RU2302200C1 - Device for measuring time of excitation of human vision analyzer - Google Patents

Abstract

FIELD: medical equipment.

SUBSTANCE: device can be used for testing human vision system. Device has nanosecond pulse oscillator, microsecond pulse oscillator, first to fourth single-pulse vibrators, OR gate, reversible counter, time interval former, point light source, indication unit, five pulse series oscillator, first and second switches. Precision of measurement of excitation time of vision analyzer can be improved to ability of changing pulse duration with step of 1 microsecond.

EFFECT: improved precision of measurement.

4 dwg

Description

The invention relates to medicine and is intended to determine the time of excitation of the human visual analyzer.

Known three-channel tachistoscope for measuring the threshold time required to recognize the presented images [1]. This device in the center of the pre-exposure field projects a fixation point, which is used as a ready signal. The fronts of the exposure field are 1.5–2.0 ms. Exposure times vary using an electronic device with a minimum step of 1.5 ms.

The disadvantage of this tachistoscope is the low accuracy of measuring the threshold time for image recognition, due to the extended edges of the exposure field, comprising 1.5-2 ms, and the minimum step of changing the exposure time equal to 1.5 ms.

A device is known for measuring and recording on a machine carrier time intervals between the moment of stimulation and successive reaction impulses of a neuron. The device comprises a reference frequency generator, a 12-bit counter, a storage device, an input node, a control circuit, an address driver, an indication circuit, and a buffer register [2].

The disadvantage of this device is the inability to determine the excitation time of the visual analyzer as a whole, since in this device the time between the moment of irritation and the reaction of a neuron or group of neurons is measured. It is known that when the brain is activated, one and the same neuron can respond to stimulation with both increased and decreased impulses [3]. In this case, the cyclicality of the oscillations of the frequency of the background neuronal impulse was found and it was found that the response of the neuron depends on what phase of the cycle the stimulus fell into [4]. In addition, the existence of many different neurons with specific signal processing functions has been established [5]; therefore, based on the response of an individual neuron or group of neurons, one cannot judge the time of excitation of the visual analyzer as a whole.

The closest in technical essence to the present invention is a device for studying the inertia parameters of the human visual system, comprising a control panel, a point light source, a counter, an indication unit, a pulse generator, a millisecond pulse generator, a first one-shot, a second one-shot with an adjustable pulse duration, a third one-shot , OR element and AND element, the output of which is connected to the first input of the counter, the output of the counter is connected to the first input of the display unit, the first the control panel stroke is connected to the first input of the light source, the output of the first single vibrator is connected to the second counter input, the second input of the display unit is connected to the second output of the control panel, the millisecond pulse generator output is connected to the first input of the And element, the output of the second pulse generator is connected to the input of the first single vibrator the output of which is connected to the first input of the OR element and to the first input of the second one-shot with an adjustable pulse duration, the output of which is connected to the second input of the element and D and to the input of the third monostable multivibrator, whose output is connected to the second input of the OR gate, whose output is connected to the second input of the light source, the third remote control output connected to the second input of the second monostable multivibrator with variable pulse length [6].

It was experimentally established that the disadvantage of this device is the low accuracy of measuring the inertia parameters of the human visual system, due to the impossibility of changing the pulse duration at the output of the second one-shot in 1 ms increments. The minimum step of changing the pulse duration is limited by the resolution of the potentiometer of the control panel, that is, the smallest change in the angle of rotation of the movable system of the potentiometer, at which the change in resistance can be distinguishable [7].

The excitation time of the visual analyzer can be determined by the minimum duration of the light pulse perceived by the subject. However, it was experimentally established that when the duration of light pulses is less than 3 ms, the intensity of subjectively perceived radiation decreases. An increase in radiation intensity to a normal subjectively perceived level is undesirable due to possible damage to the retina of the visual analyzer [8].

At the same time, it is known that on- and off-systems in the visual analyzer, which respectively generate a signal about the appearance and end of a light stimulus, function independently of each other [9, 10], and their dynamics are similar [11]. This allows you to determine the excitation time of the visual analyzer, that is, the on-system, by the equal time of the excitation of the off-system.

The proposed device allows you to change the pulse duration in increments of 1 ms, thereby increasing the accuracy of determining the time of excitation of the human visual analyzer, eliminating the risk of damage to the retina by the high intensity of the applied light pulses.

In the present invention, in a device for studying the inertia parameters of the human visual system, comprising a second pulse generator, a millisecond pulse generator, a first, second and third one-vibrator, an OR element, a counter, a point light source and an indication unit, the output of the second pulse generator is connected to the input of the first one-vibrator the output of which is connected to the input of the second one-shot and the first input of the OR element, the second input of which is connected to the output of the third one-shot, and the output to the input and light source, the output of the counter is connected to the input of the display unit, a time interval former, a five-pulse series generator, a fourth one-shot, the first and second keys are additionally introduced, and the output of the first key is connected to the input of the fourth one-shot, the output of which is connected to the first input of the counter, the output the second key is connected to the input of a generator of a series of five pulses, the output of which is connected to the second input of the counter, the output of which is also connected to the first input of the shaper of the time interval, the second input to orogo generator connected to the output pulses of millisecond, the third input - with the output of the second monostable multivibrator, while the output - to the input of the third monostable multivibrator.

