Intercept points

The intercept points were calculated based on the linear functions of individual of identification curves. It was the point at the chance level, where 50% of the responses identifying the stimuli as Tone 1, and 50% of the responses were naming the stimuli as Tone 4. For example, if a participant had 50% of T4 responses at step 2, then the intercept point for this participant would be 2. If a participant had 40% of T4 responses at step 2 and 60% of T4 responses at step 3, then the intercept point for this individual would be 2.5.

A mixed ANOVA was performed with one within-subject factor, Stimulus (Real word, Nonce word, Pure tone), and one between-subject factor, Group (Mandarin NLP, Mandarin SLP, Mandarin YNLP, Mandarin YTD, Mandarin OTD) on the dependent variable, Intercept. (The data of Mandarin KTD is not included because they were only tested on the real word stimuli.) There was a marginal effect of Group F(4, 32) = 2.423, p = .068, η2

= .232, but Bonferroni post-hoc tests did not reveal any significant difference between the five groups. There was a main effect of Stimulus F(2, 64) = 8.905, p < .001, η2

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that the intercept of nonce words was significantly higher than that of real words (p = .015) and pure tones (p = .002). There was no interaction between the within-subject factor, Stimulus, and the between-subject factor, Group F(8, 64) = .861, p = .554, η2

= .097.

Figure 26. Means of intercept points for each stimulus type for four Mandarin groups (Mandarin NLP, Mandarin SLP, Mandarin YNLP, Mandarin YTD, Mandarin OTD)

Now we would like to focus on the analysis of real words, so that the data of Mandarin KTD as well as English participants could also be included in the following seven tests on the intercept points.

A one-way ANOVA was performed to explore the effect of the between- subject factor, Group (Mandarin NLP, Mandarin SLP, Mandarin YNLP, Mandarin YTD, Mandarin OTD, Mandarin KTD) on the dependent variable, Intercept, in real word conditions. The results revealed a main effect of Group F(5, 52)= 3.585, p = .007. Bonferroni post-hoc tests revealed the intercept of Mandarin YNLP was significantly lower than that of Mandarin SLP (p = .005) and Mandarin KTD (p = .032)

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Figure 27. Means of intercept points for real word for five Mandarin groups (Mandarin NLP, Mandarin SLP, Mandarin YNLP, Mandarin YTD, Mandarin OTD, Mandarin KTD)

A one-way ANOVA was performed to explore the effect of the between- subject factor, Group (Mandarin ASD, Mandarin TD) on the dependent variable, Intercept, in real word conditions. The results did not reveal a main effect of Group F(1, 56) = .744, p= . 392.

Figure 28. Means of intercept points for real word for Mandarin ASD and Mandarin TD

A one-way ANOVA was performed to explore the effect of the between- subject factor, Group (English NLP, English SLP, English YTD, English

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OTD) on the dependent variable, Intercept, in real word conditions. There was no main effect of Group F(3, 28) = 1.110, p = .362.

Figure 29. Means of intercept points for real word for four English groups (English NLP, English SLP, English YTD, English OTD)

A one-way ANOVA was performed to explore the effect of the between- subject factor, Group (English ASD, English TD) on the dependent variable, Intercept, in real word conditions. There was no main effect of Group F(1, 30) = .859, p = .362.

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Figure 30. Means of intercept points for real word for English ASD and English TD

A one-way ANOVA was performed to explore the effect of the between- subject factor, Group (Mandarin ASD, Mandarin TD, English ASD, English TD) on the dependent variable, Intercept, in real word conditions. There was no main effect of Group F(3, 86) = .881, p = .454.

Figure 31. Means of intercept points for real word for Mandarin ASD, Mandarin TD, English ASD, and English TD

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subject factor, Group (Mandarin ASD, English ASD) on the dependent variable, Intercept, in real word conditions. There was no main effect of Group F(1, 35) = .097, p = .757.

Figure 32. Means of intercept points for real word for Mandarin ASD and English ASD

A one-way ANOVA was performed to explore the effect of the between- subject factor, Group (Mandarin TD, English TD) on the dependent variable, Intercept, in real word conditions. There was a marginal effect of Group F(1, 51) = 3.154, p = .082.

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Figure 33. Means of intercept points for real word for Mandarin TD and English TD

3.5 Slopes

The slopes were also calculated based on the linear functions of individual of identification curves. We mainly focused on the slopes which crossed the chance level (50%). If the intercept point of a particular participant was 2.5, meaning the chance level was between step 2 and step 3, then the slope would be the actual number of T4 responses at step 3 minus that of at step 2. If the intercept point of an individual was 2, meaning that the chance level was just on step 2, then the slope would be the average of the actual number of T4 responses at step 3 minus that of at step 2, and the actual number of T4 responses at step 2 minus that of at step 1.

