A method of displaying the activity of a brain, the method including the steps of: (i) obtaining an electroencephalogram (EEG) signal from the brain (ii) segmenting said EEG signal into either contiguous or overlapping segments comprised of a sequential number of samples of said EEG signal (iii) representing said EEG segments as a fixed order autoregressive moving average (ARMA) signal representation with an autoregressive order between 8 and 13 and a moving average order between 5 and 1 1 (iv) rewriting in z-domain notation said fixed order ARMA signal representation to obtain a z-domain representation (v) generating AR coefficient data and MA coefficient data for said segments of said EEG signal for said fixed order ARMA signal representation: (vi) determining the poles and zeros of said z-domain representation for said segments of said EEG signal by substituting said coefficient data for said segments of said EEG signal into said z-domain representation (vii) calculating the sum of the number of poles determined in step (vi) (viii) calculating the sum of the number of zeros determined in step (vi) (ix) representing said ARMA signal representation as an infinite order autoregressive (AR) model in z-domain notation (x) determining autoregressive coefficient data for said infinite AR model from the AR and MA coefficient data generated in step (v) of said fixed order ARMA representation (xi) determining the sum of the poles for said infinite order AR model for said segments of said EEG signal as either: (a) the first autoregressive coefficient of said infinite order AR model or (b) the difference of the sum of poles and the sum of zeros as determined respectively in steps (vii) and (viii) (xii) determining an index value representing the activity of the brain for said segments of said EEG signal by applying a discriminating function to the sum of the poles of said infinite AR model for said segments of said EEG signal as determined in step (xi) and (xiii) displaying
