J. Temporal Des. Arch. Environ. 5(1), December 2005 Soeta et al. 5 Magnetoencephalographic activities related to the magnitude of the interaural cross-correlation function (IACC) of sound fields Yoshiharu Soeta, Seiji Nakagawa and Mitsuo Tonoike a) Institute for Human Science and Biomedical Engineering, National Institute of Advanced Industrial Science and Technology (AIST), Midorigaoka, Ikeda, Osaka, 563-8577 Japan (Received 18 December 2004; accepted 24 June 2005) Magnetoencephalographic (MEG) responses to the magnitude of the interaural cross-correlation function (IACC) of a sound field were investigated. The source signal was the word "piano", which had a 0.35-s duration. In MEG measurements, combinations of a reference stimulus (IACC = 1.0) and test stimuli (IACC = 0.27, 0.61, and 0.90) were presented 50 times alternately at a constant 1.5-s interstimulus interval. The MEG responses evoked by each stimulus in the pair were integrated and recorded with a 122- channel whole-head neuromagnetometer and analyzed using an autocorrelation function (ACF) and a cross-correlation function (CCF). The results showed that the effective duration of ACF, τ e , and the maximum value of CCF, |φ(τ)| max , of MEG between 8-13 Hz become larger as the IACC decrease. Although subjective preference tests for the IACC of speech sound fields have not been conducted in the present study, the previous studies of subjective preference for sound fields have showed that lower IACC is preferred. Therefore the results indicate that the brain repeats a similar temporal rhythm over a wider area under preferred sound fields. Keywords: autocorrelation function (ACF), cross-correlation function (CCF), magnetoencephalography (MEG), magnitude of interaural cross-correlation function (IACC) 1. INTRODUCTION In the field of room acoustics, four orthogonal physical pa- rameters influencing subjective preference for sound fields have been reported: (1) listening level (LL), (2) delay time of a single reflection in reference to the direct sound, (Δt 1 ), (3) subsequent reverberation time (T sub ), and (4) the magnitude of the interaural cross-correlation (IACC) [1-3]. To investi- gate the relationship between brain activities and subjective preferences for sound fields, Ando and Chen [4], Chen and Ando [5] and Sato et al. [6] analyzed electroencephalography (EEG) with the autocorrelation function (ACF). The EEG frequency band between 8 and 13 Hz was analyzed by the effective duration of the envelope of the normalized ACF (τ e ) when the factors of sound fields, Δt 1 , T sub and IACC were varied. The results showed that the τ e of the EEG between 8- 13 Hz was significantly longer for the preferred conditions of these factors, Δt 1 , T sub and IACC. It has recently been re- ported that a τ e of a MEG between 8-13 Hz is strongly corre- lated with subjective preference for Δt 1 of speech [7]. τ e is defined as the time taken for the ACF envelope to reduce to ten percent of its original value, representing repetitive fea- tures within the signal itself. It has recently been found that the maximum amplitude of the cross-correlation function (CCF). |φ(τ)| max of a MEG between 8-13 Hz is correlated with subjective preference for the Δt 1 of speech [8]. ACF analysis concentrates on the intra-channel correlations, while CCF analysis concentrates on inter-channel correlations in the time domain. The purpose of this study was to examine the effects of the IACC on MEG responses when the sound source was speech. In previous studies on the relationship between brain activi- ties and subjective preference for sound fields, the sound source was a music motif and only the EEG or MEG fre- quency band between 8-13 Hz was analyzed. Here, speech was used as the sound source and other MEG frequency bands were also analyzed by the ACF and CCF. ISSN1346-7824 http://www.jtdweb.org/ a) Now at Faculty of Engineering, Chiba University, Inage-ku, Chiba 263-8522, Japan