A mixed ANOVA was performed with one within-subject factor, Stimulus (Real word, Nonce word, Pure tone), and one between-subject factor, Group (Mandarin NLP, Mandarin SLP, Mandarin YNLP, Mandarin YTD, Mandarin OTD) on the dependent variable, Slope. (Once again the data of Mandarin KTD is not included because they were only tested on the real word stimuli.) There was no main effect of Group F(4, 31) = .593, p = .671,

η2

= .071, and there was no main effect of Stimulus F(2, 62) = 1.135, p = .328, η2

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Stimulus, and the between-subject factor, Group F(8, 62) = .866, p = .550,

η2 _{= .100.}

Figure 34. Means of slope for each stimulus type for four Mandarin groups (Mandarin NLP, Mandarin SLP, Mandarin YNLP, Mandarin YTD, Mandarin OTD)

Now we would like to focus on the analysis of real words, so that the data of Mandarin KTD as well as English participants could also be included in the following four tests on the slopes.

A one-way ANOVA was performed with a between-subject factor, Group (Mandarin NLP, Mandarin SLP, Mandarin YNLP, Mandarin YTD, Mandarin OTD, Mandarin KTD) on the dependent variable, Slope, for the data of real word. There was no main effect of Group F(5, 52) = .810, p = .548.

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Figure 35. Means of slope for real word for five Mandarin groups (Mandarin NLP, Mandarin SLP, Mandarin YNLP, Mandarin YTD, Mandarin OTD, Mandarin KTD)

A one-way ANOVA was performed with a between-subject factor, Group (English NLP, English SLP, English YTD, English OTD) on the dependent variable, Slope, for the data of real word. There was no main effect of Group F(3, 28) = .857, p = .475.

Figure 36. Means of slope for real word for four English groups (English NLP, English SLP, English YTD, English OTD)

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(Mandarin, English participants) on the dependent variable, Slope, for the data of real word. There was no main effect of Group F(1, 88) = 1.637, p = .204.

Figure 37. Means of slope for real word for Mandarin and English groups

A one-way ANOVA was performed with a between-subject factor, Group (Mandarin ASD, Mandarin TD, English ASD, English TD) on the dependent variable, Slope, for the data of real word. There was no main effect of Group F(3, 86) = .775, p = .511.

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Figure 38. Means of slope for real word for Mandarin ASD, Mandarin TD, English ASD, and English TD

4 Discussion of naming task results

Categorical perception of lexical tones

Q1: Do Mandarin-speaking children with autism spectrum disorder (ASD) categorically perceive and identify lexical tones in the same way as their typically-developing (TD) Mandarin-speaking counterparts, or do Mandarin-speaking ASD children perceive lexical tones in a psychophysical way?

The forced-choice identification task for Mandarin participants showed that Mandarin ASD did not perform significantly differently in the identification of Mandarin lexical tones from Mandarin YTD and OTD (Figure 18). These three groups all had low proportion of T4 responses at step 0 and step 1, then had a sharp slope and reached around 50% of T4 responses at step 2, and finally had high percentage of T4 responses at step 3, step 4, step 5, step 6, and step 7. This suggested that the Mandarin ASD and TD both perceived the lexical tones in a categorical way instead of a psychoacoustic way (Figure 17 and Table 27).

Nevertheless, since the data of ASD group were heterogeneous, we once again split it into Mandarin NLP and Mandarin SLP for further investigations (Figure 24). It turned out that the identification of lexical tones in Mandarin NLP was significantly different from that of in Mandarin SLP and Mandarin YTD. Just as indicated in Table 27 and Figure 19, Mandarin NLP had higher proportions of T4 responses than other groups for every step except step 0, suggesting that they were more inclined to label an item with pitch contours along the T1-T4 continuum as Tone 4 instead of Tone 1. Moreover, the proportions of T4 responses for step 5, 6, and 7 were almost 100%, indicating that Mandarin NLP categorized these steps altogether as Tone 4.

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On the other hand, the percentage of T4 responses in Mandarin SLP was significantly higher than Mandarin YTD, and marginally higher than Mandarin NLP and OTD at step 0 (i.e. Tone 1). Except for this, the proportions of T4 responses in Mandarin SLP were consistently lower than which of Mandarin NLP. These results revealed that Mandarin SLP had more difficulty in identifying Tone 1 itself than other three groups. In addition, while Mandarin NLP tended to label an item with pitch contours along the T1-T4 continuum as Tone 4 instead of Tone 1, Mandarin SLP participants, just as Mandarin YTD participants, were less inclined to identify the items as Tone 4 along the tone continuum.

It is important to point out that Mandarin NLP and SLP might perceive the lexical tones differently, or they might just have certain preferences or take various strategies in identifying Tone 1 and Tone 4. While a less sharp falling in pitch contour was also considered to be Tone 4 by Mandarin NLP, it seemed that Mandarin SLP participants were stricter and more conservative for the classification of Tone 4.

Q1a: Are the intercept points around the same place for both Mandarin typically-developing and ASD participants?

The intercept points across stimulus types for Mandarin ASD (Mandarin NLP, Mandarin SLP, and Mandarin YNLP) and TD (Mandarin YTD and Mandarin OTD) were both around step 2 and only showed a marginal difference between groups (Figure 26). However, the intercept points for real word (Mandarin KTD was also included) were significantly lower in Mandarin YNLP than in Mandarin SLP as well as Mandarin KTD (Figure 27).