The inventive device allows, thanks to the introduction of a time interval shaper, a generator of a series of five pulses, a fourth one-shot, the first and second keys:

- to increase the accuracy of determining the time of excitation of the human visual analyzer due to the possibility of changing the pulse duration in increments of 1 ms;

- determine the time of excitation of the human visual analyzer, eliminating the risk of damage to the retina by the high intensity of the presented light pulses.

Thus, the claimed device differs from the known new properties that determine the receipt of a positive effect.

Figure 1 presents a structural diagram of the inventive device, figure 2 is a timing diagram of its operation, figure 3 is a timing chart of the duration of the interpulse interval between light pulses in a pair when determining the excitation time of the visual analyzer.

Figure 4 presents the timing diagrams of two light pulses of duration τ _imp , separated by the interpulse interval t of the _mission , and the visual sensations caused by them, where:

- figa is a timing diagram of two light pulses separated by an interpulse interval t _mission , causing a visual sensation of separation of pulses;

- figb - time diagram of the visual sensation of the two light pulses shown in figa;

- FIG. 4c is a timing diagram of two light pulses separated by a threshold inter-pulse interval t _then , at which a subjective sensation of fusion of two light pulses in a pair into one is achieved;

- Fig.4g is a timing diagram of the visual sensation of two light pulses shown in Fig.4B;

- τ _on is the time of on-system excitation of the visual analyzer — the summation time of the on-system is necessary for the visual sensation of the onset of the stimulus to appear, that is, the time between the moment of light exposure on the retina and the moment the corresponding visual sensation occurs [12, 13, 14] (Fig. .4b);

- τ _off is the excitation time of the off-system of the visual analyzer is the summation time of the off-system necessary for the visual sensation of the end of the stimulus to occur (Fig. 4b).

The inventive device comprises a generator of 1 second pulses, a generator of 2 millisecond pulses, a first 3, a second 4, a third 5 and a fourth 6 single vibrators, an OR element 7, a reversible counter 8, a time interval shaper 9, a point light source 10, an indication unit 11, an indicator 12 series of five pulses, the first 13 and second 14 keys.

The generator of 1 second pulses is designed to generate a sequence of pulses with a frequency of 1 Hz, providing a given repetition time of paired light pulses, and can be performed according to the known scheme.

The generator of 2 millisecond pulses is designed to generate a sequence of counting pulses with a frequency of 1 kHz, providing a measurement accuracy of 1 ms, and can be performed according to the known scheme.

The first 3 and third 5 single vibrators are designed to generate paired test pulses of 200 ms duration, the second 4 single vibrator is the start pulse of the required duration for the shaper 9 time intervals, the fourth 6 single vibrator is used to generate a short pulse to eliminate the “ringing” of the contacts of the first key 13. Single vibrators 3-6 can be performed, for example, using the K155AG1 microcircuit, which can be triggered both on the leading and trailing edges of the incoming pulses, according to the scheme in Fig.4.20, p.216 [15].

The counter 8 is made reversible. The time interval shaper 9 is intended for the formation of an inter-pulse interval between two pulses in a pair with an accuracy of 1 ms and can be performed, for example, according to the scheme in Fig. 7.48a, p. 265 [16].

The light source 10 is intended for the presentation of light pulses and is made point, for example, on an LED type ALS307EM.

The indicators in the display unit 11 are designed to display the value of the excitation time and can be performed, for example, on indicators of the type ALS333A.

The generator 12 of a series of five pulses can be performed, for example, similarly to generators 7 and 8 a.s. 1309062 USSR [17].

Key 13 is designed to start the fourth 6 one-shot, key 14 - to start the generator 12 of a series of five pulses.

The remaining functional units of the structural diagram of the device are well known.

The device operates as follows. When the power is turned on, the counter 8 is reset, the circuit of the time interval generator 9 and the circuit of the generator of a series of five pulses are set to the initial state (circuits not shown), the generator 1 generates second pulses (Fig. 2a), and the generator 2 produces millisecond pulses. The pulses from the output of the generator 1 are fed to the input of the first 3 one-shot, generating the first pulse with a duration of 200 ms along the leading edge of each pulse (Fig.2b), which through the 7 element OR is fed to the light source 10 (Fig.2e) and triggers the second 4 a single vibrator generating a pulse of duration necessary to start the shaper 9 of the time interval (pigv).

