Alertness/Drowsiness and Cognitive Capacity Index

• US 20090149770A1
• Filed: 12/19/2008
• Published: 06/11/2009
• Est. Priority Date: 06/22/2006
• Status: Active Grant

• Current Assignee: USA As Represented By The Secretary of The Army On Behalf of Usamrmc
• Original Assignee: USA As Represented By The Secretary of The Army On Behalf of Usamrmc
• Inventors: Sing, Helen C.
• Granted Patent: US 8,285,372 B2
• Time in Patent Office: Days
• US Class Current: 600/544
• CPC Class Codes: A61B 5/165 Evaluating the state of mind, e.g. depression, anxiety
• CPC Class Codes: A61B 5/18 for vehicle drivers or machine operators
• CPC Class Codes: A61B 5/316 Modalities, i.e. specific diagnostic methods
• CPC Class Codes: A61B 5/374 Detecting the frequency distribution of signals, e.g. detecting delta, theta, alpha, beta or gamma waves
• CPC Class Codes: A61B 5/7257 using Fourier transforms

Abstract

The invention includes a method and system for providing an Index representing the alertness state of an individual based at least in part on EEG signals obtained from the individual. In at least one embodiment, the EEG signals are divided into frequency bands and a total amplitude of the power is determined. Based on the proportion of the high frequency band compared to the proportion of the low frequency band, an Index is determined that is indicative of an individual'"'"'s ability to perform a cognitive task.

Claims

1. A method comprising:

transforming a EEG signal to the frequency domain with a Discrete Fourier Transform,

obtaining the amplitude of each frequency component,

summing all of the amplitudes of each frequency component to obtain a total amplitude,

summing all of the amplitudes of frequencies in the range of 201-500 Hz to obtain a high frequency amplitude,

summing all of the amplitudes of frequencies in the range of 1 to at least 15 Hz to obtain a low frequency amplitude, and

calculating an Index based on the total amplitude, the high frequency amplitude, and the low frequency amplitude.

2. The method according to claim 1, further comprising smoothing the Index.

3. The method according to claim 2, wherein smoothing the Index using a 10 point moving average.

4. The method according to claim 2, further comprising obtaining a slope value of the Index.

5. The method according to claim 1, wherein the low frequency amplitude is obtained for frequencies in the range of 1-20 Hz.

6. The method according to claim 1, further comprising:

obtaining an EEG signal, and

converting the EEG signal from analog to digital.

7. The method according to claims 6, further comprising smoothing the Index using a 10 point moving average.

8. The method according to claim 7, further comprising obtaining a slope value of the Index.

9. The method according to claim 1, wherein obtaining the amplitude of each frequency component includes grouping the frequencies into frequency bands.

10. The method according to claim 9, wherein the frequency bands include 1-15 Hz, 16-50 Hz, 51-100 Hz, 101-200 Hz, 201-300 Hz, 301-400 Hz, and 401-500 Hz.

11. The method according to claim 9, wherein the frequency bands include 1-20 Hz, 21-50 Hz, 51-100 Hz, 101-200 Hz, 201-300 Hz, 301-400 Hz, and 401-500 Hz.

12. The method according to claim 9, wherein the frequency bands include 1-15 Hz, 16-50 Hz, 51-100 Hz, 101-200 Hz, and 201-500 Hz.

13. The method according to claim 1, further comprising providing a notification when the Index is less than a threshold.

14. The method according to claim 13, wherein the threshold is equal to 1.

15. The method according to claim 13, wherein the threshold is equal to 0.8.

16. A method for determining an index representative of the level of alertness/drowsiness of an individual comprising:

receiving an EEG signal,

transforming the EEG signal into the frequency domain,

summing all of the amplitudes for each frequency band,

determining a total amplitude for all frequency bands,

determining the ratio of each frequency band to the total amplitude for at least the lowest and highest frequency band,

determining the index of the highest frequency band ratio to the lowest frequency band ratio, and

providing the index.

17. The method according to claim 16, further comprising eliminating any sample whose total amplitude exceeds a mean total amplitude plus 2 standard deviations,

where mean total amplitude is calculated from an initial sampling period for the EEG.

18. The method according to claim 16, further comprising filtering out the power line frequency and its harmonics.

19. The method according to claim 16, wherein the highest frequency band is 201-500 Hz.

20. The method according to claim 16, wherein the lowest frequency band is 1-15 Hz.

21. The method according to claim 16, wherein the lowest frequency band is 1-20 Hz.

22. A system comprising:

means for transforming an EEG signal to the frequency domain with a Discrete Fourier Transform,

means for obtaining the amplitude of each frequency component,

means for summing all of the amplitudes of each frequency component to obtain a total amplitude,

means for summing all of the amplitudes of frequencies in the range of 201-500 Hz to obtain a high frequency amplitude,

means for summing all of the amplitudes of frequencies in the range of 1 to at least 15 Hz to obtain a low frequency amplitude, and

means for calculating an Index based on the total amplitude, the high frequency amplitude, and the low frequency amplitude.

23. A system for providing an index for an individual using at least one EEG signal, said system comprising:

a Discrete Fourier transformer;

a low frequency path connected to an output of said Discrete Fourier transformer, said low frequency path includes

a low bandpass filter covering the low frequency band, and

a low frequency summation device connected to said low bandpass filter;

a high frequency path connected to an output of said Discrete Fourier transformer, said high frequency path includes

a high bandpass filter covering the high frequency band, and

a high frequency summation device connected to said high bandpass filter; and

a divider connect to said low frequency summation device and said high frequency summation device, said divider outputs a ratio of the output of said high frequency summation device to the output of said low frequency summation device.