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Neurorehabilitation Technology, ch. The human in the loop

  • Authors: Koenig, Alexander C.; Riener, Robert; Billard, Aude

In classical man-machine interfaces applied to rehabilitation, the primary goal is to control the (bio)mechanical interaction between the human and the machine or environment. However, integrating the human into the loop can be considered not only from a biomechanical view but also with regard to psychophysiological aspects. Biomechanical integration involves ensuring that the system to be used is ergonomically acceptable and “user cooperative.” Psychophysiological integration involves recording and controlling the patient’s physiological reactions so that the patient receives appropriate stimuli and is challenged in a moderate but engaging way without causing undue stress or harm. In this chapter, we present examples of biomechanical and psychophysiological integration of patients that have been verified with the gait robot Lokomat.

Posted on: March 22, 2012

Single trial prediction of self-paced reaching directions from EEG signals

  • Authors: Lew, Eileen Y.; Chavarriaga, Ricardo; Millán, José del R.

Early detection of movement intention could possibly minimize the delays in the activation of neuroprosthetic devices. As yet, single trial analysis using non-invasive approaches for understanding such movement preparation remains a challenging task. We studied the feasibility of predicting movement directions in self-paced upper limb center-out reaching tasks, i.e., spontaneous movements executed without an external cue that can better reflect natural motor behavior in humans. We reported results of non-invasive electroencephalography (EEG) recorded from mild stroke patients and able-bodied participants. Previous studies have shown that low frequency EEG oscillations are modulated by the intent to move and therefore, can be decoded prior to the movement execution. Motivated by these results, we investigated whether slow cortical potentials (SCPs) preceding movement onset can be used to classify reaching directions and evaluated the performance using 5-fold cross-validation. For able-bodied subjects, we obtained an average decoding accuracy of 76% (chance level of 25%) at 62.5ms before onset using the amplitude of on-going SCPs with above chance level performances between 875ms to 437.5ms prior to onset. The decoding accuracy for the stroke patients was on average 47% with their paretic arms. Comparison of the decoding accuracy across different frequency ranges (i.e., SCPs, delta, theta, alpha and gamma) yielded the best accuracy using SCPs filtered between 0.1 to 1 Hz. Across all the subjects, including stroke subjects, the best selected features were obtained mostly from the fronto-parietal regions, hence consistent with previous neurophysiological studies on arm reaching tasks. In summary, we concluded that SCPs allow the possibility of single trial decoding of reaching directions at least 312.5ms before onset of reach.

Posted on: July 7, 2014