive the stimulus when it appears, is the degree of reduction of the contrast level in the next trial after the individual being measured correctly perceives and gives feedback, is the probability that when the contrast level reaches the true level of the individual being measured, the individual being measured fails to correctly perceive the stimulus when it appears, is the degree of increase of the contrast level in the next trial when the individual being measured fails to correctly perceive and give feedback.

[0152] Combined with the aforementioned rules, "in a trial, if the result of the individual being measured's identification of the stimulus is correct, then in the next trial of presenting the visual stimulus with the same spatial frequency to be measured, the contrast corresponding to the spatial frequency to be measured is reduced by 1 minimum change unit; if the identification result is incorrect, then in the next trial of presenting the visual stimulus with the same spatial frequency to be measured, the contrast is increased by the first specified quantity (n) of minimum change units", the following formula can be derived p correct = n x p incorrect According to p correct + p incorrect = 100% established fact, it can be further derived that p correct = n / ( n + 1). Specifically, when n takes 2, p correct = 66.7%; when n takes 3, p correct = 75.0%; when n takes 4, p correct = 80.0%; when n takes 5, p correct = 83.3%. Therefore, theoretically speaking, when n takes different values and is combined with a sufficient amount of tests, the thresholds at multiple different sites on the psychophysical measurement curve can be obtained through the above process control method, and these sites are all located in the relatively steep middle section of the S-shaped measurement curve.

[0153] Of course, due to the limitations of measurement accuracy (the minimum change unit of contrast) and the existence of various errors, it is very difficult for the contrast level of the presented stimulus in actual measurement to exactly reach the true level of the measured individual. Generally, it fluctuates repeatedly around the true level. Therefore, in actual measurement, statistical methods can be used to take the arithmetic mean of the contrast values corresponding to all the data points that "change from correct identification to incorrect identification" ( Figure 4 represented by a red "×" in Figure 4 and the data points that "change from incorrect identification to correct identification" (

[0154] represented by a red "√" in

[0155] ). Based on this, the true level of the measured individual can be inferred. According to statistical laws, the more such data points there are, the closer the arithmetic mean of the contrast values corresponding to these data points is to the true level of the measured individual. That is, the larger the test volume, the higher the accuracy of the analysis result. Generally speaking, the above process control method, data analysis rules, and sufficient test volume can ensure the accuracy of the measurement results. Among them, the process control method can theoretically ensure the positioning of the test results on the S-shaped measurement curve, while the data analysis rules and sufficient test volume can ensure that the actual operation / analysis results approach the theoretical value statistically and meet the operational requirements of practical applications. It is worth mentioning that the control of measurement accuracy in this system can be achieved by adjusting the minimum change unit of contrast (i.e., the size of the difference between adjacent levels of stimulus intensity), which has no direct connection with the process control method, data analysis rules, and test volume. Therefore, the control of measurement accuracy and the accuracy of measurement results in this system are independent and separated from each other. However, this cannot be achieved in existing spatial contrast sensitivity measurement devices or systems. Existing spatial contrast sensitivity measurement devices or systems cannot take into account both measurement accuracy and the accuracy of measurement results. If the difference between adjacent levels is reduced, the measurement accuracy can be improved, but it will shake the default assumption that "at the highest difficulty (this difficulty is the final measurement result) that the measured individual can correctly identify in the measurement, the identification accuracy rate of the measured individual is 100%, and at the next higher difficulty, the identification accuracy rate decreases significantly", thereby reducing the accuracy of the measurement results; while if the difference between adjacent contrast levels is increased to ensure the validity of the default assumption, the measurement accuracy will be reduced.

[0156] During the measurement process, the system will record data. After the measurement is completed, the system will perform data analysis, analyze and determine the sensitivity of the measured individual at multiple spatial frequencies to be measured, and draw a spatial contrast sensitivity curve. The specific steps include:

[0157] S3-1. Based on the recorded data, select a spatial frequency to be measured. According to the trial order that occurred during the actual measurement at this spatial frequency, list the visual stimulus contrast used in each trial, as well as the correct / incorrect situation of the measured individual's identification of the visual stimulus.

