RU2357648C1 - Method of detection of passband of spatial frequency channel of human vision system - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: invention pertains to medicine. The subject is exposed to light flitting, emitted by light emitting diodes with preset initial frequency. Light flitting frequency of the first diode remains unchanged, light flitting frequency of the second diode is increased presenting increment frequency, or decreased presenting decrement frequency. During the first stage of the measurements frequency of light flitting of the second light emitting diode is first continuously increased at the speed of 0.5 Hz/s, until the subject subjectively detects difference between the presented frequencies and registers thereat the first increment frequency of light flitting. Then frequency of light flitting of the second light emitting diode is continuously decreased at the speed of 0.25 Hz/s, until the subject detects the point, when presented light flittings do not differ and registers thereat the second increment frequency of light flitting. Thereafter frequency of light flitting of the second diode is discretely increased in increments of 0.1 Hz, till the subject registers differential threshold of the presented light flitting and registers the third increment frequency of light flitting. Threshold value is computed as the difference between the third increment and initial frequencies of light flitting. During the second stage of measurements having presented light flitting at the preset initial frequency, the latter is first continuously decreased at the same constant speed of 0.5 Hz/s, until the subject subjectively detects difference between the presented frequencies and registers thereat the first decrement frequency of light flitting. Then frequencies of light flitting of the second diode are increased at the same constant speed of 0.25 Hz/s until the subject detects the point when the presented light flittings do not differ and registers thereat the second decrement frequency of light flitting. Thereafter frequencies of light flitting of the second diode are discretely decreased at increments of 0.1 Hz until the subject detects the differential threshold of the presented light flitting. Differential threshold value is computed as the difference between the third decrement and initial frequencies of light flitting. Pass band of the spatial frequency channel is defined as the arithmetic mean value of differential threshold values of light flitting frequencies, computed during the first and the second stages of the measurements.

EFFECT: method makes it possible to detect pass band of the spatial frequency channel of the vision system by presenting two flitting lights using light emitting diodes to the subject.

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Description

The invention relates to medicine and is intended to determine the bandwidth of the spatial-frequency channel of the visual system.

It is known that at first the visual system was considered as one spatial filter. It was assumed that the sensitivity of the visual system to various spatial frequencies is determined by the transfer function of this filter [1]. Campbell and Robson first suggested that the visual system consists of many parallel filter channels, each of which is sensitive to certain spatial frequencies, that is, has its own bandwidth [2].

Blackmore and Campbell's experiments are known, which established the existence of spatial-frequency channels in the visual system. They showed that adaptation to a sinusoidal lattice of a certain frequency causes a decrease in sensitivity only to this frequency and its immediate surroundings. Subtracting from the transfer function of the visual system the same function obtained after adapting to one frequency, the authors obtained the spatial-frequency characteristic of the channel tuned to this frequency [3].

Spatial-frequency channels with their bandwidth occupy a certain area in the visible range. The bandwidths of the spatial-frequency channels of the entire visual system cover the entire visible spatial-frequency range [4].

It is known to determine the bandwidth of the spatial frequency channel of the visual system using thin light and dark bands, as well as gratings of different spatial frequencies with a sinusoidal distribution of illumination. Moreover, the spatial frequency of the lattice is understood as the number of periods of the brightness distribution per degree of the field of view [4, 5].

It is known to determine the bandwidth of the spatial frequency channel of the visual system by forming sinusoidal gratings on the screen of cathode ray tubes [2, 6], as well as using personal computers [7].

The disadvantage of this method is the low accuracy of determining the bandwidth of the spatial frequency channel of the visual system.

