## 2 Experimental Design
### Experiment 1: ACPT in a Noisy Environment  
1 Experimental environment  
The experimental scenario was selected to be conducted in an anechoic chamber, as shown in Figure 1. The fully anechoic chamber has an area of 190 m\({}^{2}\), a volume of 1300 m\({}^{3}\), a background noise below N1, and a lower limit frequency of 50 Hz, which meets the requirements of the international standard ISO3745 for anechoic chambers.  
A total of 5 speakers are needed in the experiment, the speakers are placed in a 5-channel surround sound system. The listening point where the subject is located is regarded as the center of the circle. Each speaker is 2 m away from the listening point, according to the angle regulations, the speaker is placed on the circumference, and the radiation center of the speaker is 1.5 m away from the ground. The middle speaker plays speech signals, and the remaining four speakers play noise signals. The speaker placement is shown in Figure 2. The experimental signal playback is controlled by a computer and equipped with a multichannel sound card connected to a 16-channel digital mixer with a frequency response range of 20 Hz to 20 kHz.  
Figure 1: Anechoic chamber environment.  
Noise type and SNR  
Two typical types of noise, namely pink noise and speech noise, were selected for this experiment. Pink noise is the most common noise in nature, and its energy decays continuously from low to high frequencies, dropping 3 dB per octave in linear coordinates, which is the standard signal in measurement. Speech noise is one of the main sources of background noise in the classroom. Four girls and four boys recorded meaningful Chinese sentences in the recording room and then mixed them to form speech noise, thus simulating the noise environment in a normal classroom. The sound pressure level at the listening point was set to 65 dBA. Referring to a previous study [31], the signal-to-noise ratio was selected for 7 cases: \(-\)5 dB, 0 dB, 5 dB, 10 dB, 15 dB, 18 dB, and no noise. The same SNR was set for both noise interference experiments, with a total of 13 SNR conditions.  
Subjects  
A total of thirty Chinese college students (age: 22.4 \(\pm\) 0.9 years) participated in the experiment; they were able to speak standard Mandarin Chinese and had no cognitive impairment and normal hearing. All subjects received listening training.  
Procedure  
Before the formal test, subjects needed to practice in order to make the subjects familiar with the test software and the experimental procedure. The experiment was conducted using E-prime3.0 software, in which a computer was connected to a speaker to play the speech signals. The participants were presented with numbers from 1 to 50 in a random order through audio, and target stimuli were numbers with a unit digit containing 7, such as 7, 17, 27, 37, and 47, while the remaining numbers were distractor stimuli. Subjects were required to click the computer space bar when they heard the stimuli that met the requirements and to not respond if they did not meet the requirements. The digital signals were played randomly, with each digit lasting 600 ms with 1000 ms intervals in between. The total stimulus had 450 characters, and the target stimuli accounted for 20%. When the experiment was complete, the screen would display \"Experiment completed, thank you for your participation\". The experiment was conducted on one person at a time, and the duration of each test was approximately 12 min. In order to prevent the effects of practice and subject fatigue on the reliability of experimental results, the tests between each acoustic transmission condition needed to be separated by 2 weeks.  
Figure 2: Speaker placement.