BIOLOGICAL SIGNAL MEASUREMENT SYSTEM

A biological signal measurement system includes: a providing unit configured to provide a first visual stimulus including a first object visually changing at a predetermined frequency, and a second visual stimulus including a second object; a detection unit configured to detect a biological signal of the subject; a frequency analysis unit configured to perform a frequency analysis on the detected biological signal corresponding to the first visual stimulus, and derive a signal intensity of each frequency component; a determination unit configured to determine a time interval in which the subject has viewed the first visual stimulus, based on a signal intensity of a frequency component corresponding to the frequency; an extraction unit configured to extract the biological signal corresponding to the determined time interval, and corresponding to the second visual stimulus; and an output unit configured to output the extracted biological signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2022-046152, filed on Mar. 22, 2022. The contents of which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a biological signal measurement system.

2. Description of the Related Art

Conventionally, a visual stimulus is given to a subject and a biological reaction against the visual stimulus is measured. For example, with use of a brain function measurement apparatus, such as a magnetoencephalography, a brain reaction against a given visual stimulus is measured as a biological reaction.

Meanwhile, to capture the biological reaction against the visual stimulus, the subject needs to continue to view an image that gives the visual stimulus. In this case, with an increase in a measurement time, concentration of the subject decreases, so that a ratio of a biological reaction that is irrelevant to the reaction against the visual stimulus increases and it becomes difficult to capture the biological reaction with high accuracy. To cope with this, conventionally, a technology of embedding frequency information in images that give visual stimuli and distinguishing a type of an image that is viewed by the subject has been proposed (for example, Japanese Unexamined Patent Application Publication No. 2013-4006).

However, in the conventional technology, a biological reaction during a period in which the subject does not view a stimulus image is also acquired as a measurement result, so that accuracy of the acquired data may be reduced.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a biological signal measurement system includes a providing unit, a detection unit, a frequency analysis unit, a determination unit, an extraction unit, and an output unit. The providing unit is configured to provide a first visual stimulus and a second visual stimulus to a subject. The first visual stimulus includes a first object visually changing at a predetermined frequency. The second visual stimulus includes a second object. The detection unit is configured to detect a biological signal of the subject. The frequency analysis unit is configured to perform a frequency analysis on the biological signal detected by the detection unit and corresponding to the first visual stimulus, and derive a signal intensity of each frequency component. The determination unit is configured to determine a time interval in which the subject has viewed the first visual stimulus, based on a signal intensity of a frequency component corresponding to the frequency. The extraction unit is configured to extract the biological signal corresponding to the time interval determined by the determination unit, and corresponding to the second visual stimulus. The output unit is configured to output the biological signal extracted by the extraction unit.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of a biological signal measurement system will be described in detail below with reference to the accompanying drawings.

An embodiment has an object to measure a biological reaction of a subject against a visual stimulus with high accuracy.

FIG.1is a diagram illustrating an example of a system configuration of a biological signal measurement system1according to one embodiment. As illustrated inFIG.1, a biological signal measurement system1includes a visual stimulus providing apparatus10and a biological signal measurement apparatus20.

The image projection unit11is a projection device, such as a projector, that projects image light. The image projection unit11is mounted on a mounting table31or the like and projects image light toward the mirror12that is arranged above the subject U who lies on his/her back on a bed32. The mirror12and the screen13are arranged in front of eyes of the subject U who lies on his/her back on the bed32. The mirror12reflects the image light that is projected by the image projection unit11, and projects the image light on the screen13.

In the configuration as described above, the visual stimulus providing apparatus10projects a visual stimulus from the image projection unit11, and provides the visual stimulus in front of the eyes of the subject U.

Meanwhile, in the present embodiment, the visual stimulus providing apparatus10is configured to project a visual stimulus on the screen13, but embodiments are not limited to this example. For example, the visual stimulus providing apparatus10may display a visual stimulus on a display device, such as a liquid crystal display (LCD). Further, for example, the visual stimulus providing apparatus10may display a visual stimulus by virtual reality (VR) or the like on a head-mounted display or the like.

The biological signal measurement apparatus20includes one or more sensor units27(seeFIG.5), such as potential sensors or magnetic sensors, and acquires, as a biological signal, a potential or a magnetic field that is generated by a living body of the subject U via the sensor units27. Further, the biological signal measurement apparatus20analyzes the biological signal that is detected from the subject U, and outputs an analysis result. An output destination of the analysis result is not specifically limited, and the analysis result may be output to a display device or a printing device (not illustrated), or data of the analysis result may be output to a storage device or a different device.

The visual stimulus that is provided by the visual stimulus providing apparatus10will be described below with reference toFIG.2AtoFIG.4. Meanwhile, provision (display) of the visual stimulus by the visual stimulus providing apparatus10may be controlled by an external apparatus other than the apparatuses illustrated in the biological signal measurement system1; however, in the present embodiment, explanation will be given based on the assumption that the biological signal measurement apparatus20controls the provision (display).

FIGS.2A and2Bare diagrams illustrating an example of the visual stimulus that is provided by the visual stimulus providing apparatus10. Here,FIG.2Aillustrates a first visual stimulus G1that is provided by the visual stimulus providing apparatus10. Further,FIG.2Billustrates a second visual stimulus G2that is provided by the visual stimulus providing apparatus10.

As illustrated inFIG.2Aand2B, each of the first visual stimulus G1and the second visual stimulus G2includes a first object110. The first object110is fixedly arranged in a screen, and is formed in a certain shape, such as a circular shape, a polygonal shape, a cross shape, or a combination of a circular shape, a polygonal shape, a cross shape, and the like. Meanwhile, an inside of the first object110may be uniformly painted, or a pattern, a photograph, an illustration, a character, or the like may be drawn inside the first object110.

The first object110is arranged in, for example, approximately the center of the screen of the visual stimulus. As one example, at least a part of the first object110is arranged in a central section when the entire screen is divided into nine sections such that each of a vertical side and a horizontal size is equally divided into three sections. Meanwhile, it is preferable that the first object110is arranged in a range in which a viewing angle of the subject U with respect to the center of the screen is equal to or smaller than 10 degrees.

Further, a size of the first object110is set to 1% or more of a size of the screen or such that a visual field from the subject U is equal to or larger than 3 to 10 degrees. By providing the first object110that is arranged as described above, the subject U is able to easily view the first object110, so that it is possible to prevent the first object110from being excluded from a viewing target.

Furthermore, in all or a part of a region of the first object110, luminance that represents the region changes at a predetermined frequency (hereinafter, also referred to as a change frequency fl) of 10 Hz or more. Meanwhile, it is preferable to set the change frequency f1 to 60 Hz or more to ensure safety, such as prevention of possibility of occurrence of photosensitive epilepsy in the subject. Moreover, it is preferable to set an upper limit to about 200 Hz because a higher frequency is less likely to be detected as a brain reaction. Furthermore, to obtain an adequate brain reaction, it is preferable to change a region that occupies at least 30% or more of an area of the first object110. In the following, a visual change of a part or all of the first object110at the change frequency f1 may also be referred to as embedding of frequency information in the first object110.

Meanwhile, a method of changing the luminance of the first object110is not specifically limited, and, for example, it may be possible to change the luminance in a continuous manner or in a stepped manner or it may be possible to switch between two states such as a bright state and a dark state in a cyclic manner.

FIGS.3A and3Bare diagrams illustrating a change in the luminance of the first object110. Here, a horizontal axis represents an elapsed time and a vertical axis represents the luminance. Further, T illustrated in the figure represents a cycle (⅟f1) of the change frequency f1.

Here,FIG.3Aillustrates an example in which the luminance of the first object110is changed based on a sine wave. In this case, the luminance continuously changes between the two states such as the bright state and the dark state. In contrast,FIG.3Billustrates an example in which the luminance of the first object110is changed based on a square wave. In this case, the luminance is changed between the two states such as the bright state and the dark state for each T/2. Meanwhile, in the case illustrated inFIG.3B, the luminance need not always be changed between the two states such as the bright state and the dark state, but may be changed among three or more states.