Closest to the technical nature of the present invention is a method for determining the bandwidth of the spatial-frequency channel of the visual system by presenting the subject with light flicker, which consists in the fact that the subject is presented with flicker light with a given initial frequency, for example 10 Hz, then light flicker with increased compared with the initial - incremental or reduced compared to the initial - decrement frequencies, while first they show light flickers with continuous increasing incremental or continuously decreasing decreasing frequencies, then alternately with a predetermined constant period equal to, for example, 1 s, light flickers with initial and incremental or initial and decrement frequencies, and at the first stage of measurements after presentation of light flickers with a given initial frequency at the beginning continuously increasing with a given constant speed, for example 0.5 Hz / s, the incremental frequency of light flicker, until the subject determines the subjectively the difference between the initial th and incremental frequencies and will not fix at this moment the first incremental frequency of light flickers, then they present alternately with a given constant period light flickers with an initial frequency and decreasing during presentation with a given constant speed, for example 0.25 Hz / s, incremental frequency to those until the subject determines when the alternately presented light flickers with the initial and incremental frequencies do not differ and does not fix at this moment the second incremental frequency of light flickers , after this, light flickers are presented alternately with a predetermined constant period with an initial frequency and increasing at the moment of presentation beginning discretely with a given step, for example 0.1 Hz, incremental frequency until the subject determines the threshold for distinguishing between alternating light flickers from the initial and incremental frequencies and will not fix at this moment the third incremental frequency of light flickers, the threshold value is calculated as the difference between the third incremental and initial frequencies of light m flickering, at the second stage of measurements after the presentation of light flickers with the same predetermined - initial - frequency, at first they continuously decrease at the same predetermined constant speed 0.5 Hz / s the decrement frequency of the light flickers, until the subject determines the subjectively the difference between the initial and decrement frequencies and at this moment it will not fix the first decrement frequency of light flickers, then the light flickers are presented alternately with a given constant period with an initial frequency and increasing during presentation I with the same predetermined constant speed of 0.25 Hz / s decrement frequency until the subject determines when the alternately presented light flickers with the initial and decrement frequencies do not differ and does not fix at this moment the second decrement frequency of light flickers, after that present alternately with a predetermined constant period light flickers with an initial frequency and decreasing at the moment of presentation beginning discretely with the same predetermined step of 0.1 Hz decrement frequency until the subject is about it determines the threshold for distinguishing alternately presented light flickers with initial and decrement frequencies and does not fix the third decrement frequency of light flickers at this moment, the threshold value is calculated as the absolute difference between the third decrement and initial frequencies of light flickers, the passband of the spatial frequency channel is determined as the arithmetic mean thresholds for distinguishing the frequencies of light flickers calculated at the first and second stages of measurements [8].

The disadvantage of this method is the low accuracy of determining the bandwidth of the spatial frequency channel of the visual system, due to the need to use memory functions, in particular, access to short-term logical-semantic memory.

The technical result of the proposed method for determining the bandwidth of the spatial frequency channel of the visual system is to increase the accuracy of the assessment.

The technical result is achieved by the fact that the test subject is presented with light flickers with a predetermined initial frequency in the visible frequency range, and it is new that the initial frequency is presented simultaneously using two LEDs, the frequency of light flickers of the first LED is not changed, the frequency of light flickers of the second LED is increased by presenting incremental frequency, or decrease by presenting the decrement frequency in the first measurement stage after the presentation of light flickers with a given initial h frequency, the light flicker frequency of the second LED is first continuously increased at a constant speed of 0.5 Hz / s, until the subject determines subjectively the difference between the initial and incremental frequencies presented and fixes the first incremental light flicker frequency at that moment, then the light flicker frequency of the second LED is reduced with a constant speed of 0.25 Hz / s until the subject determines when the flickering light presented with the initial and incremental frequencies does not differ and does not fix at this moment, it increases the second incremental frequency of light flickering, after which the frequency of light flicker of the second LED increases discretely with a step of 0.1 Hz until the subject determines the threshold for distinguishing the presented light flicker with the initial and incremental frequencies and fixes the third incremental frequency of light flickering, the threshold value is calculated as the difference between the third incremental and initial frequencies of light flickers, in the second measurement stage after the presentation of light flickers with a given the initial frequency, the frequency of light flicker of the second LED is first continuously reduced at the same constant speed of 0.5 Hz / s, until the subject determines subjectively the difference between the initial and decrement frequencies and fixes at this moment the first decrement frequency of light flicker, then the frequency of light flicker the second LED is increased at the same constant speed of 0.25 Hz / s until the subject determines when the presented light flicker with the initial and decrement frequencies they differ and will not fix at this moment the second decreasing frequency of light flickering, after that the frequency of light flickering of the second LED is reduced discretely with a step of 0.1 Hz until the subject determines the threshold for distinguishing the presented light flickering with initial and decrement frequencies and fixes the third decrement light flicker frequency, threshold value is calculated as the absolute difference between the third decrement and initial light flicker frequencies, spatial-often passband of the channel is determined as the arithmetic mean of the thresholds for distinguishing the frequencies of light flicker calculated in the first and second stages of measurement.

Figure 1 presents the timing diagrams of the change in the frequency of light flickering presented to the test subject in the first measurement stage, figure 2 - presented to the test subject in the second measurement stage.

The proposed method for determining the bandwidth of the spatial frequency channel of the visual system is as follows.

