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The use of phase in the detection of auditory steady-state responses
T W Picton1, A Dimitrijevic, M S John
1Rotman Research Institute, Baycrest Centre for Geriatric Care, University of Toronto, 3560 Bathurst Street, Toronto, Ontario, Canada M6A 2E1. tpicton@rotman-baycrest.on.ca
Objective:
To investigate how phase measurements might facilitate the detection of auditory steady-state responses.
Methods:
Multiple steady-state responses were evoked by auditory stimuli modulated at rates between 78 and 95 Hz and with intensities between 50 and 0 dB SPL. The responses were evaluated in 20 subjects after 1, 2, 4, and 6 min. The responses were analyzed in the frequency domain using 4 different detection protocols: (1) phase-coherence, (2) phase-weighted coherence, (3) F test for hidden periodicity, and (4) phase-weighted t test. The phase-weighted measurements were either based on the mean phase of a group of normal subjects or derived for each subject from the phase of the response at higher intensities.
Results:
Detection protocols based on both phase and amplitude (F test and phase-weighted t test) were more effective than those based on phase alone (phase coherence and phase-weighted coherence) although the difference was small. Protocols using phase-weighting were more effective than those without phase-weighting. The lowest thresholds for the steady-state responses were obtained using the phase-weighted t test.
Conclusion:
Threshold detection can be improved by weighting the detection protocols toward an expected phase, provided that the expected phase can be reliably predicted.