The luminance in the first object110may be uniformly changed or may be changed with a certain spatial pattern. Further, it is preferable that a region in which the luminance changes has a pattern, such as a stripe, a dot, a ring, or a lattice, that is formed of a plurality of constituent elements because it becomes easy to recognize a difference in a stimulus frequency.

Furthermore, the visual change of the first object110may be realized using other than the luminance. For example, it may be possible to change a color, a pattern, or the like that represents all or a part of the first object110based on the change frequency f1.

FIG.4is a diagram illustrating a visual change of the first object110. InFIG.4, a horizontal direction represents an elapsed time at a certain time interval. Further, examples of various visual changes are arranged in a vertical direction.

For example,FIG.4illustrates, at (a), an example in which the luminance of the circular first object110is changed using binary values.FIG.4illustrates, at (b), an example in which the luminance of the circular first object110is changed using three or more values (including a continuous change based on a sine wave).FIG.4illustrates, at (c), an example in which a dot noise pattern is drawn in the circular first object110and the pattern is changed.FIG.4illustrates, at (d), an example in which a lattice pattern is drawn in the circular first object110and the pattern is changed by being reversed.FIG.4illustrates, at (e), an example in which a stripe pattern is drawn in the circular first object110and the pattern is changed by being reversed or moved.FIG.4, at (f), illustrates an example in which a dot noise pattern is drawn in the cross-shaped first object110and the pattern is changed.

Furthermore, the second visual stimulus G2illustrated inFIG.2Bincludes second objects120. Each of the second objects120is formed in a circular shape, a polygonal shape, a dot shape, or a combination of the circular shape, the polygonal shape, the dot shape, and the like. Moreover, an inside of each of the second objects120may be uniformly painted, or a pattern, a photograph, an illustration, a character, or the like may be drawn inside each of the second objects120.

Furthermore, each of the second objects120may be a visual stimulus for detecting a brain reaction or a visual stimulus for measuring, for example, a cognitive function, such as a spatial cognitive function, a language cognitive function, an executive function, a working memory, or an attention, phonological processing, or a character morphology processing.

A state of each of the second objects120temporally changes by a predetermined program. For example, display and non-display may be switched at a predetermined time interval in a range from 50 milliseconds to 10 seconds. Further, each of the second objects120may be provided with motion, such as enlargement, reduction, movement, or rotation, when being displayed. Meanwhile, inFIG.2B, the example is illustrated in which the plurality of second objects120that are arranged around the first object110are moved in a radial manner.

In the present embodiment, the first visual stimulus G1and the second visual stimulus G2as described above are provided as a moving image (video) in a continuous manner. For example, the biological signal measurement apparatus20first causes the visual stimulus providing apparatus10to provide the first object110that is arranged at a fixed point and that flickers at the change frequency f1, and thereafter, causes the visual stimulus providing apparatus10to provide the second objects120that are provided with motion, such as enlargement, reduction, movement, or rotation, while continuously providing the first object110. Further, the first object110and the second objects120are repeatedly provided.

Meanwhile, if the first visual stimulus G1and the second visual stimulus G2are still images, it may be possible to first provide the first visual stimulus G1, and thereafter provide the second visual stimulus G2in a switched manner. Furthermore, a pattern of providing the visual stimulus is not limited to the example as described above.

Hereinafter, operation from start of provision of the first object110(the first visual stimulus G1) to completion of provision of the second objects120(the second visual stimulus G2) may also be referred to as a single trial. In other words, the biological signal measurement apparatus20causes the visual stimulus providing apparatus10to repeatedly provide visual stimuli by adopting a series of visual stimuli such as the first visual stimulus G1and the second visual stimulus G2as a single trial. The single trial takes about 3 seconds, for example.

The biological signal measurement apparatus20will be described below.FIG.5is a diagram illustrating an example of a hardware configuration of the biological signal measurement apparatus20. As illustrated inFIG.5, the biological signal measurement apparatus20includes a central processing unit (CPU)21, a read only memory (ROM)22, a random access memory (RAM)23, a storage unit24, a display unit25, an operating unit26, the sensor units27, and an interface unit28.

