Working memory is an important part of cognitive function that is the basis for learning and memory, having a close relationship with other cognitive behaviors. The cognitive functions of the brain like language, perception, planning, reasoning, and problem solving require working memory.
In recent years, many studies have been done on brain signals to be used to interpret people's mental states or intentions. Electrical brain signals or electroencephalogram (EEG) signals are the first choice in many studies on brain-computer interface. One of the most commonly used BCI systems is spellers which enable a person to spell letters using their brain signal without the need for muscle movement. These systems are appropriate for patients with neurological disorders. Accuracy and speed of spelling are two important criteria in evaluating these types of systems.