**1. Introduction**

In human speech cognition, speech intelligibility integrates short-term memory and cerebral feedback [1]. However, important factors constituting the spatial impressions of sound also include certain related evaluation indicators, such as the listener's judgment of sound source direction (sense of direction) and distance (sense of proximity), apparent source width (ASW), and lateral envelopment (LEV). As suggested by Ando [2] and Beranek [3], the composition of such spatial impressions mainly depends on fluctuations of the magnitude of the interaural cross-correlation (IACC) and is especially affected by the degree of subjective diffusion of the sound field. However, listeners differ in their needs and perceptions regarding subjective diffusion and ASW.

With regard to neuron-psychology, Sperry [4] discovered the phenomenon of hemispheric disconnect. The cerebral specialization theory distinguishes between "speech functions" and "non-speech functions." Certain symbols in architectural

design belong to non-speech functions. For instance, the range of non-speech functions includes aesthetic perception and the feeling of balance. In particular, many non-speech symbols can be observed in environmental design. Earlier research on audio and cerebral correlations found that such common medical problems as aphasia and disturbances in tone judgment originate in the left cerebral hemisphere. Therefore, this study suggested that cerebral responses to speech and non-speech symbol in the physical environment effectively substitute for the semantic differences (SD) caused by age-related and cultural differences. Cerebral responses to communication stimuli are a direct cross-cultural and cross-age reference indicator, which is similar to the principle behind polygraph tests performed by police to examine physiological responses.

This study suggested that cerebral responses can be used to clearly and consistently examine responses to change in "speech functions" of the physical environment, or speech intelligibility, when designing a sound field. Ando [2] considered "speech functions" to be an important temporal factor and the result of autocorrelation function (ACF) evaluations in the brain. Therefore, the environmental effects of temporal factors were examined in this study based on the influence of speech intelligibility on the correlation between "subjective perceptions" and cerebral responses, which served as the basis for the objective design of an acoustic environment. Akita et al. [5] indicated that when the sensory information received by listeners is analyzed by brainwaves, this does not represent their direct experience of changes in the environment, but rather the interaction between physiology and the environment. This phenomenon is common in daily life. The intensity of cerebral evoked responses is the optimal evaluation tool [6]. Soeta et al. [7] studied the effects of sound source features on subjective psychological responses and cerebral responses measured by magnetoencephalography (MEG) and reported that at different delay times of reflection sounds (Δ*t*1 = 0, 5, 20, 60, and 100 ms) and 50 alternations, the ACF effective delay time of α-waves recorded by MEG indicated subjective preferences regarding sound fields. The methods used in this study can be summarized as follows:

