Abstract
People with Locked-In Syndrome (LIS) have neuromuscular disabilities. Due to these lost and other situations, the concept of Brain-Computer Interface (BCI) established which translates brain wave activity to meaningful commands and helps to obtain direct connection between human brain activity and the world. It is the process of digitizing brain signals to perform specific commands on an external device. One of the BCI popular applications is the BCI speller especially the P300 speller that provides an alternative communication way for people with neuromuscular disabilities. It contains a screen of characters represented as a matrix, by which patients can select a character from it based on an Event-Related Potential (ERP) response that appears in their brain waves activity as a positive-going wave within about 300 milliseconds after selecting a desired character i.e. target, during the spelling process. In this review, we attempt to illustrate different versions of P300 spellers and describe the different paradigms of P300 speller by classifying them according to the spelling medium, the number of layers, and the flashing patterns. These paradigms including Audio P300 Speller Paradigm, Visual P300 Speller Paradigm, Visual Uni-modal P300 Speller Paradigm, Visual Bi-modal P300 Speller Paradigm, Visual Multimodal P300 Speller Paradigm, and Audiovisual P300 Speller Paradigm. We conclude this paper with some open issues in different areas, which are brain signals records, flashing patterns, paradigms, spelling duration, and BCI software. Therefore, according to the variety of P300 speller paradigms, many areas can be developed to enhance spelling performance and improve its utilization quality.