1. Dept. of Veterans Affairs Puget Sound Health Care System Seattle, WA 98108, USA, Dept. of Electrical Engineering University of Washington Seattle, WA 98195, USA
2. Dept. of Veterans Affairs Puget Sound Health Care System Seattle, WA 98108, USA, Dept. of Rehabilitation Medicine University of Washington Seattle, WA 98195, USA
3. Dept. of Electrical Engineering University of Washington Seattle, WA 98195, USA