The CPU21is one example of a processor and integrally controls each of the units of the biological signal measurement apparatus20. The ROM22stores therein various programs. The RAM23is a workspace for loading a program and various kinds of data. The CPU21, the ROM22, and the RAM23realize a computer configuration of the biological signal measurement apparatus20, and function as a control unit of the biological signal measurement apparatus20.

The storage unit24is a storage device, such as a hard disk drive (HDD), a flash memory, or the like. The storage unit24stores therein various programs that are executed by the CPU21, setting information, or the like. Further, the storage unit24stores therein data of a visual stimulus that is provided by the visual stimulus providing apparatus10. Furthermore, the storage unit24also functions as a storage region for storing a biological signal that is detected from the subject U.

The display unit25is a display device, such as a liquid crystal display (LCD). The display unit25displays various kinds of information and a screen under the control of the CPU21. The operating unit26includes an input device, such as a keyboard or a mouse, and outputs a signal corresponding to user operation to the CPU21. Meanwhile, the operating unit26may be a touch panel that is arranged on a surface of the display unit25.

The sensor unit27is one example of a detection unit. The sensor unit27is a sensor device, such as a potential sensor or a magnetic sensor, and detects a potential or a magnetic field that is generated by a living body of the subject U as a biological signal. Specifically, the sensor unit27repeatedly measures, as the biological signal, a change of a potential, a magnetic field, or the like that is generated by a pulse, blood pressure, a respiratory rate, or neuro-electric activity of the subject U. Meanwhile, in the present embodiment, an example will be described in which brain neural activity of the subject U is detected as the biological signal, but a detection target is not specifically limited.

The interface unit28is a wired or wireless interface for connecting the visual stimulus providing apparatus10or the like.

A functional configuration of the biological signal measurement apparatus20will be described below.FIG.6is a diagram illustrating an example of the functional configuration of the biological signal measurement apparatus20. As illustrated inFIG.6, the biological signal measurement apparatus20includes, as functional components, an acquisition unit211, an analysis processing unit212, and an output unit213.

A part or all of the functional components included in the biological signal measurement apparatus20may be software components that are implemented by cooperation of a processor (for example, the CPU21) of the biological signal measurement apparatus20and a program that is stored in the memory (for example, the ROM22or the storage unit24). Further, a part or all of the functional components included in the biological signal measurement apparatus20may be hardware components that are implemented by a dedicated circuit or the like that is mounted on the biological signal measurement apparatus20.

The acquisition unit211acquires, in cooperation with the sensor unit27, the biological signal of the subject U that is detected by the sensor unit27. Specifically, the acquisition unit211acquires, as the biological information, a data group of biological signals that are repeatedly measured for each of trials by the sensor unit27.

FIG.7is a diagram illustrating an example of the biological signals that are detected by the sensor unit27. Here,FIG.7illustrates all of biological signals detected by the sensor unit27. The biological signals include various kinds of noise. Meanwhile, a horizontal axis represents a time axis and a vertical axis represents signal intensity.

As illustrated inFIG.7, the biological signals that are detected by the sensor unit27are obtained as waveform data. The acquisition unit211acquires, as biological information, a data group of the biological signals that are repeatedly measured by the sensor unit27for each of conditions (for example, types of visual stimuli).

Further, the acquisition unit211inputs the acquired biological information to the analysis processing unit212in addition to a measurement condition that is adopted when the biological information is measured. Examples of the measurement condition include a measurement time, an attribute of the subject U, and a type of the visual stimulus. For example, the acquisition unit211acquires a measurement time at which each of the trials is performed, a type of the visual stimulus, or the like, in cooperation with the sensor unit27, a time measurement unit (not illustrated), such as a real time clock (RTC), or the like of the visual stimulus providing apparatus10. Furthermore, for example, the acquisition unit211acquires the attribute (age, gender, or the like) of the subject U that is input via the operating unit26or the like.

Meanwhile, the acquisition unit211may input the acquired biological information and the acquired measurement condition in real time to the analysis processing unit212, or may store the acquired biological information and the acquired measurement condition in the storage unit24or the like and thereafter input the biological information and the measurement condition that are obtained through a series of the trials to the analysis processing unit212.

Moreover, the acquisition unit211may calculate a statistical value (an average value, a maximum value, a minimum value, a median value, a dispersion, or the like) from the biological information that is acquired in a predetermined time rather than inputting the biological information as it is to the analysis processing unit212, and input the calculated statistical value to the analysis processing unit212.

The analysis processing unit212analyzes the biological information (biological signal) that is detected by the sensor unit27, and outputs the biological information that is obtained when the subject U views the visual stimulus. The analysis processing unit212adopts the biological information (for example, magnetic field data) on the brain activity that is input from the acquisition unit211as an analysis target. Meanwhile, the analysis target is not limited to the brain activity, but may be a pulse, blood pressure, a respiratory rate, a cerebral blood flow, eye motion, body motion, or the like of the subject U.

Specifically, the analysis processing unit212includes a frequency analysis unit2121, a determination unit2122, and an extraction unit2123.

The frequency analysis unit2121performs a frequency analysis on the biological information, and derives signal intensity for each frequency component. Specifically, the frequency analysis unit2121performs short-time Fourier transform on a biological signal (biological information) that is detected in a time interval [T1-Δt, T1+Δt] around a time T1.

Here, for example, an intermediate time or the like of each of the trials is set as the time T1, and Δt is set to a value such that the time interval [T1-Δt, T1+Δt] is equal to or smaller than a duration of a single trial. In the present embodiment, explanation will be given based on the assumption that the time interval [T1-Δt, T1+Δt] corresponds to a duration of each of the trials. Further, the time interval [T1-Δt, T1+Δt] is included in a time in which the first object110(or the first visual stimulus G1) is being provided.

Furthermore, it is preferable that the frequency analysis unit2121performs the frequency analysis using biological information corresponding to at least two trials. More specifically, the frequency analysis unit2121performs short-time Fourier transform using the biological information corresponding to the trials, and derives, as a frequency analysis result, a result of an arithmetic mean of the waveforms that are subjected to the short-time Fourier transform. With this configuration, it is possible to reduce an influence of noise, so that it is possible to improve accuracy of the biological signal.

Moreover, the frequency analysis unit2121may perform a filtering process using a frequency response filter (for example, a band-pass filter, a low-pass filter, a high-pass filter, or a notch filter) before or after the frequency analysis as described above, and perform a process of eliminating noise in a certain frequency band that is different from the frequency band of the biological signal.

Furthermore, the frequency analysis unit2121may eliminate, as noise, information, such as a heart rate, myoelectric, or blink, that is other than the brain activity and that is included in the biological signal, using a principal component analysis (PCA), an independent component analysis (ICA), or the like in order to narrow down the information on the brain activity.

FIG.8is a diagram illustrating an example of biological signals that are subjected to the frequency analysis by the frequency analysis unit2121. A horizontal axis represents a time axis and a vertical axis represents signal intensity of the biological signals (magnetic data) related to the brain activity. Further, the waveforms inFIG.8are arithmetic means of the biological signals that are subjected to the frequency analysis. Meanwhile, inFIG.8, T0 corresponds to, for example, T1-Δt.

As illustrated inFIG.8, the biological signals that are processed by the frequency analysis unit2121are signals from which various noises are eliminated, and represent the brain activity of the subject U. InFIG.8, peaks of the biological signals appear at a time T1. Here, the time T1 corresponds to a timing at which a visual stimulus (for example, the second objects120) to be measured is provided.

Referring back toFIG.6, the determination unit2122determines the time interval [T1-Δt, T1+Δt] in which the subject U views the visual stimulus, based on signal intensity of a frequency component that corresponds to the change frequency f1 or a multiple of the change frequency f1 among the frequency components of the biological information that is processed by the frequency analysis unit2121. Operation of the determination unit2122will be described below with reference toFIG.9.

FIG.9is a diagram illustrating an example of the biological information that is processed by the frequency analysis unit2121. InFIG.9, the biological information is represented by signal intensity (power spectrum) of each frequency component. A horizontal axis represents a frequency, and “Alpha”, “Beta”, and “Gamma” correspond to frequency bands of an alpha wave, a beta wave, and a gamma wave, respectively. Further, a vertical axis represents the signal intensity.