[0158] S3-2. Based on the list sorted out in S3-1, select the visual stimulus contrast at the point where the change trend of the visual stimulus contrast changes during the measurement process, and record them all as C. cri ;

[0159] S3-3. If the number of C at this spatial frequency cri is less than the second specified number, end the analysis and prompt "Unable to determine the threshold, remeasurement should be carried out"; otherwise, proceed to step S3-4; preferably, the second specified number is 10.

[0160] S3-4. If the difference between the maximum value and the minimum value among all C cri does not exceed the third specified number of minimum contrast change units, determine the reciprocal of the arithmetic mean of all C cri as the contrast sensitivity of the measured individual at this spatial frequency; otherwise, proceed to step S3-5; preferably, the third specified number is 5.

[0161] S3-5. Among all C cri , in chronological order, remove the first 3 or the first 4 C cri so that the number of the remaining C cri is an even number, and then take the reciprocal of the arithmetic mean of all the remaining C cri , and the result is the contrast sensitivity of the measured individual at this spatial frequency.

[0162] S3-6. Sequentially execute the steps in S3-1 to S3-5 at all spatial frequencies to be measured, and obtain the contrast sensitivity of the measured individual at all spatial frequencies to be measured.

[0163] S3-7. Based on the contrast sensitivity of the measured individual at all spatial frequencies to be measured obtained in S3-6, on a double-logarithmic coordinate axis, use the spatial frequency to be measured as the abscissa and the contrast sensitivity as the ordinate to plot a spatial contrast sensitivity curve graph.

[0164] The C mentioned in S3-2 cri , that is, Figure 4 the visual stimulus contrast at the red circle in cri . In addition, for the analysis method of taking the arithmetic mean of Ccri , both are less reliable than the subsequent C cri . Therefore, on the premise of ensuring that there are a sufficient number of C cri and C cri have a large difference, several of the previous C can be removed in S3-5 cri , so as to improve the accuracy of the analysis results.

[0165] In addition, the purpose of "removing the first 3 or the first 4 C cri , so that the remaining C cri is an even number" is also to ensure that the number of two different types of data points, namely the data points "changing from correct identification to incorrect identification" and the data points "changing from incorrect identification to correct identification", in the remaining C cri is the same, so as to provide the accuracy of the analysis results.

[0166] Based on the step descriptions of S3-1 – S3-7, it can be understood that if during the measurement of a certain spatial frequency to be measured, the C cri that appears always fluctuates within the first specified range and has accumulated to the fourth specified quantity, then even if the number of trials at this spatial frequency has not reached the maximum test amount, the test at this spatial frequency can be terminated in advance, and the existing C cri can be used to calculate the sensitivity of the individual being measured at this spatial frequency. Generally, the value range of the fourth specified quantity is 6 to 20. Preferably, the fourth specified quantity is 8.

[0167] It should be noted that terminating the test in advance under the above conditions is essentially to effectively shorten the measurement time on the basis of ensuring the reliability of the measurement results. Therefore, when the individual being measured is an infant with difficulty in concentrating attention for a long time or an animal that cannot communicate effectively, the above settings help to complete the test while ensuring the measurement effectiveness.

[0168] The present invention can not only complete the measurement of luminance spatial contrast sensitivity, but also measure color spatial contrast sensitivity, and overcomes the shortcomings of traditional measurement systems. It can adjust the measurement range and measurement accuracy according to the needs of actual applications, has strong universality, can take into account both measurement accuracy and accuracy through the design of the measurement and analysis process, and can also reduce the use difficulty through the application of graphic stimuli. It is applicable to the evaluation of infant or animal functions and has a broader application prospect.

[0169] The above are only specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent replacements or modifications made on the basis of the present invention to achieve basically the same technical effects are all covered by the protection scope of the present invention.

