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The present day communication between humans and machines is a physical interaction and there are a few chances for the occurrence of errors. The developments in the area of communication proposed a new text entry system using eye blinks as the input modality. This was mainly designed for individuals with severe motor impairment. This implementation of the system was done using a scanning ambiguous keyboard, a keyboard that allows entering English text in less than two scanning intervals per character. The result was BlinkWrite and later few changes were done to the system that increased the text entry speed by 16% over its predecessor and 657% increase over the next fastest video-based eye blink text entry system reported in the literature.
Eyes are the most effective means of communication. Humans share considerable information through their eyes. Internet and other digital technologies enhances the human experience of communication with others. One such thing is eye typing, which would be a tremendous technology for disabled persons. Locked- in syndrome (LIS), cerebral palsy (CP) are severe disabilities that lead to complete loss of control over voluntary muscles making the individual paralyzed and mute. The above disabilities does not show any effect on the eye muscles and for individuals with such disabilities communication is very difficult and hence eyes are the main means of communication. The eyes are hence the important input modality for people with severe motor impairment and offer the means of communication with the outer world. This is all achieved by the text entry system using eye blinks.
2.1 Tracking and Typing through eyes
Eye movements are commonly captured using video cameras with infrared light to produce the reflections of the cornea. The most suitable technique for capturing interactive systems is video based capturing.
Most Video-based eye tracking interfaces, when used for input, are designed to simulate a pointing device. A common application is text entry. So called "eye typing" allows the user to enter text by looking at the keys on an on-screen keyboard [Majaranta and Raiha 2002]. These keys are selected by holding the point of gaze on a key for a predetermined time period.
The existing eye typing systems provide means of communication for the disabled individuals but, they fail to include the severely motor impaired. Considering the case of an individual with locked-in syndrome, the eye movements is limited in this case and so there can be inaccuracy in the input and so the system can be unreliable for use with eye trackers [Laureys et al. 2005]. In such case, eye blinking is the only reliable method for communication with eyes.
Most of the eye tracking systems has the capability to detect the rapid opening and closing of eyelids. The changes in the interface can make use of the blinks for the entry of text as input. In this paper, we discuss about the eye blink text entry system.
2.2. Eye Blink Text Entry
Consider the case of a person who is in the state of locked-in syndrome after suffering a massive stroke is under complete paralysis and his only means of communication was through the blink of his left eye. In his case, he took two minutes to write a typical word using blinks. The method is slow and even required two people.
The available system with text entry using blinks consists of task-based menu selections like delivering voice messages, typing, controlling home appliances, etc. Row-column scanning was used to increase the rate of item selection, as with other single-switch input methods [Baljko and Tam 2006]. Sub-tasks and the related options were displayed when the task is selected. For the typing task, a scanning keyboard with three-level selection [Bhattacharya et al.2008] and scanning intervals of two seconds was evaluated. The result was reported as 0.6 words per minute.
BlinkWriter [Krolak and Strumillo 2008] is a blinkpattern based one that replaced the popular automated scanning method for selection-traversal. Advancing to the next column and row is done by long blinks. If there is no blink detected in two seconds span then there will be advancement to the next row or column. Therefore, typing a letter needs blink and delaying makes a move to the other row or column. This has an entry time of 0.7 words per minute. Integrated text correction mechanism is not provided by these systems. BlinkWrite is the first system that met the entry speed of 4.8 words per minute and further entry speed was increased in BlinkWrite2.
BlinkWrite is a single key text entry system that uses scanning ambiguous keyboard (SAK) [MacKenzie and Ashtiani (in press)]. BlinkWrite combines scanning keyboard (one switch input) with ambiguous keyboard (one keypress per character). Here, BlinkWrite uses blinks to select keys that are scanned or highlighted on the interface.
BlinkWrite has two regions on its interface, one region for letter selection and the other for word selection. The letter selection region contains four keys. All the 26 letters of English alphabets are distributed across three keys and the fourth key is a space key. The keys are cyclically scanned and the desired letter is selected by blinking when the key is highlighted. When a key is selected, a word list is displayed in the word selection region. Scanning switches to the word region by selecting the space key when all the letters in the word are selected or the desired word is displayed earlier. This process of selection is similar to the mobile phone keypad.
Figure 1. BlinkWrite interface
The key part of the design is minimizing the average number of scan steps per character (SPC) required to enter text in English. In this design, a frequency ordered list of 9025 most common words in English are used, similar to the number in the previous text entry research [Silfverberg et al. 2000]. This design has SPC=1.713.