When the subject U views the visual stimulus, the subject U receives the visual stimulus of the first object110, so that a brain reaction against the change frequency f1 appears in the biological information. For example, inFIG.9, a waveform of the signal intensity corresponding to the change frequency f1 corresponds to the brain reaction, that is, the biological reaction against the visual stimulus of the first object110.

Therefore, as illustrated inFIG.9, the determination unit2122compares the signal intensity of the frequency component corresponding to the change frequency f1 and a threshold Th that is determined in advance. Then, if the signal intensity exceeds the threshold Th, the determination unit2122determines that the subject U has viewed the visual stimulus during the time interval [T1-Δt, T1+Δt] corresponding to the biological information. In other words, the determination unit2122identifies the time interval [T1-Δt, T1+Δt] during which the subject U has viewed the visual stimulus.

In contrast, if the signal intensity of the frequency component corresponding to the change frequency f1 is equal to or smaller than the threshold Th, the determination unit2122determines that the subject U has not viewed the visual stimulus during the time interval [T1-Δt, T1+Δt] corresponding to the biological information.

Meanwhile, it is possible to set the threshold Th to an arbitrary value, but it is preferable to set the threshold Th to a value by which it is possible to significantly identify whether the visual stimulus has been viewed. For example, it may be possible to determine that the visual stimulus has been viewed if an S/N ratio of the signal intensity of the frequency component corresponding to the change frequency f1 is about two times or more. Further, it is preferable that the change frequency f1 includes a plurality of frequencies because it becomes possible to improve determination accuracy, and, in this case, it may be possible to set a threshold for each frequency.

The extraction unit2123selects biological information based on the determination result of the determination unit2122. Specifically, the extraction unit2123extracts the biological information corresponding to the time interval [T1-Δt, T1+Δt] that is determined by the determination unit2122as a time interval in which the visual stimulus has been viewed among the pieces of biological information processed by the frequency analysis unit2121. Furthermore, the extraction unit2123discards the biological information corresponding to the time interval [T1-Δt, T1+Δt] that is determined by the determination unit2122as a time interval in which the visual stimulus has not been viewed, and excludes the biological information from an extraction target.

FIG.10is a diagram illustrating an example of the biological information that is extracted by the extraction unit2123. Meanwhile,FIG.10illustrates a result of extraction of the biological information corresponding to the time interval [T1-Δt, T1+Δt] in which the subject U has viewed the visual stimulus from among the pieces of biological information for which the arithmetic means are obtained inFIG.8. Meanwhile, T0 corresponds to, for example, T1-Δt.

As illustrated inFIG.10, the extraction unit2123extracts the biological information corresponding to the time interval [T1-Δt, T1+Δt] in which the subject U has viewed the visual stimulus. With this configuration, the biological signal measurement apparatus20is able to measure the brain reaction when the subject U views the visual stimulus with high accuracy.

Referring back toFIG.6, the output unit213outputs the biological information that is extracted by the analysis processing unit212(the extraction unit2123). Specifically, the output unit213outputs a result of an arithmetic mean of the biological information (biological signals) extracted by the extraction unit. With this configuration, the output unit213is able to obtain an arithmetic mean of only the biological signals that represent the brain reaction that is caused by viewing of the visual stimulus, so that it is possible to improve measurement accuracy of the brain reaction.

Meanwhile, an output method of the output unit213is not specifically limited. For example, the output unit213may be configured to store the biological information and the measurement condition by outputting the biological information and the measurement condition to the storage unit24. Further, for example, the output unit213may display the biological information and the measurement condition on the display unit25. Furthermore, for example, the output unit213may output the biological information and the measurement condition to an external apparatus via the interface unit28or the like.

An example of operation of the biological signal measurement apparatus20will be described below with reference toFIG.11.FIG.11is a flowchart illustrating an example of a process performed by the biological signal measurement apparatus20. Meanwhile, it is assumed that, as a premise of the process, the visual stimulus providing apparatus10repeatedly provides the visual stimuli (the first object110and the second objects120) at predetermined time intervals.

First, the acquisition unit211acquires the biological information corresponding to one or more trials that are detected by the sensor unit27(Step S11). Subsequently, the frequency analysis unit2121eliminates noise by performing a frequency analysis on the biological information acquired by the sensor unit27(Step S12).

Subsequently, the determination unit2122determines a viewing state of the visual stimulus based on the signal intensity of the frequency component corresponding to the frequency information that is embedded in the visual stimulus among the frequency components of the biological information processed at Step S12(Step S13). Here, if the determination unit2122determines that the visual stimulus has been viewed (Step S14; Yes), the extraction unit2123extracts the biological information on the corresponding trial (Step S15). Subsequently, the output unit213outputs the biological information extracted at Step S15and the measurement condition in an associated manner (Step S16), and the process goes to Step S18.

In contrast, if the determination unit2122determines that the visual stimulus has not been viewed (Step S14; No), the extraction unit2123discards the biological information on the corresponding trial (Step S17), and the process goes to Step S18.

At Step S18, the analysis processing unit212determines whether an instruction on termination of the process is issued (Step S18). If the instruction on the termination of the process is not issued (Step S18; No) the analysis processing unit212returns the process to Step S11.

Furthermore, for example, if the instruction on the termination of the process is issued by the operating unit26, or if provision of the visual stimulus or sensing operation of the sensor unit27is stopped, the analysis processing unit212determines that the instruction on the termination of the process is issued (Step S18; Yes), and the process is terminated.

As described above, the biological signal measurement system1according to the present embodiment includes the visual stimulus providing apparatus10that provides the visual stimulus including the first object110that visually changes at the change frequency f1 to the subject U, and the biological signal measurement apparatus20that detects biological signals of the subject U. Furthermore, the biological signal measurement apparatus20performs a frequency analysis on the detected biological signals, derives signal intensity of each frequency component, determines a time interval in which the subject U has viewed the visual stimulus based on the signal intensity of the frequency component corresponding to the change frequency f1, and extracts and outputs a biological signal corresponding to the time interval. With this configuration, the biological signal measurement system1is able to obtain the brain reaction corresponding to a period in which the subject U has viewed the visual stimulus, so that it is possible to measure the brain reaction of the subject U against the visual stimulus with high accuracy.

Meanwhile, the embodiment as described above may be embodied with an appropriate modification by changing a part of the configuration or the function of each of the apparatuses as described above. Therefore, some modifications of the embodiment as described above will be described as different embodiments. Meanwhile, in the following, a difference from the embodiment as described above will be mainly described, and detailed explanation of the same points as the details that are already explained will be omitted. Furthermore, the modifications described below may be implemented individually or by an appropriate combination.

First Modification

In the embodiment as described above, the example has been described in which the first object110is arranged in an approximately center of the screen of the visual stimulus, but the arrangement position of the first object110is not limited to this example. For example, as illustrated inFIG.12, it may be possible to arrange the plurality of first objects110in the scree of the visual stimulus.

FIG.12is a diagram for explaining an example of a screen of a visual stimulus according to a first modification. As illustrated inFIG.12, in a visual stimulus G3, at least the single first object110is arranged in each quadrant (region) of a screen that is divided into four quadrants.

By providing the visual stimulus G3, the biological signal measurement apparatus20is able to effectively obtain the brain reaction because the first object110is viewed even if the subject U views any part of the screen. With this configuration, in the biological signal measurement system1according to the present modification, it is possible to reduce the number of pieces of biological information to be excluded, that is, the number of trials, so that it is possible to reduce the entire measurement time and reduce a load on the subject U.

Second Modification

In the embodiment as described above, the example has been described in which the first object110and the second objects120are provided as different stimulus images or stimulus videos. However, the method of providing the first object110and the second objects120is not limited to this example. Therefore, in the present modification, as one example of the providing method, a visual stimulus that is used when the first object110and the second objects120are simultaneously provided will be described.

FIG.13is a diagram for explaining an example of a screen of a visual stimulus according to a second modification. As illustrated inFIG.13, a visual stimulus G4includes the first object110that is arranged in approximately the center of the screen and the second objects120that are arranged around the first object110.

Here, the first object110is a fixed point and flickers at the change frequency f1. The second objects120are represented as a stripe pattern and colored such that white and black alternately appear. Further, the second objects120provide a reversal stimulus such that coloring of white and black changes by reversing (or moving) the coloring of white and black.

