Proceeding of the 11th World Congress on Intelligent Control and Automation Shenyang, China, June 29 - July 4 2014
Decreasing the interference of visual-based P300 BCI using facial expression changes* Jing Jin, Yu Zhang and Xingyu Wang Key Laboratory of Advanced Control and Optimization for Chemical Processes, Ministry of Education East China University of Science and Technology Shanghai, 200237, China
[email protected]
Ian Daly
Andrzej Cichocki, IEEE Fellow
Brain embodiment lab School of Systems Engineering
Laboratory for Advanced Brain Signal Processing, Brain Science Institute
University of Reading
RIEKN
RG6 6AY, UK
[email protected]
Wako-shi, Saitama 351-0198, Japan
[email protected]
applicability for ALS patients [6, 7], and optimizing the stimuli configuration to increase the speed and reliability[8, 9]. Enhancing the difference between attended and ignored events is one of the hot topics in the research of P300 BCI. Some groups adopted new stimulus presentation paradigms to increase other components of the ERP that occur before or after the P300. The BCI team leaded by Prof. Gao introduced a novel way to elicit visual evoked potentials in a BCI: the stimuli briefly moved, instead of flashed, to evoke a motion evoked potential (M-VEP) and reported that this BCI system might offer superior performance to a conventional P300 BCI [10, 11, 12]. Jin et al, 2012 combined the P300 and M-VEP by moving flash stimuli to improve the P300 BCI system [13]. Kaufmann et al. (2011) introduced stimuli that were transparently overlaid with famous faces to improve the classification accuracy by evoking a large N400 [14]. Zhang et al. (2012) reported that N170 and vertex positive potentials (VPP) also improve classification accuracy in a P300 BCI with stimuli that change to faces [15]. However, while this research succeeded in increasing the identifiability of target sub-trials it could not decrease the noises in non-target sub-trials caused by spatially adjacent interference leading to false positives [8, 9]. Although, some studies have tried to reduce the interference by decreasing the number of adjacent flashes [8, 9, 16], the number of flashes in each trial was increased which would reduce the speed of the BCI system. A key question is whether there is any stimuli presentation pattern that can both reduce the interference while not increasing the flash times in each trial? The new stimuli presentation pattern presented in this paper could meet this requirement. The primary goal of this study was to verify the performance of the new stimuli presentation pattern in reducing the interference. The key idea behind this work is that minor changes to the image cause a big difference. Human facial expression changes could be simulated by changing a curve in a dummy face or changing few parts of the human facial image. In this way, the subjects would not be
Abstract - Interferences from the spatially adjacent nontarget stimuli evoke ERPs during non-target sub-trials and lead to false positives. This phenomenon is commonly seen in visual attention based BCIs and affects the performance of BCI system. Although, users or subjects tried to focus on the target stimulus, they still could not help being affected by conspicuous changes of the stimuli (flashes or presenting images) which were adjacent to the target stimulus. In view of this case, the aim of this study is to reduce the adjacent interference using new stimulus presentation pattern based on facial expression changes. Positive facial expressions can be changed to negative facial expressions by minor changes to the original facial image. Although the changes are minor, the contrast will be big enough to evoke strong ERPs. In this paper, two different conditions (Pattern_1, Pattern_2) were used to compare across objective measures such as classification accuracy and information transfer rate as well as subjective measures. Pattern_1 was a “flash-only” pattern and Pattern_2 was a facial expression change of a dummy face. In the facial expression change patterns, the background is a positive facial expression and the stimulus is a negative facial expression. The results showed that the interferences from adjacent stimuli could be reduced significantly (P
