**Abstract**

The influence of indoor speech intelligibility and apparent source width (ASW) on the response of cortical brainwaves was studied using two variables, the time gap between direct and the first reflection (Δ*t*1, ms) and the initial (<80 ms) interaural cross-correlation function (IACCE3). Comparisons were performed based on autocorrelation function (ACF) of continuous brainwave (CBW) and slow vertex response (SVR). The results are: (1) the effective delay time of ACF (*τe*) of β-waves (13–30 Hz) in the left hemisphere under changes in Δ*t*1 was significantly and positively correlated with speech intelligibility (*p* < 0.001). (2) As ASW increased, the relative amplitude of left hemisphere *A* (P2-N2) tended to decrease (*p* < 0.05) in SVRs, while N2 latency tended to increase (*p* < 0.05); the lateral lemniscus in the auditory nerve was suggested to be the reactive site. (3) With regard to hemispheric specialization in brain, speech intelligibility, the main temporal factor, was found to be controlled by the left hemisphere. A subjective spatial factor, ASW, the relative amplitude of SVR was also found to decrease in the left hemisphere; nevertheless, they are coherent while the N2 latency of SVR significantly prolonged in both left and right hemisphere under changes in IACCE3.

**Keywords:** brainwaves, ACF, apparent sound width, speech intelligibility, subjective diffuseness, hemispheric specialization