By providing the visual stimulus G4, the biological signal measurement apparatus20is able to simultaneously determine whether the subject U has viewed the first object110and acquire the brain reaction generated by the viewing of the second objects120. Therefore, the biological signal measurement system1according to the present modification is able to reduce the trial time, so that it is possible to reduce a load on the subject U.

Meanwhile, the pattern of the second objects120is not limited to a stripe pattern, but may be a lattice pattern, a checkered pattern, a concentric circle pattern, or the like.

Third Modification

In the embodiment as described above, it is explained that the frequency information is embedded in the first object110. However, the frequency information need not always be embedded in the first object110.

For example, it may be possible to embed the frequency information in the second objects120. In this case, it is preferable that a frequency band of the frequency information that is embedded in the first object110, that is, the change frequency f1 that is used to determine whether the stimulus is viewed, and a frequency band of the frequency information that is embedded in the second objects120do not overlap with each other.

With this configuration, it is possible to realize determination on whether the first object110is viewed and acquisition of the brain reaction by the second objects120by providing a single visual stimulus.

Furthermore, it may be possible to embed the frequency information in a region other than the first object110and the second objects120.FIG.14is a diagram for explaining an example of a screen of a visual stimulus according to a third modification, and illustrates an example in which the frequency information is embedded in an entire periphery other than the first object110and the second objects120.

Specifically, a visual stimulus G5illustrated inFIG.14includes the first object110that is a fixed point and two second objects120aand120bthat are rectangular shapes. Here, the frequency information on the change frequency f1 (Hz) is embedded in the first object110, and the first object110flickers at, for example, the change frequency f1.Further, frequency information on a frequency f2 (Hz) is embedded in the second object120a, and the second object120aflickers at, for example, the frequency f2. Furthermore, frequency information on a frequency f3 (Hz) is embedded in the second object120b, and the second object120bflickers at, for example, a frequency f3. Here, each of the frequencies f1, f2, and f3 belongs to a different frequency band. Meanwhile, in this case, it is preferable that the frequencies f2 and f3 are frequencies of interest that are targets for analysis of the brain reaction.

Furthermore, frequency information on a frequency f4 (Hz) is embedded in a region130that is a background of the first object110and the second objects120aand120b, and the region130flickers at, for example, the frequency f4. Meanwhile, a frequency band of the frequency f4 is different from the frequency band of any of the frequencies f1, f2, and f3.

By providing the visual stimulus G5, the biological signal measurement apparatus20is able to distinguish one of the second objects120aand120bviewed by the subject U. Further, the biological signal measurement apparatus20is able to exclude a trial that is performed when the subject U does not view any of the second objects120aand120b, such as when the subject U is sleeping. With this configuration, the biological signal measurement system1according to the present modification is able to effectively acquire the brain reaction when the second objects120aand120bare viewed, so that it is possible to improve measurement accuracy.

Meanwhile, the second objects120(120aand120b) have rectangular shapes inFIG.14, but are not limited to this example, and may have different shapes, such as circular shapes. Furthermore, the two second objects120are provided inFIG.14, but the number of the second objects120is not limited to this example. Moreover, the second object120aand the second object120bbelong to different frequency bands inFIG.14, but may belong to the same or overlapping frequency bands.

Meanwhile, the program that is executed by each of the devices in the embodiment and the modifications as described above is provided by being incorporated in a ROM, a storage unit, or the like in advance. The program executed by each of the devices of the embodiment and the modifications as described above may be provided by being recorded in a computer readable recording medium, such as a compact disk (CD)-ROM, a flexible disk (FD), or a digital versatile disk (DVD), in a computer-installable or computer-executable file format.

Furthermore, the program executed by each of the devices of the embodiment and the modifications as described above may be stored in a computer that is connected to a network, such as the Internet, and may be provided by download via the network. Moreover, the program executed by each of the devices of the embodiment and modifications as described above may be provided or distributed via a network, such as the Internet.

According to an embodiment, it is possible to measure a biological reaction of a subject against a visual stimulus with high accuracy.