Sleep tracking and waking optimization system and method therefor
Analog electrical and pressure data obtained by an EEG/pressure sensor matrix from the subject are sent to a signal processing module that derives digital EEG data from the electrical signal and pressure data without using sensors attached to a subject's head. The pressure data are used as a secondary signal to measure the physical orientation of the subject's head. The physical orientation is used to transform the derived EEG signal to a known coordinate axis (the orientation of the subject's head) to obtain useful, consistent, and accurate EEG data. The EEG may be used to determine a sleep state of a subject and to awaken the subject while in a particular state.
1. A system for acquiring an EEG signal suitable for use in electroencephalography from a subject, the system comprising:
a sensor matrix comprising a plurality of EEG electrodes configured to receive electrical signals from the brain of the subject and a plurality of pressure sensors configured to receive pressure signals indicative of the placement of the head of the subject on the sensor matrix;
a processing control unit configured to perform operations comprising:
obtaining EEG electrode data from the electrical signals received by the sensor matrix;
determining a scalar EEG voltage for each EEG electrode;
obtaining pressure data from the pressure signals received by the sensor matrix;
determining a pressure normal unit vector for each EEG electrode from the pressure data;
summing the product of the pressure normal unit vector and the scalar EEG voltage for each EEG electrode to obtain a relative mean EEG vector; and
obtaining an absolute scalar EEG vector from a dot product of a unit orientation vector and the relative mean EEG vector.
2. The system of claim 1 , wherein the sensor matrix comprises a flexible sheet.
3. The system of claim 1 , wherein the sensor matrix is a component of a pillow configured for receiving the head of the subject.
4. The system of claim 1 , wherein the operation for determining a pressure normal unit vector for each EEG electrode from the pressure signals comprises:
determining from the pressure data a tilt index indicative of the orientation of the subject's head on the sensor matrix;
obtaining a tilt angle from the tilt index; and
obtaining the pressure normal unit vector from the tilt angle.
5. The system of claim 4 , wherein the operation of obtaining a tilt angle from the tilt index comprises accessing a look-up table, wherein the look-up table maps tilt index values to tilt angle values.
6. A method for acquiring an EEG signal suitable for use in electroencephalography from a subject, the method comprising:
receiving by a processor EEG electrode data from a plurality of EEG electrodes residing on a sensor matrix, wherein EEG electrode data are obtained from electrical signals from the brain of the subject;
determining by the processor a scalar EEG voltage for each EEG electrode;
receiving by the processor pressure data from a plurality of pressure sensors residing on the sensor matrix, wherein the pressure data are obtained from pressure signals indicative of the placement of the head of the subject on the sensor matrix;
determining by the processor a pressure normal unit vector for each EEG electrode from the pressure data;
summing by the processor the product of the pressure normal unit vector and the scalar EEG voltage for each EEG electrode to obtain a relative mean EEG vector; and
obtaining by the processor an absolute scalar EEG vector from a dot product of a unit orientation vector and the relative mean EEG vector.
7. The method of claim 6 , wherein the sensor matrix comprises a flexible sheet.
8. The method of claim 6 , wherein the sensor matrix is a component of a pillow configured for receiving the head of the subject.
9. The method of claim 6 , wherein determining a pressure normal unit vector for each EEG electrode from the pressure signals comprises:
determining from the pressure data a tilt index indicative of the orientation of the subject's head on the sensor matrix;
obtaining a tilt angle from the tilt index; and
obtaining the pressure normal unit vector from the tilt angle.
10. The method of claim 9 , wherein obtaining a tilt angle from the tilt index comprises accessing a look-up table, wherein the look-up table maps tilt index values to tilt angle values.
11. A system for awakening a subject, the system comprising:
a pillow comprising:
a sensor matrix, wherein the sensor matrix comprises a plurality of EEG electrodes configured to receive electrical signals from the brain of the subject and a plurality of pressure sensors configured to receive pressure signals indicative of the placement of the head of the subject on the sensor matrix;
a memory for receiving EEG electrode data derived from the electrical signals and receiving pressure data derived from the pressure signals; and
an alerting device; and
a processing control unit configured to perform operations comprising:
obtaining the EEG electrode data from the memory;
determining a scalar EEG voltage for each EEG electrode;
obtaining pressure data from the memory;
determining a pressure normal unit vector for each EEG electrode from the pressure data;
summing the product of the pressure normal unit vector and the scalar EEG voltage for each EEG electrode to obtain a relative mean EEG vector;
obtaining an absolute scalar EEG vector from a dot product of a unit orientation vector and the relative mean EEG vector;
determining a sleep state of the subject from the absolute scalar EEG vector; and
issuing a command to power on the alerting device to awaken the subject while the subject is in or is approaching a light sleep state.
