199
Measurement of Brain Activity Using Optical and Electrical Methods
output measured by the hybrid sensor probe was decreased. Upon detection of a decrease in the optical output, the movement of the assistive device
was changed into bend or extension. A single binary signal created by the
controller after analyzing the signals from the optical sensor turned the
actuator inside the device on and off. The control board was programmed
to invert the state of the actuator. The state of the actuator was controlled
every 0.8 sec. The control signal was inverted when the maximum of the signals measured by optical sensors during 0.8 s went below a threshold value.
The threshold value was chosen by observing the data collected during the
relaxation and metal calculation phase of the optical data collection experiment. A period of 0.8 s was chosen because that was the average heartbeat
period of the participant. Ideally, each time the participant focused on a
mental task the assistive device would turn on or off.
The participant and his task were the same as in the last experiment. He
was given a push switch to use to press to signify when he started the mind
task. The timing of the beginning of the mental calculations was determined
by the participant.
10.5 Result
10.5.1 Verification of Operation of the Hybrid Sensor Probe
Figure 10.6 shows the variation of the optical output. The intensity changed
periodically. Pulse waves rise up in the heart’s contraction phase and fall
in the diastole phase. The pulse wave has an inflection point in the diastole
phase. The signals measured in this experiment had the same characteristics
of the pulse waves.
Figure 10.7 shows a spectrogram of the EEG signals measured by the
electrodes. The frequency band of alpha waves is 8–13 Hz. While the
subject’s eyes were closed, the signal intensity around 10 Hz was strong.
At 18 s, the subject’s eyes opened and the signal intensity around 10 Hz
became weak. Therefore, alpha waves could be measured with the hybrid
sensor probe.
10.5.2 Optical Data Collection Experiment
As shown in Figure 10.8, the optical output was found to be high when the
participant was in relaxed state. On the other hand, while the participant
was executing mental calculations such as algebra the optical output was
lowered.
Measurement of Brain Activity Using Optical and Electrical Methods
output measured by the hybrid sensor probe was decreased. Upon detection of a decrease in the optical output, the movement of the assistive device
was changed into bend or extension. A single binary signal created by the
controller after analyzing the signals from the optical sensor turned the
actuator inside the device on and off. The control board was programmed
to invert the state of the actuator. The state of the actuator was controlled
every 0.8 sec. The control signal was inverted when the maximum of the signals measured by optical sensors during 0.8 s went below a threshold value.
The threshold value was chosen by observing the data collected during the
relaxation and metal calculation phase of the optical data collection experiment. A period of 0.8 s was chosen because that was the average heartbeat
period of the participant. Ideally, each time the participant focused on a
mental task the assistive device would turn on or off.
The participant and his task were the same as in the last experiment. He
was given a push switch to use to press to signify when he started the mind
task. The timing of the beginning of the mental calculations was determined
by the participant.
10.5 Result
10.5.1 Verification of Operation of the Hybrid Sensor Probe
Figure 10.6 shows the variation of the optical output. The intensity changed
periodically. Pulse waves rise up in the heart’s contraction phase and fall
in the diastole phase. The pulse wave has an inflection point in the diastole
phase. The signals measured in this experiment had the same characteristics
of the pulse waves.
Figure 10.7 shows a spectrogram of the EEG signals measured by the
electrodes. The frequency band of alpha waves is 8–13 Hz. While the
subject’s eyes were closed, the signal intensity around 10 Hz was strong.
At 18 s, the subject’s eyes opened and the signal intensity around 10 Hz
became weak. Therefore, alpha waves could be measured with the hybrid
sensor probe.
10.5.2 Optical Data Collection Experiment
As shown in Figure 10.8, the optical output was found to be high when the
participant was in relaxed state. On the other hand, while the participant
was executing mental calculations such as algebra the optical output was
lowered.