## 2 Materials and Methods
### Recording of Continuous Brainwaves (CBW)  
Based on the results of the aforementioned psychological JND experiments in relation to the spatial ITDG, we expect that brainwaves provide the most efficient and direct approach for addressing psychological complexities and simplifying observations of auditory stimuli. The reason behind adopting this approach has been elucidated in our previous studies [1; 2; 3; 4; 5; 6] on the effectiveness of EEG in sound field design. Individual differences are the greatest hindrance for sound field components responding to brainwaves. Therefore, it is necessary to adopt an experimental design that involves continuous and repetitive methods for statistical analyses. Therefore, the data of CBW derived by approximately ten participants and the averaged intendency of them is adoptive to the significant level [1; 2; 3; 4; 5; 6]. To date, salient components in a sound field, such as T60 and the ITDG of a first reflection and a direct sound, can yield decent correlations through statistical analyses of individual preferences [5; 6]. [PERSON] et al. [8] and [PERSON] [9] consolidated the psychological states and responses manifested through AEPs (auditory evoked potentials) across different frequency ranges. CBWs were recorded at prolonged analysis times and could demonstrate electrophysiological events from the inner ear to the central auditory pathway, which made it possible to record slow components of AEP over 500 ms, such as the response of T60 in an environment. The 8 to 13 Hz range, which corresponds to alpha waves produced when humans are relaxed, is the most suitable state for thought and creation, and the mass generation of these alpha waves can be collected. These auditory impulses of the brain are recorded as CBWs. Meanwhile, the method of brainwave recording is based on the International 10/20 system for placing scalp electrodes to identify the region from where a specific psychological response is emitted [36; 37; 38]. When consolidating and reporting on brainwave signals from a statistical perspective, [PERSON], [PERSON], and [PERSON] [39] revealed that the application of spectral analysis would obliterate the characteristics of omnipresent brainwave changes because a spectrum, on average, is merely a single event. In this regard, we used [PERSON]'s (Section 5.4.2 in Ref. [17]) auditory pathway model to describe our approach for analyzing the omnipresent temporal characteristics of CBWs. Similar to experiments on the perceived JND of a spatial ITDG, it was necessary to simultaneously record CBWs through continuous cueing and the auditory stimuli, so as to make preparation for postproduction (as shown in Figure 4). Brainwaves from the cranial nerves were led through the primary electrodes (T3-left, T4-right, 10/20 system), which were correspondingly placed on the scalp. Meanwhile, the reference potential was recorded through the electrodes that were placed on both ear lobes (A1, A2), enabling the recording of cue sound signals via an EEG that used unipolar leads. The reference electrodes were positioned on both the left and right earlobes. The ground electrode was placed on the forehead. The CBW signals were analyzed after passing through a digital bandpass filter with cut-off frequencies (140 dB/octaves lops) of 8-13 Hz: alpha-wave ranges by Galileo Nemus space channel EEG system. Twelve subjects (students with an average age of 18 \(\pm\) 1.3 years old), all of whom self-reported as being right-handed and having normal hearing, all participated in the JND experiments before within a time period of less than 24 h. The number of participants demanded that the CBW recordings referred to conventional studies [1; 2; 3; 4; 5; 6], and [PERSON] and et al. [11] employed 7 subjects for the magnetoencephalographic (MEG) investigation, which met the requirements for analyzing CBW with respect to the sound field characteristics.