Claims

1. A measurement system for spatial contrast sensitivity curve, characterized in that Including: A parameter acquisition module that acquires a measurement type and measurement parameters. The measurement type includes luminance spatial contrast sensitivity and color spatial contrast sensitivity. General measurement parameters include multiple spatial frequencies to be measured, the maximum test quantity at a single spatial frequency to be measured, and the minimum change unit of the contrast corresponding to the spatial frequency to be measured. If the measurement type is color spatial contrast sensitivity, two colors also need to be selected from red, green, and blue, where the first color is the color used as the background, and the first color and the second color are the colors used as stimuli. A visual stimulus generation module that generates visual stimuli for measurement based on the parameters acquired by the parameter acquisition module and the built-in parameters of the system. The visual stimuli include achromatic visual stimuli or chromatic visual stimuli. A human-computer interaction module that presents the generated visual stimuli to the individual to be measured and obtains the correct / wrong situation of the individual to be measured's identification of the visual stimuli. The human-computer interaction module includes a luminance evaluation and conversion unit. The luminance evaluation and conversion unit regularly evaluates the luminance distribution of the display device at different hardware luminance levels and converts the theoretical luminance value of the visual stimulus to be presented into a hardware luminance level value that meets the requirements. The specific working steps of the luminance evaluation and conversion unit are as follows: S1-1. With the hardware settings of the display device fixed, evaluate and record the actual screen luminance at each hardware luminance level one by one according to the hardware luminance levels prompted by the display device bit depth. S1-2. Use the following formula to perform data fitting on the evaluation data: where l is the actual screen luminance; x is the hardware luminance level; a1, a2, b1, b2, and BP are all fitting parameters; min(·) is the minimum value function. S1-3. When presenting the visual stimulus, convert the theoretical luminance value required at each pixel point of the visual stimulus transmitted by the visual stimulus generation module into the hardware luminance level value that should be used at each pixel point during actual presentation according to the formula in S1-2. A process control module that continuously adjusts the contrast of the visual stimulus presented to the individual to be measured based on the response of the individual to be measured to the visual stimulus. The visual stimulus contrast includes the luminance contrast of the achromatic visual stimulus or the color contrast of the chromatic visual stimulus until the identification situation of the individual to be measured for the visual stimulus meets the specified requirements. The specific steps are as follows: S2-1. If the current trial is the first trial at the spatial frequency to be measured, the visual stimulus contrast uses the default value. S2-2. If in the previous trial, the result of the individual to be measured's identification of the visual stimulus is correct, then in the next trial of presenting the visual stimulus at the same spatial frequency to be measured, the visual stimulus contrast is reduced by 1 minimum change unit. If the identification result in the previous trial is wrong, then in the next trial of presenting the visual stimulus at the same spatial frequency to be measured, the visual stimulus contrast is increased by the first specified number of minimum change units. Among them, the first specified number is a positive integer greater than 1. S2-3. At the current spatial frequency to be measured, if the number of trials presented to the individual to be measured has reached the set maximum test amount, or the visual stimulus contrast presented to the individual to be measured fluctuates repeatedly within the first specified range, or the visual stimulus contrast has reached the upper and lower limits of the measured range of the visual stimulus contrast for 3 consecutive times or a cumulative of 5 times, then terminate the test at this spatial frequency and no longer adjust the contrast of the visual stimulus at this spatial frequency; The data recording and analysis module records all visual stimulus contrasts during the measurement process, as well as the response data of the individual to be measured, analyzes and determines the sensitivity of the individual to be measured at multiple spatial frequencies to be measured, and based on this, draws a spatial contrast sensitivity curve. The spatial contrast sensitivity curve includes a luminance spatial contrast sensitivity curve or a color spatial contrast sensitivity curve; The specific steps for drawing the spatial contrast sensitivity curve are as follows: S3-1. Based on the recorded data, at each spatial frequency, sequentially find the value at the point where the change trend of the visual stimulus contrast changes, and denote it as C cri ; S3-2. If the number of C at any spatial frequency cri is less than the second specified number, end the analysis at this spatial frequency and prompt: Unable to determine the threshold, re-measurement is required; otherwise, based on all C at this spatial frequency cri , determine the contrast sensitivity of the measured individual at this spatial frequency. S3-3. Based on the contrast sensitivities at all spatial frequencies to be measured obtained in S3-2, on a double-logarithmic coordinate axis, with the spatial frequency to be measured as the abscissa and the contrast sensitivity as the ordinate, draw a spatial contrast sensitivity curve graph.

2. The measurement system of a spatial contrast sensitivity curve according to claim 1, wherein: The minimum change unit of the contrast corresponding to the spatial frequency to be measured has a value range of 0.5 to 6.0 dB, and different initial values are selected at different spatial frequencies to be measured, and then gradually becomes smaller as the measurement progresses.

