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UBC Theses and Dissertations

The LF-ASD brain-computer interface : preliminary on-line identification of imagined finger flexions in spontaneous EEG Bozorgzadeh, Ziba


The brain-computer interface (BCI) has emerged as a potential and radically new mode of communication for users with neuromuscular impairments since it provides a communication channel based on human brain activity as opposed to peripheral nerves and muscles. The main goal of this research study was to test the effectiveness of the Low-Frequency Asynchronous Switch Design (LF-ASD) BCI technique, which has been designed to detect imagined finger flexion patterns in an asynchronous control environment. A system was developed to study the LF-ASD with imaginary movements in subjects with spinal cord injuries. The new system was evaluated in two studies in which able-bodied and spinal cord injured subjects were asked to control the LF-ASD through movement imagination. In addition to the self-reported errors (false positives and false negatives), another class of errors, "lucky hits" (LHs), was recognized and a methodology for its estimation was introduced. In Study 1, two able-bodied subjects were asked to imagine right-hand index finger flexions. The estimated system performance (including the L H estimation results) for Study 1 produced true positive (hit) rates in the range of 57% to 68% with corresponding false positive rates in the range of 1.2% to 3.4%. The algorithm was modified to reduce false positive rates and was tested in a second study with two subjects with spinal cord injuries. In Study 2, the estimated system performance (including the LH estimation results) produced hit rates in the range of 34.7% to 41.3% with corresponding false positive rates in the range of 0.1% to 1.0%. The results of these studies provided strong evidence that able-bodied subjects as well as SCI subjects can activate the on-line LF-ASD with imagined/attempted right-hand index finger flexions. The ensemble averages of the single-trial bipolar difference of F C ₁ - C ₁ electrode signals, as well as the monopolar electrode signals C ₁ , C [sub z] and C ₂ for uncontaminated hits for both studies provided further evidence that the LF-ASD feature set can be used to detect imagined voluntary movements by subjects with spinal cord injuries. The results of this research provide positive initial indications that the LF-ASD can be activated with imagined/attempted movements. This was a fundamental step in the development of the LF-ASD BCI system given that its design was based on two unverified assumptions that 1) imagined movements will have enough similarity with actual movements to drive the LF-ASD, and 2) people with spinal cord injuries can produce consistently detectable imagined voluntary movement-related patterns similar to able-bodied people. The work of this thesis provides further evidence that a BCI system based on the LF-ASD technique may be possible to assist people with a high level of motor impairment to control devices through the preparation or imagination of motor-related tasks.

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