## 4 Discussion
### High Trajectories of T1 and T2
[40] with a difference of approximately 1 T-value for disyllabic words and 2 T-values for monosyllabic words. L1-dominant Polish speakers learning Mandarin (L2), on the other hand, maintain a tonal range of 4.25-2 T-values for monosyllabic words and 4-2 T-values for disyllabic words, showing a consistent 2 T-value difference between the two. This suggests that native Mandarin speakers tend to demonstrate tones in a relatively sloppy manner in disyllabic words, possibly because disyllabic words already carry meaning and native speakers do not necessarily need to articulate tones precisely to achieve communicative goals. Hence, tonal ranges are smaller in disyllabic words for native speakers. In contrast, ref. [49] reported that English native speakers at the HSK5 level exhibited smaller tonal ranges than the control group of native Mandarin speakers across three target syllables, indicating that L1-dominant Polish speakers learning Mandarin (L2) have adjusted their tonal ranges to approximate those of native speakers. For Japanese and Korean L2 learners, errors in T2 or T3 are particularly frequent when followed by T1 or T4, both of which are high-onset tones [16; 17]. These findings suggest that disyllabic words should be viewed as connected units rather than as combinations of two independent monosyllabics, inspiring our recommendation to practice tones in conjunction with T3. On the other hand, Polish speakers exhibit a significantly higher F0 range compared to German speakers [37; 38]. Additionally, in terms of perception, the loss of the speech spectrum below 350 Hz in Polish only results in a 2% reduction in speech clarity. This suggests that low-frequency sounds in speech are not particularly meaningful for Polish speakers. Therefore, we observe that due to the relatively smaller tonal range of native Mandarin speakers in disyllabic words, L1-dominant Polish speakers learning Mandarin (L2) tend to exhibit higher starting points in comparison. This results in subsequent higher tonal registers. To minimize the perceptual differences in tones between Polish learners and native Mandarin speakers, or to make Polish learners' pronunciation more similar to that of native speakers, we recommend that L1-dominant Polish speakers learning Mandarin (L2) practice reducing the pitch of each syllable in disyllabic words when in a high tonal register. This approach will make their pronunciation sound more natural and less like a sequence of individual monosyllabic words concatenated together into disyllabic words. Furthermore, we would explain to Polish learners that in disyllabic words, native speakers already perceive a meaningful combination of syllables, and precise tone articulation in every syllable, especially in high tonal registers, may not be necessary. Moreover, due to the differences in tonal range between Polish learners and native Mandarin speakers in monosyllabic and disyllabic words, tones such as T1 and T2 associated with high tonal registers are affected. This is often caused by starting pitches in disyllabic words being too high, leading to overall higher tonal contours, whether flat, rising, or falling, compared to native Mandarin speakers. The habit of using higher registers originates from the language transfer effects from Polish itself. To sum up, we suggest that L1-dominant Polish speakers learning Mandarin (L2) relax their vocal cords when pronouncing the first syllable of disyllabic words, avoiding excessively high pitch as the starting point. With practice, they can gradually approach the pronunciation of disyllabic words more closely to that of native Mandarin speakers. The problem is particularly relevant from the perspective of language learners who aim to achieve native-like production of non-native phonemes. This intention is closely associated with a large number of Mandarin learners whose native languages lack lexical tones.