The University of Melbourne

Field W Rickards

Lawrence Thomas Cohen

John Charles Parker

An evoked response audiometer method and apparatus in which a patient receives an auditory stimulus signal comprising a carrier frequency which is periodically amplitude modulated and frequency modulated whereby the stimulus is at least substantially frequency specific, the brain potential signals of the patient evoked by the auditory signal being sampled to determine whether phase locking to the modulated auditory signal has occurred, the auditory signal being selectively controlled to advance or delay one modulation with respect to the other modulation to cause enhancement of the evoked response to the auditory stimulus.

Phase lock evoked response audiometer

An evoked response audiometer for sleeping subjects comprising a function generator for supplying to a sleeping patient an auditory signal consisting of a carrier frequency which is periodically modulated at frequencies in excess of 60 Hz, the frequency of modulation being varied in a generally increasing manner for auditory signals of higher frequencies such that the stimulus is frequency specific, a detector for sampling and analyzing brain potentials evoked by said signal, a low-pass filter providing a time window which samples the brain potentials for a predetermined interval to provide sets of fourier analysis samples containing amplitude and phase data in narrow bands centered on the modulation frequency and its second harmonic, a computer for analyzing the Fourier analysis samples to extract means values of the amplitudes and phase angles of the signals, and for extracting from the means values of the phase angles the probabilities that the distributions of the phase angles could have occurred by change, whereby the existence of phase locking of the brain potential signals can be determined.

Evoked response audiometer for testing sleeping subjects

An evoked response audiometer is disclosed in which the patient is presented with a continuous auditory signal which is amplitude modulated and the evoked brain potentials of the patient (EEG) are recorded. The potentials are amplified and filtered and are averaged over a number of sampling periods to improve the signal to the noise ratio. The averaged signals are then analyzed to determine the amplitude and phase of the main components of the response to determine whether phase locking has occurred. The phase of the main components is then plotted against variation of the modulating frequency and the gradient of the plot provides the latency of the response from which neurological and other factors of significance to the hearing of the patient may be determined. The sound pressure level of the auditory signal is also varied and the amplitude and phase of the response plotted against these changes to provide an indication of the sensitivity of the hearing of the patient.

Growing community of inventors

Melbourne, Australia

Field W Rickards