2. Model of Auditory Brain System

Four significant, orthogonal physical factors that describe temporal and spatial features of sound fields in concert halls have been specified (Ando Y, Concert hall acoustics. Springer, Heidelberg, 1985). Important qualities of sound in terms of neural information processing in the associated auditory pathways and the rest of the brain have been addressed accordingly. If enough were known about how the brain analyzes nerve impulses from cochlea to cortex, the design of concert halls and other acoustic environments could proceed rationally, according to guidelines derived from the knowledge of these processes. Formulation of such a neurally grounded strategy for inducing subjective preference (the most primitive response of an organism as discussed in the Preface) through apposite acoustic design has been initiated through the study of auditory-evoked electrical potentials such as the slow-vertex responses (SVR), which are generated by the left and right human cerebral hemispheres. The goal of these experiments has been to identify potential neuronal response correlates of subjective preference for the orthogonal acoustic parameters related to the perception of sound fields. Using the paired-comparison method (Ando Y, Subjective preference in relation to objective parameters of music sound fields with a single echo. J Acoust Soc Am 62:1436–1441, 1977; Calculation of subjective preference at each seat in a concert hall. J Acoust Soc Am 74:873–887, 1983; Concert hall acoustics. Springer, Heidelberg, 1985; Architectural acoustics, blending sound sources, sound fields, and listeners. AIP Press/Springer, New York, 1998), it had been established that particular ranges of the four orthogonal factors were preferred by most listeners. These factors and auditory-evoked potentials (AEPs) were integrated by the triggering technique, so that reliable predictions of subjective preferences could be made. Similarly, in the study, the SVR for paired stimuli was integrated, and scale values of subjective preference based on the paired-comparison method were obtained. The SVR is a response of the brain that occurs after the auditory brainstem response (ABR) and is assumed to be an extracted factor which correlates to subjective preference. Correlations between subjective preference and neuronal responses were found in the following: temporal factors of the sound field clearly indicated that reverberation patterns such as the initial time delay gap between the direct sound and the first reflection (Δt ₁) and subsequent reverberation time (T _sub) are deeply associated with the left hemisphere; in contrast, typical spatial factors of the sound field, the IACC, and the binaural listening level (LL) are associated with the right hemisphere (Table 2.1; Ando Y, Investigations on cerebral hemisphere activities related to subjective preference of the sound field, published for 1983–2003. J Temporal Des Archit Environ 3:2–27, 2003).