The test subject is presented with light flickers with the initial frequency F _n set in the visible frequency range, for example 10 Hz, simultaneously using two LEDs (Fig. 1, time interval 0-T ₁ ), the frequency of light flickers of the first LED does not change.

At the first stage of measurements, the frequency of light flickering of the second LED is first continuously increased at a constant speed of 0.5 Hz / s, until the subject determines subjectively the difference between the initial F _n and incremental F _and frequencies (Fig. 1, time interval T ₁ -T ₂ ) and will not fix at this moment the first incremental frequency of light flicker F _{and 1} (Fig. 1, time point T ₂ ), then the frequency of light flicker of the second LED is reduced at a constant speed of 0.25 Hz / s until the subject determines when presented by the emitted flickers with the initial F _n and incremental F _and frequencies do not differ (Fig. 1, the time interval T ₃ -T ₄ ), and will not fix at this moment the second incremental frequency of the light flickers F _{and 2} (Fig. 1, time instant T ₄ ) , after that, the frequency of light flicker of the second LED is increased discretely with a step of 0.1 Hz until the subject determines the threshold for distinguishing the presented light flicker with the initial F _n and incremental F _and frequencies (Fig. 1, time interval T ₅ -T ₆ ) and do not lock the third incremental frequency of light flashes F _{and 3} (f D.1, at time T _7). The value of the frequency discrimination threshold ΔF _{and is} calculated as the difference between the third incremental F and ₃ and the initial F _n light flicker frequencies according to the formula

ΔF _and = F and ₃ -F _n .

At the second stage of measurements, the frequency of light flickering of the second LED is first continuously reduced at the same constant speed of 0.5 Hz / s, until the subject determines subjectively the difference between the initial F _n and decrement F _d frequencies presented (Fig. 2, time interval T ₈ - T ₉ ) and will not fix at this moment the first decreasing frequency of light flickering F _d1 (Fig. 2, time point T ₉ ), then the frequency of light flickering of the second LED will increase at the same constant speed of 0.25 Hz / s until the subject will not determine when dyavlyaemye flashing light with the initial F _n and F _d decremental frequencies are not different (Figure 2, time interval T ₁₀ -T ₁₁₎ and do not lock at this point the second light flashes decremented frequency F _q2; (figure 2, time point T ₁₁ ), after that the frequency of light flickering of the second LED is reduced discretely in increments of 0.1 Hz until the subject determines the threshold for distinguishing the presented light flicker with the initial F _n and decrement F _d frequencies (Fig .2, the time interval T ₁₂ -T ₁₃ ) and will not fix the third decrement frequency of light flicker F _d3 ( _figure 2, time point T ₁₄ ). The value of the frequency discrimination threshold ΔF _{d is} calculated as the absolute difference between the third decrement F _d3 and the initial F _n light flicker frequencies according to the formula

ΔF _d = | F _d3 -F _n |.

The bandwidth of the spatial-frequency channel AF is determined as the arithmetic mean of the thresholds for distinguishing the frequencies of light flicker ΔF _and and ΔF _d calculated at the first and second stages of measurements by the formula

ΔF = (ΔF _and + ΔF _d ) / 2.

Thus, the inventive method for determining the bandwidth of the spatial frequency channel has the properties that determine the receipt of a positive effect.

Example. Subject L., 22 years old, using a personal computer compatible with IBM PC, was presented through the LPT port on the LEDs of the remote control of the subject light flicker with a given initial frequency F _n equal to 10 Hz (figure 1, the time interval O-T ₁ ), the frequency of light flickering of the first LED was not changed.

In the process of measurement through the LPT port, the signals from the buttons "Continuous fast change", "Continuous slow change", "Discrete change" and "Measurement" were sent to the personal computer from the test person’s remote control.

Upon receipt of a signal from the “Change Continuous Fast” button, the computer at the first stage continuously increased the frequency of light flicker of the second LED at a constant speed of 0.5 Hz / s, at the second stage it continuously decreased at the same speed.

Upon receipt of a signal from the Change Continuous Slow button, the computer in the first stage continuously decreased the frequency of light flickering of the second LED at a constant speed of 0.25 Hz / s, and in the second stage, it continuously increased with the same speed.

Upon receipt of a signal from the “Change Discrete” button, the computer at the first stage discretely increased the frequency of light flickering of the second LED with a step of 0.1 Hz, and at the second stage, it decreased with the same step.

When removing the signal from the buttons, I fixed the current incremental F _and decrement F _d frequencies presented.

