EEG activity under different speeds and prompt types in motor imagery and motor execution

Motor imagery has been widely employed in noninvasive brain-computer interface (BCI) systems. Maintaining and manipulating specific motor imagery is essential to these systems, but motor imagery is usually performed using individual strategies and thus can be quite challenging for some healthy and disabled users. Kinematic movement parameters, such as the clenching speed, are important factors affecting the modulation strength of brain rhythm. Intuitively, prompts containing more detailed instruction related to the task could inform the users more precisely and vividly and hopefully could alleviate the challenge of motor imagination. In this sense, we explored the electroencephalography (EEG) characteristics of performing motor imagery and motor execution under different motion speeds and different prompt types. Ten subjects were invited to participate in motor imagery (MI) and motor execution (ME) tasks of the left hand and right hand at seven different speeds with either audio prompt or GIF prompt. A hypothesis of a linear relationship between the modulation of alpha (8-12 Hz) and beta band (18-28 Hz) ERD/ERS and motion speeds were tested. The experimental results showed that motion speeds were not linearly correlated to relative EEG changes at the alpha and beta bands in the sensorimotor cortex. Different prompts are found to have an effect on EEG activities in alpha and beta bands across the scalp, especially at occipital and frontal areas. Compared with audio prompts, subjects performed tasks with significantly improved accuracy with the assistance of GIF instructions. The current results could provide meaningful guidance for a better MI-based BCI system design as well as the MI classification enhancement.