Predictability of Brain-Computer Communication

Abstract

Abstract Since 1996 we have been teaching more than 18 severely or totally paralyzed patients to successfully control the movements of a cursor on a computer screen by means of systematic changes in the amplitudes of their slow cortical potentials (SCPs; Birbaumer, Ghanayim, Hinterberger, Iversen, Kotchoubey et al., 1999 ). Patients learned regulation of their SCP amplitudes by means of a brain-computer interface (BCI) and on-line feedback about the time course of SCP amplitude shifts, represented by cursor movements on a computer screen. When patients were able to successfully regulate their SCP amplitude, they were trained to use this ability to communicate with friends and caregivers by means of a Language Support Program ( Perelmouter, Kotchoubey, Kübler, Taub, & Birbaumer, 1999 ). Having a reliable predictor of progress in training would be particularly helpful because training patients at their homes requires substantial effort and a positive outcome is desirable given limited personal and financial resources. In this study we present data from healthy participants (n = 10) and a sample of patients (n = 10), diagnosed with amyotrophic lateral sclerosis, who participated in six BCI training sessions; six patients continued training for another six sessions. All participants except one achieved stable significant cursor control. The number of sessions needed to achieve significant cursor control (initial training phase) correlated moderately with the number of sessions needed to achieve a correct response rate of 70% (advanced training phase). Individual differences in performance remained stable within the six training sessions. After six sessions both groups had achieved significant cursor control, but patients' performance was poorer than that of healthy participants. The patients, however, were trained once a week only, and for some patients longer breaks in training occurred. We conclude that learning during the initial training phase indicates the duration of training that will be necessary to achieve 70% correct responses. A higher frequency of training sessions per week seems necessary to achieve faster progress.