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Randomized Controlled Trial
. 2014 Dec;11(6):066010.
doi: 10.1088/1741-2560/11/6/066010. Epub 2014 Nov 7.

Novel hold-release functionality in a P300 brain-computer interface

R E Alcaide-Aguirre  1 , J E Huggins
Affiliations
Randomized Controlled Trial

Novel hold-release functionality in a P300 brain-computer interface

R E Alcaide-Aguirre et al. J Neural Eng. 2014 Dec.

Abstract

Assistive technology control interface theory describes interface activation and interface deactivation as distinct properties of any control interface. Separating control of activation and deactivation allows precise timing of the duration of the activation. Objective. We propose a novel P300 brain-computer interface (BCI) functionality with separate control of the initial activation and the deactivation (hold-release) of a selection. Approach. Using two different layouts and off-line analysis, we tested the accuracy with which subjects could (1) hold their selection and (2) quickly change between selections. Main results. Mean accuracy across all subjects for the hold-release algorithm was 85% with one hold-release classification and 100% with two hold-release classifications. Using a layout designed to lower perceptual errors, accuracy increased to a mean of 90% and the time subjects could hold a selection was 40% longer than with the standard layout. Hold-release functionality provides improved response time (6-16 times faster) over the initial P300 BCI selection by allowing the BCI to make hold-release decisions from very few flashes instead of after multiple sequences of flashes. Significance. For the BCI user, hold-release functionality allows for faster, more continuous control with a P300 BCI, creating new options for BCI applications.

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Figures

Figure 1
Figure 1
Left: Example BCI matrix with targets for different actions. Some actions are enabled for hold-release functionality and others are not. Right: After the subject selects an action that is hold-release enabled, in this case recline wheelchair, the screen changes to a hold-release mode.
Figure 2
Figure 2
Layout 1 (left) represents a typical event-related potential BCI typing matrix with numbers providing visual clutter. Layout 2 (right) has asterisks instead of numbers and whitespace to reduce perceptual errors. Illuminated areas represent a flash group.
Figure 3
Figure 3
Electrode Cap montage. Circles denote electrode locations used for the study.
Figure 4
Figure 4
Sample outcomes of our hold-release protocol using layout 1 (left) and layout 2 (right) for single- (top) and double- (bottom) flash classifications. The red line shows the ideal hold result for each flash. The blue line shows which target the algorithm classified as held.
Figure 5
Figure 5
Length of consecutive correct performance intervals (in flashes) for all subjects by layout and single vs. double flash classification. Note that each run was 330 flashes.
Figure 6
Figure 6
Speed of hold-release functionality compared to a typical P300 speller.
See this image and copyright information in PMC

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