The use of phase in the detection of auditory steady-state responses

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. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.