On a signal from the button "Measurement" computer in the first step calculates a value distinguishing threshold requirements frequencies of light flashes as the difference between the last recorded incremental F _u and the initial F _n frequencies, and then imposes the subject at the second LED lighting flicker with a predetermined initial F _n frequency equal to 10 Hz At the second stage, the computer calculated the threshold value for distinguishing the presented frequencies of light flicker as the absolute difference between the last recorded decrement F _d and the initial F _n frequencies, then calculated the passband of the spatial-frequency channel as the arithmetic mean of the threshold values for distinguishing the frequencies of light flicker calculated on the first and second stages, displayed the value of the passband on the monitor screen, and then presented the subject to the second LED light flicker with a given initial No F _{n with a} frequency equal to 10 Hz.

At the first stage of measurements, the subject, closing the button "Change continuous fast", subjectively determined the difference between the initial F _n and incremental F _and frequencies (Fig. 1, time interval T ₁ -T ₂ ) and opened the button (Fig. 1, time point T ₂ ). In this case, the computer recorded the first incremental frequency F _{and 1} and presented light to the subject on the second LED with flickering with a fixed incremental frequency F _{and 1} (Fig. 1, time interval T ₂ -T ₃ ).

Then the subject, closing the button "Change is continuous slow", determined subjectively that the presented light flicker with the initial F _n and incremental F _and frequencies do not differ (Fig. 1, time interval T ₃ -T ₄ ) and opened the button (Fig. 1, point in time T ₄ ). At the same time, the computer recorded the second incremental frequency F _{and 2} and presented light to the test subject on the second LED with a fixed incremental frequency F _{and 2} (Fig. 1, time interval T ₄ -T ₅ )

After that, the test subject, sequentially closing the “Discrete Change” button, determined the threshold for distinguishing the presented light flickers with initial F _n and incremental F _and frequencies (Fig. 1, time interval T ₅ -T ₆ ) and closed the "Measurement" button (Fig. 1 , time T ₇ ). In this case, the computer recorded the third incremental frequency F and _{3 of} light flickers, calculated the value of the frequency discrimination threshold ΔF _, and presented the test subject with the second LED light flickers with an initial F _n frequency of 10 Hz.

At the second stage of measurements, the subject, closing the button "Change continuous fast", subjectively determined the difference between the initial F _n and decrement F _d frequencies (figure 2, the time interval T ₈ -T ₉ ) and opened the button (figure 2, time T ₉ ). In this case, the computer recorded the first decrement frequency F _d1 and presented the subject with a second light-emitting diode flicker with a fixed decrement frequency F _d1 ( _figure 2, the time interval T ₉ -T ₁₀ ).

Then the subject, closing the button "Change is continuous slow", determined subjectively that the presented light flicker with the initial F _n and decrement F _d frequencies do not differ (figure 2, the time interval T ₁₀ -T ₁₁ ) and opened the button (figure 2, point in time T ₁₁ ). In this case, the computer recorded the second decrement frequency F _d2 and presented to the test subject on the second LED light flickers with a fixed decrement frequency F _d2 ( _figure 2, the time interval T ₁₁ -T ₁₂ )

After that, the subject, sequentially closing the button "Change discrete", determined the threshold for distinguishing the presented light flicker with the initial F _n and decrement F _d frequencies (figure 2, the time interval T ₁₂ -T ₁₃ ) and closed the button "Measurement" (figure 2 , time T ₁₄ ). At the same time, the computer recorded the third decrement frequency F _{d3 of} light flickers, calculated the threshold of frequency discrimination ΔF _d2 , the bandwidth of the spatial-frequency channel ΔF, equal to 0.9 Hz, brought it to the monitor screen and presented light to the subject on the second LED with flickering F _{n with a} frequency equal to 10 Hz.

In accordance with the recommendations of physiologists, the subject performed a series of 10 measurements, as a result of which the following values of the passband of the spatial-frequency channel in Hz were obtained: 0.9; 0.7; 1.0; 1.3; 1.1; 0.8; 0.8; 1.3; 1.4; 1.1. The arithmetic mean of the measured values of the passband of the spatial frequency channel was 1.0 Hz, the standard deviation was 0.076 Hz, the confidence limits of the random component of the error of the measurement results with a confidence probability of 0.95, taking into account the student coefficient, 0.173 Hz.

As a result of measurements made by test subject L. by a known method [8], the following values of the passband of the spatial-frequency channel in Hz were obtained: 0.6; 1.0; 0.8; 1,2; 0.7; 0.5; 1,2; 1.4; 0.9; 0.7. The arithmetic mean of the measured values of the passband of the spatial frequency channel was 0.9 Hz, the standard deviation was 0.093 Hz, the confidence limits of the random component of the error of the measurement results with a confidence probability of 0.95, taking into account the student coefficient, 0.211 Hz.

