Autocorrelation analyses of magnetoencephalographic alphawaves in relation to subjective preference for a £ickering light Yoshiharu Soeta, CA Yosuke Okamoto, Seiji Nakagawa, 1 MitsuoTonoike 1 and Yoichi Ando GraduateSchoolofScienceandTechnology,KobeUniversity,Rokkodai,Nada,Kobe657-8501; 1 LifeElectronicsLaboratory, NationalInstituteofAdvancedIndustrialScienceandTechnology,AIST,Midorigaoka,Ikeda,Osaka,563^8577,Japan CA CorrespondingAuthor Received18January2002;accepted21January2002 Humancorticalresponsescorrespondingtothesubjectiveprefer- ence for a £ickering light of varying period were investigated. Paired-comparison tests wereperformed to examine the subjec- tivepreferencefora£ickeringlight,andMEGwasrecordedduring presentations of the mostpreferred andless preferred £ickering lights alternately. Results showed that the e¡ective duration of theautocorrelationfunction, t e ,whichrepresentsarepetitivefea- tureoftheMEGalphawaves,becomeslongerduringthepreferred condition. This reveals that the brain repeats a similar rhythm under preferred conditions. NeuroReport 13:527^533  c 2002 LippincottWilliams&Wilkins. Keywords: Alphawave;Autocorrelationfunction(ACF);E¡ectivedurationoftheACF(t e );Magnetoencephalography(MEG);Subjectivepreference INTRODUCTION Some researchers have found that the autocorrelation function (ACF) of EEG alpha waves has a strong corre- spondence with subjective preference. Concerning auditory sensation, the relationships between the ACF of EEG alpha waves and subjective preference of the initial time delay between the direct sound and the first reflection (Dt 1 ) [1,2], subsequent reverberation time (T sub ) [3], or tempo of noise bursts have been investigated [4]. The factors Dt 1 and T sub are two of four factors for evaluating and designing sound fields for concert halls and opera houses. These results clearly indicated that the effective duration of the normal- ized ACF envelope, t e , one of the typical temporal factors, is significantly larger for a preferred stimulus than for a non- preferred one on only the left hemisphere. Also, the results showed that hemispheric specialization for Dt 1 and T sub indicates left hemisphere dominance. The relationship between the ACF of EEG alpha waves and subjective preference for a flickering light has also been investigated with regard to visual sensation [5]. These results also indicated that the t e values of the ACF are significantly larger for a preferred stimulus than for a non-preferred one. However, hemispheric specialization was not found. Visual cortices of the left and right hemispheres are close in position and are not clearly distinguished compared to the auditory cortex. In addition, an EEG measured on the scalp could be distorted due to various inhomogeneities of the head. MEG, in contrast, is produced by currents less subject to distortion because they flow through the relatively homogeneous intracranical space. Therefore, we can logi- cally assume that the left hemisphere dominance of the temporal factors of visual stimuli may be more clearly reflected in an MEG than in an EEG. To investigate human cortical responses that correspond to subjective preference and hemispheric specialization for visual stimulus, we analyzed the ACF of MEG in relation to the period of a flickering light. We chose subjective preference as a primitive response that would lead the individual away from inappropriate environments and toward desirable ones [6]. MATERIALS AND METHODS Subjective preference test: The light source was a 7 mm diameter green LED, set at a distance of 1.0 m from the subject in the center of the visual field in dark surroundings. The stimulus field from the LED was spatially uniform and its size corresponded to 0.41 of visual angle. Stimulus waveforms were generated by a computer with a 16-bit digital-to-analog converter. The parameters are shown in Fig. 1. The luminance of the stimulus is given by LðtÞ¼ L 0 ½1 þ m cosð2pftÞ, ð1Þ where L 0 is the mean luminance, m is the relative amplitude of modulation (fixed at 1.0), and f is the temporal frequency of the stimulus. The period of the stimulus, T ¼ 1/f, was set 0959-4965  c LippincottWilliams&Wilkins Vol13 No 4 25 March 2002 527 CLINICALNEUROSCIENCE ANDNEUROPATHOLOGY NEUROREPORT