Novel paradigms for auditory P300 Spellers with spatial hearing: two online studies.
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1
Berlin Institute of Technology, Machine Learning Department, Germany
INTRODUCTION
Using Brain-computer interfaces (BCI) one can establish a communication pathway which does not rely on muscular activity. This is a promising tool for patients suffering from neurodegenerative diseases like amyotrophic lateral sclerosis (ALS). Since visual BCI paradigms might not be eligible for those patients [1], auditory speller paradigms were recently investigated [2-3]. Spatial hearing has been introduced as informative cue in a BCI paradigm [2], revealing that subjects are able to focus attention to a target direction. Two online studies investigate the usability of speller paradigms with spatial auditory cues.
METHODS
The AMUSE paradigm (standing for Auditory MUlticlass Spatial ERP), as presented in [2], was adapted for online text writing. It consists of a ring with 6 audio speakers around the subject (Figure 1) which produces stimuli in a pseudo random order. Focusing attention to any of these spatial directions results in the reliable elicitations of P300 signals in the EEG after a stimulus from that direction. This effect was used for driving a BCI, whereas the selection of characters was done with an adapted version of the hex-o-spell speller [4]. 21 naive, healthy subjects participated in an online experiment with two sessions.
As a second paradigm, an auditory speller paradigm with two-dimensional cues, varying in pitch (high/medium/low) and location (left/middle/right) was investigated. The resulting nine stimuli were presented using standard headphones. They were embedded in a predictive text system, enabling to spell a letter with a 9-class decision. The cues can be visualized with a 3x3 matrix (Figure 2) and the spelling procedure is very similar to the T9 system on mobile phones, making it easy understand and apply for any user. The paradigm is called PASS2D standing for Predictive Auditory Spatial Speller with two-dimensional cues.
12 healthy subjects participated in an online experiment with the final task to spell two sentences (16 and 36 characters).
RESULTS AND DISCUSSION
The usability of two speller paradigms with spatial auditory cues (named AMUSE and PASS2D) was investigated in separate online experiments. Class-discriminative N200 and P300 components were found in both studies, revealing that subjects are capable to attend to two-dimensional auditory cues.
With the AMUSE paradigm 16 out of 21 subjects were able to spell with a mean accuracy of ~85% and an average spelling speed of 0.592 characters/minute in the first session. In the second session, 14 out of those 16 subjects were successfully spelling with an average speed of 0.92 characters /minute.
Using the PASS2D paradigm, ten out of twelve subjects were able to spell a text with a mean selection accuracy of ~90% and an averaged spelling speed of 0.845 characters /minute.
Those results show that both paradigms are fast and accurate enough to be possibly used as a communication channel for patients that are unable to use visual spellers.
Figure 1. Experimental setup in the AMUSE paradigm.
Figure 2. Visual representation of the auditory cues in the PASS2D paradigm.
References
[1] Treder, M. S. and B. Blankertz (2010). “(C)overt attention and speller design in visual attention based brain-computer interfaces”. Behavioral Brain Functions. in press.
[2] Schreuder, M., B. Blankertz, and M. Tangermann (2010), “A new auditory multi-class brain-computer interface paradigm: spatial hearing as an informative cue”, PLoS One, vol. 5 (4)
[3] Nijboer, F., A. Furdea, I. Gunst, J. Mellinger, D. J. McFarland, N. Birbaumer, and A. Kübler (2008). “An auditory brain-computer interface (BCI)”, J Neurosci Methods 167 (1)
[4] Blankertz, B., G. Dornhege, M. Krauledat, M. Schröder, J. Williamson, R. Murray-Smith, K.-R. Müller (2006) The Berlin Brain-Computer Interface presents the novel mental typewriter Hex-o-Spell. Proceedings of the 3rd International BCI Workshop and Training Course, pp. 108-109
Keywords:
computational neuroscience
Conference:
Bernstein Conference on Computational Neuroscience, Berlin, Germany, 27 Sep - 1 Oct, 2010.
Presentation Type:
Presentation
Topic:
Bernstein Conference on Computational Neuroscience
Citation:
Höhne
J,
Schreuder
M,
Blankertz
B,
Mueller
KR and
Tangermann
M
(2010). Novel paradigms for auditory P300 Spellers with spatial hearing: two online studies..
Front. Comput. Neurosci.
Conference Abstract:
Bernstein Conference on Computational Neuroscience.
doi: 10.3389/conf.fncom.2010.51.00044
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Received:
17 Sep 2010;
Published Online:
23 Sep 2010.
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Correspondence:
Dr. Johannes Höhne, Berlin Institute of Technology, Machine Learning Department, Berlin, Germany, j.hoehne@tu-berlin.de