The decrease in the random component of the measurement error (standard deviation) when performing measurements according to the proposed method compared with measurements performed by the known method [8], was 18.3%.

To assess the reliability of reducing the random component of the measurement error, we measured the bandwidth of the spatial-frequency channel according to the proposed and known methods for a group of 10 subjects, each of which performed a series of 10 measurements for each method. The decrease in the random component of the measurement error when performing measurements according to the proposed method compared with measurements made by the known method, ranged from 12 to 27%.

Thus, the proposed method allows to increase the accuracy of determining the bandwidth of the spatial frequency channel.

Information sources

1. Kelly D.H. Spatial frequency, bandwidth, resolution // Appl. Optics - 1965. - V.4. - No. 2. - R. 435-437.

2. Campbell F.W., Robson J. Application of Fourier analysis to the visibility of gratings // J.Physiol. - 1968. - V.197. - Number 3. - P.551-561.

3. Blakemore C. B., Campbell F.W. On the existence in the human visual system of neurons selectively sensitive to the orientation and size of retinal images // J.Physiol. - 1969. - V.203. - No. 1. - P.237-260.

4. Shelepin Yu.E., Kolesnikova L.N., Levkovich Yu.I. Visocontrastometry: Measurement of the spatial transfer functions of the visual system. - L .: Nauka, 1985 .-- 103 p.

5. Glezer V.D. Vision and thinking. Ed. 2nd, rev. and add. - St. Petersburg: Nauka, 1993.-284 p.

6. Green D.G., Campbell F.W. Effect of focus on the visual response to a sinusoidally modulated spatial stimulus // J.Opt. Soc. Amer. - 1965. - V.55. - No. 9. - P.1154-1157.

7. Bolsunov K.N. Method and means of visocontrastometry for the tasks of early diagnosis of visual impairment: Author. dis. Cand. tech. sciences. - St. Petersburg., 1997 .-- 15 p.

8. Patent 2211657 of the Russian Federation, А61В 3/00. The method of determining the bandwidth of the spatial frequency channels of the visual system. / V.V. Rozhentsov, T.A. Lezhnina (RF). - Publ. 09/10/2003, bull. Number 25. - 8 p.

Claims (1)

A method for determining the bandwidth of the spatial frequency channel of the visual system by presenting light flickers to the test subject, namely, the test subject is presented with light flickers with an initial frequency set in the visible frequency range and light flickers with an increase compared to the initial one — incremental or decreased compared to the initial - decrement frequencies, at the first stage of measurements, the incremental frequency of light flickers is initially continuously increased at a constant speed of 0.5 Hz / s until the subject subjectively determines the difference between the initial and incremental frequencies presented and fixes at this moment the first incremental frequency of light flickers; then the incremental frequency of light flicker is reduced at a constant speed of 0.25 Hz / s until the subject determines when the presented light flicker with the initial and incremental frequencies do not differ, and does not fix at this moment the second incremental frequency of light flicker, after which the incremental frequency of light flickers is increased discretely with a step of 0.1 Hz until the subject determines the threshold for distinguishing the presented light flickers from the initial and incremental frequencies and fixes the third incremental light flicker frequency; the threshold value is calculated as the difference between the third incremental and initial light flicker frequencies; at the second stage of measurements, the decrement frequency of light flickers is first continuously reduced at a constant speed of 0.5 Hz / s until the subject determines subjectively the difference between the initial and decrement frequencies presented and fixes at this moment the first decrement frequency of light flickers; then the decrement frequency of light flickers is increased with a constant speed of 0.25 Hz / s until the subject determines when the presented light flickers with initial and decrement frequencies do not differ, and does not fix the second decrement frequency of light flickers at this moment; after that, the decreasing frequency of light flickers is reduced discretely with a step of 0.1 Hz until the subject determines the threshold for distinguishing the presented light flickers with initial and decrement frequencies and fixes the third decrement frequency of light flickers; the threshold value is calculated as the absolute difference between the third decrement and initial light flicker frequencies; the passband of the spatial frequency channel is determined as the arithmetic mean of the thresholds for distinguishing the frequencies of light flicker calculated at the first and second stages of measurement, characterized in that the initial frequency is presented simultaneously using two LEDs, the frequency of flickering of the first LED is not changed, and incremental and decrement light flicker frequencies are presented on the second LED.

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