## 2 Materials and Methods
### EEG Recording and Analysis  
EEG signals are recorded using Emotiv-EPOC to collect continuous brain waves. Electrodes are placed at the frontal (AF3, AF4, F3, F4, F7, F8, FC5, FC6), temporal (T7 and T8), parietal (P7 and P8), and occipital (O1 and O2) regions, along with two reference electrodes (CMS/DRL located at P3 and P4). For this experiment, eight electrodes, including AF43, AF4, F3, F4, F7, F8, FC5, and FC6, were focused on the frontal region to be observed, as illustrated in Figure 2. Their placement corresponds to the international 10-20 electrode placement system. The device complied with safety standards for radio frequency emissions and electrical safety. Permission for this trial was obtained by Dr. Moewardi General Hospital under research ethics code No. 1203/IX/HERC/2022. EEG signals are recorded in the form of signals in the time domain, while to obtain alpha, beta, and theta waves, it is necessary to know the frequency of the signal. To convert a time domain into a frequency domain, signal processing is required to convert the signal. A method that can be used to obtain frequencies is based on spectrum estimation calculations using power spectrum density (PSD) [57; 58; 59]. PSD is a measure of how strong brain activity is at various frequencies. It is calculated by squaring the magnitude of the Fourier transform and is usually calculated for a specific time interval [55; 60; 61]. The results of PSD calculations can be visualized in graphic form. The PSD graph shows the intensity of brain activity in various frequency ranges. An Emotiv-EPOC with 14 electrodes which were wet via saline was used to collect the continuous brain waves. The electrodes are mounted at the frontal (AF3, AF4, F3, F4, F7, F8, FC5, and FC6), temporal (I7 and T8), parietal (P7 and P8), and occipital (O1 and O2) regions, along with two reference electrodes (CMS/DRL located at P3 and P4). Different cognitive states correspond to different indicators, some being controversial due to different experimental tasks [35; 62]. In this study, after reviewing the relevant literature, three indicators were selected as cognitive performance measurement metrics, namely the cognitive aspects of attention measured based on the prefrontal beta signals of the AF3, AF4, F3, and F4 channels, stress aspects measured based on the alpha lateral frontal cortex signals of the F7 and F8 channels, and the mental workload aspects based on the theta/alpha ratios of the AF3, AF4, F3, F4, F7, F8, FC5, and FC6 channels [35; 62; 63]. The experimental research design is shown in Figure 3. The EEG device used is the EEG Emotiv EPOC X (Emotiv, San Francisco, CA, USA), which has 14 channels with a sampling rate of 128 Hz. A bandpass filter (1-30 Hz) is used to record EEG data, the raw data is recorded using Emotiv Pro software (Version 3.0), and raw data preprocessing is done using EEGLAB (Version 2023) on MATLAB (Version R2021a) ToolBox. The data processing of a set of net EEG data involves feature extraction and classification. EEGLAB STUDY is used in the data processing step of EEGLAB. EEGLAB STUDY is a feature to statistically analyze and process the input data from EEG signals. The processing output using EEGLAB STUDY in this study shows the power spectrum at alpha, beta, and theta frequencies as well as topography when subjects were treated to each type of noise and noise level. Power spectrum density (PSD) in the context of an electroencephalography (EEG) signal is a representation of the distribution of energy or signal strength at various frequencies. PSD EEG signals measure the strength or amplitude of the brain's electrical activity over a wide range of frequencies. The PSD analysis of EEG signals involves the process of transforming time-domain signals into frequency domains using the Fourier transform method.