3. The measurement system of a spatial contrast sensitivity curve according to claim 1, characterized in that: The parameter acquisition module also needs to acquire parameters related to the visual stimulus attributes, including the size, presentation time of the visual stimulus, and auxiliary features related to the visual stimulus identification. And there are two or more visual stimulus attribute options in the test for the individual to be measured to identify. The size of the visual stimulus is marked by the diameter, and the diameter size has a value range of 2.5 to 6.0 degrees of visual angle. The value range of the presentation time of the visual stimulus is 50 to 250 milliseconds. The auxiliary features related to the visual stimulus identification are shape, orientation or azimuth.

4. The measurement system of a spatial contrast sensitivity curve according to claim 1, characterized in that: The non-color visual stimuli include non-color graphic stimuli and non-color grating stimuli. The non-color visual stimuli are presented on a unified gray background, and part or all of the non-color visual stimuli have a brightness different from that of the background. The difficulty of identifying the non-color visual stimuli is indicated by the brightness contrast C of the non-color visual stimuli l for marking; The achromatic graphic stimulus is a stimulus image drawn with achromatic lines of uniform thickness, and the line thickness meets the following requirements: Where f is the spatial frequency to be measured, with the unit of cycle / degree; DPD is the visual angle occupied by each point in the stimulus image, with the unit of degree / point; Luminance contrast C of non-color graphic stimuli l is defined as: where l pattern represents the luminance of the achromatic graphic stimulus, L mean is the background average luminance, and abs(·) is the absolute value function; The achromatic grating stimulus is constructed according to the following function: where l(x, y) represents the luminance of the point with coordinates (x, y) on the stimulus image, and L mean is the average background luminance, and C l is the luminance contrast of the achromatic grating stimulus; f is the spatial frequency to be measured; DPD is the visual angle occupied by each point in the stimulus image, in degrees per point; θ is the grating orientation, and is the grating phase.

5. The measurement system of a spatial contrast sensitivity curve according to claim 1, characterized in that: The color visual stimuli include color graphic stimuli and color grating stimuli. The color visual stimuli are presented on a unified background. The color visual stimuli and the background have exactly the same brightness but different colors. The background only contains the first color, and the color of the color visual stimuli is a mixture of the first color and the second color. The difficulty level of identifying the color visual stimuli is indicated by the color contrast C of the color visual stimuli C for marking; The chromatic graphic stimulus is a stimulus image drawn with lines of uniform thickness, and when drawing, it should meet the following requirements: L mean,color1 ＝l pattern,color1 +l pattern，color2 Among them, f is the spatial frequency to be measured, with the unit of cycle / degree; DPD is the visual angle occupied by each point in the stimulus image, with the unit of degree / point; C C is the color contrast of the color graphic stimulus: L mean，color1 represents the background luminance, l pattern，color1 represents the luminance corresponding to the first color in the color graphic stimulus, l pattern，color2 represents the luminance corresponding to the second color in the color graphic stimulus; The chromatic grating stimulus is generated according to the following formula: l(x,y) = l(x, y) color1 + l(x, y) color2 Among them, l(x, y) represents the luminance of the point with coordinates (x, y) on the stimulus image, l(x, y) colorl represents the luminance corresponding to the first color in the luminance of this point, l(x, y) color2 represents the luminance corresponding to the second color in the luminance of this point, L mean , color1 represents the background luminance with the first color; C C is the color contrast of the color grating stimulus; f is the spatial frequency to be measured, DPD is the visual angle occupied by each point in the stimulus image, with the unit of degree / point; θ is the grating orientation, is the grating phase.

6. The measurement system of a spatial contrast sensitivity curve according to claim 1, wherein: The man-machine interaction module also includes a jaw support and distance evaluation unit. The specific working process of the jaw support and distance evaluation unit is as follows: The jaw support is used to fix the lower jaw of the individual to be measured during the measurement process. During the measurement process, the distance between the screen presenting the visual stimulus and the jaw support is evaluated in real time through a distance sensor. When the relative difference between the evaluated distance and the specified measurement distance exceeds 5% of the specified measurement distance, a voice prompt of "correct the distance" is given.

7. The measurement system of a spatial contrast sensitivity curve according to claim 1, characterized in that: In step S2-3, the visual stimulus contrast presented to the individual to be measured fluctuates repeatedly within a first specified range, specifically: taking the C obtained last time as a reference, a fourth specified number of Cs have been cumulatively obtained within the first specified range. cri The value range of the fourth specified number is 6 to 20. cri ​

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