## 2 Background of This Research
### Tone Cognition and Human Processing  
A study on Mandarin Chinese tone perception has shown that even advanced second-language learners who have sufficient knowledge of words have difficulty recognizing tones included in  
Figure 1: Four tones in Mandarin Chinese using five-level tone marks (the numbers on the left side show the relative pitch: 1. Bottom, 2. Low, 3. Mid, 4. High, 5. Top). polysyllables and sentences [22]. The differences between the target language and native languages and the individual cognitive ability determine the difficulty in learning tones. However, educational policies and awareness of tone and learning strategies can be modified, which is a major factor in improving the efficiency of tone acquisition. A study was conducted to compare the learning effects of using monosyllabe words with using disyllable words on the initial education of Mandarin Chinese tones [23]. The results show that using disyllable words in the initial education is much more effective in the acquisition of tone perception and pronunciation of monosyllabe words and disyllable words (18.75% to 45% improvement). Regarding the tone errors of Mandarin Chinese learners, a study shows that teaching the third tone as a \"dipping-rising tone\" may cause tone pronunciation errors [24]. Furthermore, there are tone errors due to ineffective learning strategies of the learners, such as learners who are confident or good at recognizing and imitating pitch learning tones as melodies or learners who concentrate on reading and writing without noticing the importance of tone that may lead to fossilized errors. According to our research [25], although Mandarin Chinese beginners were trained in tone knowledge, most of the learners could not distinguish tones in four-syllable Mandarin Chinese, even when we slowed down the speech speed. It is considered that the pronunciation practice by imitating words and phrases, which is a general learning method used in existing learning materials and related research, is not the best way to acquire tone. Learners with low tone cognitive ability are more likely to practice pronunciation without noticing their pronunciation errors and inappropriate learning strategies, and the pronunciation errors get fossilized over time. Therefore, we focused on tone recognition based on information processing in cognitive psychology [26], which uses computer information processing to approach or explain human information processing. In addition, we used machine learning, which increases in accuracy with large amounts and variations of training data to metaphorize how learners acquire categorical perceptions of Mandarin Chinese tones. Cognitive psychology aims to elucidate the human information processing (perception, memory, cognition, etc.). Human information processing has stages and includes the following three processes:  
1. Discovery--Be aware of information in the environment that was previously overlooked;
2. Memory--Make the information meaningful and store in short-term or long-term memory;
3. Modify--Modify the long-term memory (re-learn). We assume that tone learning is recognizing audio information based on the existing knowledge of learners [27]. The knowledge of tones, especially the visual symbols as shown in Figure 1, can greatly help learners to discover and memorize tones. Furthermore, it is considered that recognizing tones requires considering the shortness of sensory memory (about 1 second or 0.25 to 4 seconds) among the three stages of human memory: sensory memory, short-term memory, and long-term memory. In the theory of cognitive psychology and education, based on the fact that the mental resources that can be used for human information processing are quite finite, cognitive load theory [28] for effective use of human cognitive resources has been developed. Cognitive load can be classified into the following three categories in relation to learning. 1. Intrinsic cognitive load--Related to the learning content (difficulty of learning content);
2.