Steady - State Evoked Potentials Possibilities for Mental - State Estimation 0 - 55 3 , - - / P

The use of the human steady-state evoked potential (SSEP) as a possible measure of mental-state estimation is explored. A method for evoking a visual response to a sumof-ten sine waves is presented. This approach provides simultaneous multiple frequency measurements of the human EEG to the evoking stimulus in terms of describing functions (gain and phase) and remnant spectra. Ways in which these quantities vary with the addition of performance %asks (manual tracking, grammatical reasoning, and decision making) are presented. Models of the describing function measures can be formulated using systems engineering technology. Relationships between model parameters and performance scores during manual tracking are discussed. Problems of unresponsiveness and lack of repeatability of subject responses are addressed in terms of a need for loop closure of the SSEP. A technique to achieve loop closure using a lock-in amplifier approach is presented. Results of a study designed to test the effectiveness of using feedback to consciously connect humans to their evoked response are presented. Findings indicate that conscious control of EEG is possible. Implications of these results in terms of secondary tasks for mental-state estimation and brain actuated control are addressed. INTRODUCTION By using appropriate signal averaging techniques, it is possible to detect a response in the human electroencephalograph (EEG) to evoking stimuli. When the stimulus is sinusoidally modulated the result is called a steady state evoked potential (SSEP). Research in this area (Spekreijse, 1966; Regan, 1972; Wilson and O'Donnell, 1980) suggests that the SSEP may be a useful indicator for mentalstate estimation. Using a light stimulus modulated by a sum of sine waves, 131 https://ntrs.nasa.gov/search.jsp?R=19880013996 2018-03-09T18:17:50+00:00Z