Q1b: Are the slopes at the category boundary significantly different for Mandarin typically-developing and ASD participants?

The slopes across stimulus types for Mandarin ASD and TD (Mandarin YTD and Mandarin OTD) were both around 3 and did not show any

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statistical difference (50). In addition, although the slope for real word in Mandarin SLP was slightly lower than other Mandarin groups including KTD, there was still no statistical significance.

Role of native language

Q2: According to the literature, speakers of a tone language have a categorical perception of their native lexical tones, whereas speakers of a non-tone language perceive and process their lexical tones in a psychophysical way. Do Mandarin- and English-speaking participants perceive lexical tones differently, as suggested in the literature?

The AXB identification task for English participants showed that English ASD did not perform significantly differently in the identification of non- native lexical tones from English TD. There was a significant correlation between the Mandarin and the English participants. Just as shown in Figure 37, although the slopes around the category boundary in Mandarin group was not much steeper than in English participants, the percentage of T4 responses at step 0 and step 1 was significantly lower in Mandarin than in English participants. Therefore, while the slopes around the category boundary in Mandarin group was not significantly sharper than in English participants, the slopes along the tone continuum were actually significantly steeper in Mandarin than in English participants. This suggested that the Mandarin listeners tended to identify the native lexical tones in a more categorical way, and the English individuals perceived the non-native lexical tones in a more continuous way. The similar pattern was also found in the significant interaction between Mandarin TD and English TD. Although the results of Mandarin ASD and English ASD were not that clear and neat as the TD groups and did not have significant interaction, it could still be observed that the identification curve along the tone continuum in English ASD was less sharp than which of in Mandarin ASD (Figure 24 and 25).

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Q2a: Are intercept points around the exact centre of the tonal continuum or at a different point for Mandarin and English participants?

English ASD and English TD both had an intercept point around step 2 and did not differ significantly (Figure 30). While the intercept points in Mandarin overall participants and English overall participants were not significantly different, the intercept point in Mandarin TD was marginally higher than in English TD.

Q2b: Are the slopes at the category boundary significantly different for Mandarin and English participants?

English ASD and English TD both had a slope around 3.5 and did not differ significantly (Figure 38). In addition, although the slope for real word was slightly higher in English participants than in Mandarin participants (including KTD), this was not statistical significant. Nevertheless, as discussed in Q2, while the slopes of category boundary did not differ in Mandarin and English groups, the slopes along the continuum were actually significantly sharper in Mandarin than in English individuals. It would be more precise to explore the slopes along the tone continuum rather than only in the category boundary.

Role of stimulus type (real word, nonce word, pure tone)

Q3: Do ASD children and their controls identify the pitch contours of different kinds of stimuli (real words, nonce words, and pure tones) differently? Is there any interaction between the group and type of stimulus?

Mandarin ASD and Mandarin TD both behaved differently for different kinds of stimuli. Generally speaking, Mandarin participants had the highest percentage of T4 responses for pure tone, then for real word, and the lowest for nonce word. However, there was a significant interaction between the group and type of stimulus, which suggested that certain groups might

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behave differently in identifying these three stimulus types. The post-hoc tests revealed Mandarin ASD and OTD both had significantly higher percentage of T4 responses for pure tone than for nonce word. On the other hand, Mandarin YTD had significantly higher percentage of T4 responses for pure tone than for nonce word as well as real word. As shown in Figure 21 and 22, this could be attributed to the particularly high percentage of T4 responses for pure tone in Mandarin YTD.

Q3a: Do the different groups of participants categorically perceive nonce words and pure tones equally strongly as real words? Do they have the same intercept points, the same slopes at the intercept points, and the same enhanced perception at the category boundary of nonce word, pure tone, and real word stimuli?

Just as discussed above, the overall Mandarin data showed that the percentage of T4 responses was significantly higher in pure tone than in real word than in nonce word along the tone continuum (Figure 20). Overall, it is easier to perceive and discriminate the pure tones in the categorical perception naming test, since the participants could focus on the auditory pitch without the distraction of linguistic information. As for the real words and nonce words, although they both provide auditory pitch as well as linguistic information for discriminating the tones, it turned out that the real words are more helpful in the way that the participants have already learnt and categorized the real words in their lexicon.

On the other hand, these three stimulus types all had similar main effect of Step. That is, step 0 and 1 could be considered being within one category, whereas step 3, 4, 5, 6, and 7 could be categorized together. Therefore, Mandarin ASD and TD generally perceived these three kinds of stimuli in a categorical way.

Mandarin ASD and TD groups both had higher intercept points of nonce word than that of real word and pure tone. However, the slopes did not differ between these three stimulus types.

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5 Method of Task 2: Two-step discrimination task

5.1 Participants

The same Mandarin- and English-speaking participants as in the previous experiment participated in the current task.