在线BCI衡量指标丨信息传输速率 Information Transfer Rate

用来衡量在线脑机接口系统的一个重要指标：信息传输速率ITR。

摘自论文：Brain-computer interface technology: a review of the first international meeting
附译论文：Design and Implementation of a Brain-Computer Interface With High Transfer Rates

论文

  Because BCI’s differ greatly in their inputs, translation algorithms, outputs, and other characteristics, they are often difficult to compare. While it is likely that different systems will prove most valuable for different applications,a standard performance measure would be useful as a general purpose benchmark for following BCI development.A standard measure of communication systems is bit rate, the amount of information communicated per unit time. Bit rate depends on both speed and accuracy [20],[21]. Fig.1 illustrates the relationship between accuracy and information transfer rate for different numbers of choices(i.e.,2,4,8,16,32). Information transfer rate is shown both as bits/trial(i.e., bits/selection), and as bits/min when 12 selections are made each min [a selection rate similar to that of several current BCI’s(e.g.,[3],[7],[8])]. Thus, for ex-ample, the information transfer rate of a BCI that can select between two possible choices with 90% accuracy is twice that of a BCI that can select between them with 80% accuracy, and equal to that of a BCI that can select between four possible choices with 65% accuracy. The enormous importance of accuracy, illustrated by the doubling in information transfer rate with improvement from 80% to 90% accuracy in a two-choice system, has not usually received appropriate recognition in BCI-related publications. While the effectiveness of each BCI system will depend in considerable part on the application to which it is applied, bit rate furnishes an objective measure for comparing different systems and for measuring improvements within systems.

  译：由于BCI在输入，转换算法，输出和其他特性方面存在很大差异，因此它们通常难以比较。虽然不同的系统很可能证明对不同的应用程序最有价值，但标准的性能指标可用作跟踪BCI开发的通用基准。通信系统的标准度量是比特率，即每单位时间传递的信息量。比特率取决于速度和准确度[20]，[21]。图1说明了不同数量的选择（即2,4,8,16,32）的准确度和信息传递率之间的关系。信息传输速率既显示为比特/试验（即比特/选择），也显示为每分钟进行12次选择时的比特/分钟[选择速率类似于几个当前BCI的选择速率（例如，[3]，[7] ]，[8]）]。因此，例如，可以在两个可能的选择之间进行选择且具有90％准确度的BCI的信息传输速率是可以在它们之间进行选择的BCI的两倍，具有80％的准确度，并且等于可以具有80％精度的BCI的信息传输速率。选择四种可能的选择，准确率为65％。信息传输速率加倍，双选系统的准确度从80％提高到90％，说明准确性的重要性，在BCI相关出版物中通常没有得到适当的认可。虽然每个BCI系统的有效性在很大程度上取决于应用它的应用，但比特率为比较不同系统和测量系统内的改进提供了客观的衡量标准。

MATLAB 实现

像开源致敬！
源码出自：TRCA-SSVEP

function [ itr ] = itr(n, p, t)
% Calculate information transfer rate (ITR) for brain-computer interface 
% (BCI) [2]
% function [ itr ] = itr(n, p, t)
% 
% Input:
%   n   : # of targets
%   p   : Target identification accuracy (0 <= p <= 1) 
%   t   : Averaged time for a selection [s]
%
% Output:
%   itr : Information transfer rate [bits/min] 
%
% Reference:
%   [1] M. Cheng, X. Gao, S. Gao, and D. Xu,
%       "Design and Implementation of a Brain-Computer Interface With High 
%        Transfer Rates",
%       IEEE Trans. Biomed. Eng. 49, 1181-1186, 2002.
% 
% Masaki Nakanishi, 22-Dec-2017
% Swartz Center for Computational Neuroscience, Institute for Neural
% Computation, University of California San Diego
% E-mail: masaki@sccn.ucsd.edu

if nargin < 3
    error('stats:itr:LackOfInput', 'Not enough input arguments.'); end

if p < 0 || 1 < p
    error('stats:itr:BadInputValue',...
        'Accuracy need to be between 0 and 1.');
elseif p < 1/n
    warning('stats:itr:BadInputValue',...
        'The ITR might be incorrect because the accuracy < chance level.');
    itr = 0;
elseif p == 1
    itr = log2(n)*60/t;
else
    itr = (log2(n) + p*log2(p) + (1-p)*log2((1-p)/(n-1)))*60/t;
end

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