Hi everyone! Our project is to develop a human-computer interface using eye movements. This is especially important for paralyzed people who are limited to only eye movements. Using our system, a paralyzed person could even play games on the computer!
More than 200, 000 people around the world are living with Amyotrophic Lateral Sclerosis (ALS) [1]. Other than that, people with Locked-In-Syndrome (LIS) also experience an inability to move muscles except for eye movements. Our device could be an interface that connects these differently abled people to the world through a computer.
Our device uses Electrooculography (EOG) signals generated by the eye to identify the left, right, up, and down eye movements and can be extended to identify the blink commands. An EOG signal is a bioelectric signal that measures the electrical potential between the cornea and retina of the eye. The signal changes based on eye movements. The potential increases when the cornea approaches an electrode and decreases when the cornea moves away.
From these signal patterns we are able to identify the occurred eye movement.
MethodologyThe EOG signals are captured using flexible semi-dry electrodes. They are in the microvolt range and, therefore, need to be amplified. It also needs some analog and digital filters in order to remove the noise components.
- Analog filters
- 0.1 Hz cutoff High pass filter (remove baseline wandering)
- Digital filters
- 80 Hz cutoff Low pass filter (remove high-frequency noise)
- 50 Hz, 100 Hz Notch filters (remove powerline noise)
- Median filters (for smoothing)
The ADS1299 IC is used for signal amplification and digitization. The digitized data is processed by an ESP32-S3 microcontroller and transmitted to the PC over Wi-Fi. The digital filtering is done on the PC using the Python SciPy library. The decisions (up, down, left, right) are made through a simple thresholding algorithm. After identifying the eye movement, the game is controlled by giving the command as a keyboard input. Graphing is done using Pyqtgraph.
[1] https://als.ca/what-is-als/about-als/
[2] https://www.sciencedirect.com/science/article/pii/S0167865509003596
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