Analysis of bit-rate definitions for Brain-Computer Interfaces

A comparison of different bit-rate definitions used in the Brain-Computer Interface (BCI) community is proposed; assumptions underlying those definitions and their limitations are discussed. Capacity estimates using Wolpaw and Nykopp bit-rates are computed for various published BCIs. It appears that only Nykopp's bit-rate is coherent with channel coding theory. Wol- paw's definition might lead to underestimate the real bit- rate and to infer wrong conclusions about the optimal number of symbols; its use should be avoided. The us- age of a proper bit-rate assessment is motivated and advocated. Finally, it is found that the typical signal-to- noise ratio of current BCIs lies around 0 dB.

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