Eye Snake - Results

Speed of Execution and Accuracy

The video game code runs effectively with no flickering or unwanted artifacts. Even in button mode with push buttons, there is no noticeable delay as the player is playing the game. Each frame is 1/60 of a second, and the snake travels relatively slowly for the eyes to keep up so there is ample time for multiple lines to be drawn quickly. The only issue with the video is that the snake's movement is not smooth. This is deliberate, as we wanted to give the player additional time to change the direction of the snake, and interpolating the position between the grid cells would constrain the player to always be selecting the next direction. The speed of execution coming from the electrode signal of the eyes is usually accurate and fast enough when calibrated correctly. Before the game begins, a test subjectís electrode signal is calibrated by asking the subject to look at the center of the video screen. The accuracy is highly dependent on the calibration and that the designated center electrode signal is not drifting upward or downward. If it should drift upward and downward, it interferes the ADC calculation and prevents the signal from successfully converted into the proper direction. The only other hindrance to the accuracy of the up and down electrode pair signal is an unavoidable act of blinking, which can be registered as an up signal through the ADC. Nevertheless, our test subjects have been successfully able to play level 8 despite blinking and even utilized blinking to their advantage during game mode. Besides, the challenge of timing your blinking adds to the fun of our Snake game.

Safety and Interference

Our project has been relatively safe thus far. We successfully isolated both horizontal and vertical electrode pairs from the 110 V line. The voltage rails and pins are frequently checked before hooking the test subject up to the inputs of the instrumentation amplifier. Moreover, we tried reducing the amount of loose and exposed wiring to prevent short circuitry from occurring. The standard black and white television does not utilize flash effects so those playing Snake are not at risk of getting seizures from looking at the screen. Our circuit runs on a 9V battery with 10-20 mA of current, so itís unlikely that this circuit would cause injury. Nevertheless, for those who suffer from dry eyes or severe eye spasms that would interfere with the rotation of the eye or inability to sit still, this game of Snake may be harmful after long term use.

The EOG circuit does not generate any RF interference and has not interfered with anyone elseís project. However, wireless communication and presence of too many electronic devices can cause a noise disturbance on our circuitry. At times, a 60 Hz noise is generated on top of the electrode signal despite our low pass filter. Therefore it is recommended that this circuit be used around a limited number of CPUs and other noisy devices. It should be noted that we were able to successfully use our electrodes in a lab of more than 15 computers. In our experience, insufficiently taped electrodes generate substantially more noise and hindrance to this design than CPU or RF interference.


For the most part, our project is usable by anyone who is willing to be patient enough to be calibrated. Depending on the playerís ability to keep their head and eyes steady during the calibration, it can take anywhere between a few minutes to hours to get the person ready to play Snake. However, once calibrated and comfortably seated, many of our test subjects have indicated that this game is quite enjoyable and entertaining to play.

Our menu is relatively intuitive to use. During button mode, the user can use the pushbuttons to scroll and select accordingly. The arrow on the left side indicates which option the user is currently on. During eye mode, the user can utilize left and right signals to scroll the menu, but still needs to select using a pushbutton. Ideally up and down electrode signals would be nice to use for scrolling the menu. Unfortunately blinking is an artifact that cannot be avoided unless a player wants to risk drying their eyes out. Left and right electrode signals have thus been shown to be more effective in scrolling than up and down electrode signals.

Theo Chao (tc99), Diane Chang (dcc34) © 2005