12. The system of claim 11 , wherein the sensor matrix comprises a flexible sheet.
13. The system of claim 11 , wherein the operation for determining a pressure normal unit vector for each EEG electrode from the pressure signals comprises:
determining from the pressure data a tilt index indicative of the orientation of the subject's head on the sensor matrix;
obtaining a tilt angle from the tilt index; and
obtaining the pressure normal unit vector from the tilt angle.
14. The system of claim 13 , wherein the operation of obtaining a tilt angle from the tilt index comprises accessing a look-up table, wherein the look-up table maps tilt index values to tilt angle values.
15. The system of claim 11 , wherein the pillow and the processing control unit are connected to a wireless network and the operations of obtaining EEG electrode data, obtaining pressure data, and issuing a command to power on the alerting device are performed over a wireless network.
16. The system of claim 11 , wherein the processing control unit further comprises a user interface and a timer circuit and wherein the processing control unit is configured to perform operations comprising:
receiving via the user interface a wake-up time from the subject; and
issuing the command to the alerting device to awaken the subject while the subject is in or is approaching a light sleep state at or about the wake-up time.
17. The system of claim 11 , wherein the processing control unit is configured to perform operations comprising:
determining that the subject will not enter a light sleep state at or about the wake-up time;
issuing a first command to the alerting device to power on the alerting device at first level selected to modify a current sleep state to a light sleep state without awakening the subject;
determining a new sleep state;
issuing a second command to the alerting device to power on the alerting device at a second level selected to modify the new sleep state to a light sleep state without awakening the subject when the new sleep state is not a light sleep state; and
issuing the command to the alerting device to awaken the subject at or about the wake-up time when the subject is in or is approaching a light sleep state after the first or second commands.
18. The system of claim 11 , wherein the alerting device is selected from the group consisting of an alarm that vibrates, an alarm that issues an audible signal alarm and an alarm that vibrates and issues a audible signal.
19. The system of claim 11 , wherein the operations performed by the processing control unit are performed by a computing device selected from the group consisting of a laptop computer, a desktop computer, a portable computing device, a tablet and a smart phone.
20. A method for awakening a subject, the method comprising:
receiving by a processor EEG electrode data from a plurality of EEG electrodes residing on a sensor matrix, wherein EEG electrode data are obtained from electrical signals from the brain of the subject;
determining by the processor a scalar EEG voltage for each EEG electrode;
receiving by the processor pressure data from a plurality of pressure sensors residing on the sensor matrix, wherein the pressure data are obtained from pressure signals indicative of the placement of the head of the subject on the sensor matrix;
determining by the processor a pressure normal unit vector for each EEG electrode from the pressure data;
summing by the processor the product of the pressure normal unit vector and the scalar EEG voltage for each EEG electrode to obtain a relative mean EEG vector; and
obtaining by the processor an absolute scalar EEG vector from a dot product of a unit orientation vector and the relative mean EEG vector
determining a sleep state of the subject from the absolute scalar EEG vector; and
issuing a command to power on an alerting device to awaken the subject while the subject is in or is approaching a light sleep state.
21. The method of claim 20 , wherein the sensor matrix comprises a flexible sheet.
22. The method of claim 20 , wherein the sensor matrix is a component of a pillow configured for receiving the head of the subject.
23. The method of claim 20 , wherein determining a pressure normal unit vector for each EEG electrode from the pressure signals comprises:
determining from the pressure data a tilt index indicative of the orientation of the subject's head on the sensor matrix;
obtaining a tilt angle from the tilt index; and
obtaining the pressure normal unit vector from the tilt angle.
24. The method of claim 23 , wherein obtaining a tilt angle from the tilt index comprises accessing a look-up table, wherein the look-up table maps tilt index values to tilt angle values.
25. The method of claim 20 , wherein the steps of obtaining pressure data, and issuing a command to power on the alerting device are performed over a wireless network.
26. The method of claim 20 further comprising:
receiving via a user interface a wake-up time from the subject; and
issuing the command to the alerting device to awaken the subject while the subject is in or is approaching a light sleep state at or about the wake-up time.
27. The method of claim 26 further comprising:
determining that the subject will not enter a light sleep state at or about the wake-up time;
issuing a first command to the alerting device to power on the alerting device at first level selected to modify a current sleep state to a light sleep state without awakening the subject;
determining a new sleep state;
issuing a second command to the alerting device to power on the alerting device at a second level selected to modify the new sleep state to a light sleep state without awakening the subject when the new sleep state is not a light sleep state; and
issuing the command to the alerting device to awaken the subject at or about the wake-up time when the subject is in or is approaching a light sleep state after the first or second commands.
28. The method of claim 20 , wherein the alerting device is selected from the group consisting of an alarm that vibrates, an alarm that issues an audible signal alarm and an alarm that vibrates and issues an audible signal.
29. The method of claim 20 , wherein the processor is a component of a computing device selected from the group consisting of a laptop computer, a desktop computer, a portable computing device, a tablet and a smart phone.