Blink detection apparatus
A blink detection apparatus includes an eyelid state index value measurement unit configured to chronologically measure an eyelid state index value, and a signal processing device. The signal processing device is configured to determine that a blink occurs when a change width of the measured eyelid state index value from a baseline that is a reference value of the eyelid state index value in a case where eyelids are in an opened state exceeds a magnitude of a threshold from the baseline, to count the number of times when the change width of the measured eyelid state index value from the baseline exceeds the magnitude of a tentative threshold from the baseline, and to set the threshold to a tentative threshold at which change in the number of times with respect to the tentative threshold is minimal.
1. A blink detection apparatus comprising:
an ocular potential measurement unit having a pair of electrodes, the ocular potential measurement unit configured to sequentially measure eyelid state index values indicating a state between an opened state and a closed state of eyelids in an eye of a subject; and
a signal processing device, wherein
the signal processing device is configured
to determine, for each measured eyelid state index value, that a blink occurs when a change of the measured eyelid state index value from a baseline that is a reference value of the eyelid state index value in a case where the eyelids of the subject are in the opened state exceeds a magnitude of a threshold,
to store the sequentially measured eyelid state index values,
to count a number of times of tentative blink occurrence with respect to each of a plurality of tentative thresholds, the number of times of tentative blink occurrence being the number of times when the change of the eyelid state index value from the baseline exceeds a magnitude of a respective tentative threshold, for each of the eyelid state index values that are sequentially measured and stored over a predetermined period, the magnitudes of the tentative thresholds being different from one another,
to generate a histogram of the numbers of times of tentative blink occurrence with respect to the tentative thresholds, and
to set the threshold to a tentative threshold among the tentative thresholds at which a change curve of the histogram is minimal, the change curve representing change in the number of times of tentative blink occurrence measured between consecutively applied tentative thresholds in the histogram.
2. The blink detection apparatus according to claim 1 , wherein:
the predetermined period is a length of a predetermined time; and
the signal processing device is configured to reset the threshold for each lapse of the predetermined period.
3. The blink detection apparatus according to claim 1 , wherein:
the signal processing device is configured to reset the threshold for each lapse of the predetermined period.
4. The blink detection apparatus according to claim 1 , wherein:
the tentative threshold at which the change curve is minimal is a tentative threshold at which a standard deviation in the number of times of tentative blink occurrence with respect to a predetermined number of adjacent tentative thresholds in the histogram is minimal, among the tentative thresholds.
5. The blink detection apparatus according to claim 1 , wherein:
the ocular potential measurement unit is configured to measure an ocular potential of the subject; and
the eyelid state index value is the ocular potential.
6. The blink detection apparatus according to claim 1 , wherein:
the ocular potential measurement unit is configured to capture an image of the eye of the subject and to detect a degree of opening of the eyelids in the image of the eye; and
the eyelid state index value is an index value indicating the degree of opening of the eyelids in the image of the eye.
7. A blink detection apparatus comprising:
an ocular potential measurement unit having a pair of electrodes, the ocular potential measurement unit configured to sequentially measure eyelid state index values indicating a state between an opened state and a closed state of eyelids in an eye of a subject; and
a signal processing device, wherein
the signal processing device is configured
to determine, for each measured eyelid state index value, that a blink occurs when a change of the measured eyelid state index value from a baseline that is a reference value of the eyelid state index value in a case where the eyelids of the subject are in the opened state exceeds a magnitude of a threshold,
to store the sequentially measured eyelid state index values,
to count a number of times of tentative blink occurrence with respect to each of a plurality of tentative thresholds, the number of times of tentative blink occurrence being the number of times when the change of the eyelid state index value from the baseline exceeds a magnitude of a respective tentative threshold, for each of the eyelid state index values that are sequentially measured and stored over a determined period, the magnitudes of the tentative thresholds being different from one another,
to generate a histogram of the numbers of times of tentative blink occurrence with respect to the tentative thresholds, and
to set the threshold to a tentative threshold among the tentative thresholds at which a change curve of the histogram is minimal, the change curve representing change in the number of times of tentative blink occurrence measured between consecutively applied tentative thresholds in the histogram,
wherein the determined period is a period until the number of times of tentative blink occurrence that is determined by the signal processing device reaches a determined number of times; and
wherein the signal processing device is configured to reset the threshold for each lapse of the determined period.