BlinkWrite2 is a modified and improved version of BlinkWrite, with changes in the layout and operation. In this section, the modifications to BlinkWrite are summarized.
BlinkWrite2 uses TM3 eye tracker from EyeTech Digital Systems (http://www.eyetechds.com/) to capture eye blinks. QuickGlance software acts as a hardware driver and also provides control over data capture, eye tracking, system setup and calibration. QuickLink, is an additional application programming interface that further customizes the interface and allows direct access to raw image data. In BlinkWrite, TrackerSetup is a background application developed that modified control variables of QuickGlance to enable blink clicks and disable tracking of eye movement.
QuickGlance provides various features, those sufficient for development of BlinkWrite, impose limitations for implementation of BlinkWrite2. One such limitation is that QuickGlance supports only two action intervals whereas, BlinkWrite2 needs three action intervals.
In BlinkWrite2, BlinkCapture replaces TrackerSetup of BlinkWrite. BlinkCapture is an application developed, that gains direct access to the image data of the eyes. This permitted flexibility for blink detection, interval calculations, and auditory feedback. BlinkCapture continually accesses the image data of the eyes and then reports visibility. A timer starts recording the duration when a blink is detected and stops when at least one eye is opened.
4.2 Design Improvements
The BlinkWrite system was reviewed for improvements and those flaws are implemented in designing BlinkWrite2 to make it more efficient and faster. Minimizing SPC improved the upper limit text entry speed of the system. The letter selection region of the BlinkWrite system has a space key that is used for ending letter selection and moving to the word selection region. The system had to scan the space key in every cycle that resulted in unnecessary scanning. Another flaw in the system was to scan extra letters to reach space key when letter selection was finished.
BlinkWrite2 introduced a new command, "jump" that jumps to the word selection region whenever the word needs to be chosen. The command can be accessed by implementing a new blink interval. The word selection region introduced column-row scanning of the words that reduces the number of scans to reach the desired word. The column- row scanning reduces the SPC of the system and the overall text entry speed by increasing the selections per scan step (SPS).
4.3 Blink Intervals
The blinks in BlinkWrite2 are classified based on the duration into four intervals. A new interval for "jump" command is added to the existing three intervals of the BlinkWrite. All the upper bounds and lower bounds are adjusted as required.
Blinks with an interval less than 140ms are considered involuntary and attributed as false positives in blink detection. BlinkWrite used a 200ms threshold in accordance with previous research [Grauman et al. 2003; Jacob 1990]; however this value was found to be too conservative and often voluntary blinks, causing frustration. The upper and lower bounds of the blink intervals are based on the pilot study. Blinks of duration between 140 ms and 540 ms are classified as "selection blinks". Blinks of duration between 540 ms and 1200 ms are classified as "jump blinks". Blinks with duration longer than 1200 ms are classified as "deletion blinks".
The EyeTech Digital System that is eye tracker is connected to our personal pc with windows xp and 2.0 GHz processor. Now the blink write 2 software application is displayed on the screen and then the user perform the eye blinks. The eye tracker is adjusted in such a ways it captures the eye blinks and perform the operations.
Figure 4. Experimental apparatus used for BlinkWrite2 evaluation. The EyeTech Digital Systems TM3 is identified by the block arrow.
The arrow is pointing towards the eye reader and it is adjusted in such a way that captures the eye blinks accurately.
Prior to the data collection the software is completely demonstrated so that the data access, word selection and error correction and feedback can be easily determined. The eye tracker is adjusted with the appropriate distance and the appropriate angle so the eyes will not get strained and get into a lock in syndrome.
6. Results and Discussion
As per the analysis the BlinkWrite2 technique has shown improvements in speed, Accuracy and scanning interval of the text while entering into the electronic device such as PC.
The speed of text entry has increased by 16% by using BlinkWrite2 when compared with that of BlinkWrite. Apart from BlinkWrite when we compared with the other techniques which use eye blinks as the input mode the speed of text entry by using BlinkWrite2 has drastically increased by 657%.
The accuracy while entering the text also improved. The former were computed using the minimum string distance (MSD) method of comparing the presented text string with the transcribed text string [MacKenzie and Soukoreff 2002].
The Scanning interval was optimized by analyzing the user behavior by which the text entry speed has improved and errors have decreased and the deletion of the text entered has reduced.
The improvements to the text entry system BlinkWrite and the scanning ambiguous keyboard are implemented and an improved text entry system BlinkWrite2 is obtained that achieved a text entry speed that is 16% increase over BlinkWrite and a 657% increase over the fastest eye blink text entry system that has been reported. Thus, BlinkWrite2 is a reliable text entry method for users with severe motor disabilities.