At the first stage (Fig. 3, the time interval T ₀ -T ₁ ), the test subject presses the key 14, the generator 12 generates a pack of five pulses, which are sent to the counter 8, are summed, the counting result is sent to the shaper 9 of the time interval and is displayed in block 11 indication. Millisecond pulses are received from the generator 2 to the shaper 9 of the time interval, after the shaper 9 is started by a pulse from the output of the second 4 single-vibrator (Fig.2c), a pulse of 5 ms duration is generated at the output of the shaper 9 (Fig.2d), a third 5 single-vibrator is launched along its trailing edge generating a second pulse with a duration of 200 ms (Fig.2d), which through the element 7 OR enters the light source 10 (Fig.2e). As a result, the test subject is presented with a sequence of paired light pulses of a duration equal to 200 ms, separated by an inter-pulse interval of 5 ms, repeated over a time interval of 1 s. Next, the subject presses the key 14 the required number of times until he determines the moment of subjective sensation of the separation of the two light pulses in a pair (figure 3, time T ₁ ).

In the second stage (figure 3, the time interval T ₁ -T ₂ ), the test subject presses the key 13, the one-shot 6 generates a pulse, which is received on the counter 8, is subtracted, the counting result is transmitted to the shaper 9 of the time interval and is displayed in the display unit 11. Similarly to the previous one, an impulse of a duration shorter than 1 ms is formed at the output of the former 9, a third 5 one-shot is launched at its trailing edge, generating a second impulse of 200 ms duration, which is transmitted to the light source 10 through the OR element 7. Next, the subject presses the key 13 the required number of times until he determines the moment of subjective sensation of the merger of two light pulses in a pair into one (Fig. 3, time point T ₂ ).

The excitation time of the visual analyzer is taken equal to the value of the pulse duration at the output of the shaper 9 at the time of the subjective sensation of the merger of two light pulses in a pair into one, which is displayed on the indicators of the display unit 12 in ms.

Upon presentation to the subject of two light pulses of duration τ _imp > τ _on , separated by an interpulse interval t _mission > t _then (Fig. 4a), the off-system of the visual analyzer is excited after the end of the first impulse and generates a signal indicating its end, therefore, the subject appears subjective sensation of separation of two light pulses (figb).

With a decrease in the duration of the inter-pulse interval between two light pulses, the perception of visual pulses becomes more difficult due to the influence of reverse masking, which consists in a deterioration in the perception of the first time pulse due to the presentation of the second pulse in the immediate spatio-temporal proximity with the first, as well as direct masking, in which the first pulse affects the quality of perception of the second [18]. Therefore, when the duration of the interpulse interval t of the _mission between two light pulses is reduced to a value of t _mission = t _then (Fig. 4c), the off-system of the visual analyzer does not have time to be excited after the end of the first pulse and generate a signal indicating its end, and the subject has a feeling subjective fusion of two light pulses into one (Fig.4g).

The duration of the threshold interpulse interval tnop between two light pulses, at which a subjective sensation of the merging of two light pulses into one is achieved, determines the threshold value of the excitation time of the off-system or an equal threshold value of the excitation time of the on-system of the visual analyzer.

During responses to light stimuli, the receptive field (RP) of a small neuron appears first. Then, the recorded RP expands, after which it weakens, fragmentes, and disappears. A statistical evaluation showed that the disappearance of the registered RP of the neuron occurs in the period from 100 to 200 ms after the appearance of the light stimulus [11]. After the disappearance of RP, neural structures return to their initial state and become ready to accept a new stimulus [19]; therefore, the duration of light pulses was taken to be 200 ms.

At an interstimulus interval of 500 ms, masking effects are absent or weakly expressed [20]. To eliminate the masking effect, the sequence of paired light pulses is repeated after a time interval of 1 s.

Thus, the proposed device allows to increase the accuracy of determining the excitation time of the human visual analyzer due to the possibility of changing the pulse duration in 1 ms increments, to determine the excitation time of the human visual analyzer, eliminating the risk of damage to the retina by the high intensity of the applied light pulses.

Information sources

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Claims (1)

A device for determining the excitation time of a human visual analyzer, comprising a second pulse generator, a millisecond pulse generator, a first, second and third single vibrator, an OR element, a counter, a point light source and an indication unit, the output of a second pulse generator is connected to the input of the first single vibrator, the output of which is connected with the input of the second one-shot and the first input of the OR element, the second input of which is connected to the output of the third one-shot, and the output is with the input of the light source, the output of the counter connected to the input of the display unit, characterized in that it additionally introduces a time interval shaper, a five-pulse series generator, a fourth one-shot, first and second keys, the output of the first key being connected to the input of the fourth one-shot, the output of which is connected to the first counter input, the output of the second key is connected to the input of a five-pulse series generator, the output of which is connected to the second input of the counter, the output of which is also connected to the first input of the time interval shaper, the second input of which th oscillator connected to the output pulses of millisecond, the third input - with the output of the second monostable multivibrator, while the output - to the input of the third monostable multivibrator.

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