Two-step discrimination task

This was an AXB discrimination task. The participants heard three stimuli per trial and had to determine whether the second sound (X) was the same as the first (A) or the third sound (B). Just as Experiment 3, there were three subtests for the Mandarin participants: real words, nonce words, and pure tone, whereas the English participants only had one real word subtest.

5.3 Stimuli

The speech materials were the same stimuli as those in Experiment 3. There were also three kinds of stimuli: real words, nonce words, and pure tones, and they were distinguished and presented in different subtests. Three stimuli from the same continuum were played in a rowfor each trial. The first stimulus (A) and the third (B)for each continuum were two steps apart, so that there were six possible A-B pairs (step 0-step2, step 1-step 3, step 2- step 4, step 3-step 5, step 4-step 6, and step 5-step 7). In each trial, A and B corresponded to one two-step pair of a continuum, while the second stimulus (X) was identical to either A or B. As a consequence, the AXB trials had four possible combinations (AAB, ABB, BAA, and BBA). Nevertheless, in order to explore and compare the impact of the ascending, as well as the descending order, half of the participants only encountered AAB and ABB, while the other half were presented with BAA and BBA. In

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addition, the trials were organised in a pseudo-random order, making 36 trials (6 tone pairs x 3 syllables x 2 combination) for each participant in each subtest. The orders were created so that there were not more than two identical words after each other and more than one identical tone pair. Sixteen different lists were created in total. Three cartoon dinosaurs in different colours were shown on computer monitor to make the experiments more interesting to young children. The first sound (A) was produced by the red Dino on the left of the screen, the second (X) was made by the yellow Dino in the middle of the screen, and the third (B) by the blue Dino on the right of the screen. A Dino jumped when a sound was played. All the tasks were run on Mammoth software.

5.4 Procedure

Every participant was presented with three subtests: real words, nonce words, and pure tones, and the order of the three subtests were randomised. In this task, the participants heard three stimuli per trial along one continuum and were required to make a forced choice as to whether the second stimulus (X) sounded the same as the first (A) or the third (B). If the participants believed that the second sound (X) made by the yellow dinosaur in the middle of the screen was the same as the first stimulus (A) produced by the red dinosaur on the left of the screen, they should press the key Q. If they considered that the second stimulus (X) was the same as the third sound made by the blue dinosaur on the right of the screen, they should press the key P. No feedback was given in the main phase and the next trial was presented after each click.

6 Results of discrimination task

6.1 Mandarin results across stimulus types

The results across participants are displayed in Table 30. The percentages of correct responses were all above the chance level (50%) in all steps. As manifested in Figure 39 and 40, the lines were askew and the performance

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on the left was relatively higher than on the right. The accuracy rate was the highest at pair 0-2 and pair 1-3 (both around 90%), then became lower and lower along the continuum, and finally reached the bottom at pair 5-7 (73%). Mandarin NLP has higher percentages of correct responses than other four groups at pair 0-2 (93%), pair 1-3 (94%), and pair 5-7 (79%), while Mandarin OTD has higher percentages of correct responses than other four groups at pair 3-5 (88%) and pair 4-6 (84%). On the other hand, Mandarin SLP has lower percentages of correct responses than other four groups at pair 0-2 (84%) and pair 1-3 (82%), while Mandarin YTD has lower percentages of correct responses than other four groups at pair 2-4 (65%), pair 3-5 (64%), pair 4-6 (56%) and pair 5-7 (57%).

0-2 1-3 2-4 3-5 4-6 5-7 Mandarin ASD (n = 21) 0.88 0.87 0.83 0.76 0.73 0.71 Mandarin NLP (n = 7) 0.93 0.94 0.83 0.79 0.81 0.79 Mandarin SLP (n = 9) 0.84 0.82 0.88 0.77 0.74 0.68 Mandarin YNLP (n = 5) 0.91 0.86 0.65 0.64 0.56 0.57 Mandarin YTD (n = 10) 0.89 0.92 0.88 0.79 0.76 0.78 Mandarin OTD (n = 9) 0.91 0.92 0.85 0.88 0.84 0.73 Overall (n = 40) 0.89 0.90 0.84 0.80 0.77 0.73 Table 30. Percentage of correct responses of two-step discrimination across stimulus type for each Mandarin group

In order to further explore if various groups would behave differently in this task, whether there is a significant effect of the steps, and whether there is a correlation between the groups and the steps, a mixed ANOVA was performed with a within-subject factor, Step (step 0-2, step 1-3, step 2-4, step 3-5, step 4-6, step 5-7), and a between-subject factor Group (Mandarin ASD, Mandarin TD). There was no effect of Group F (1, 34) = 1.443, p =

160 .238, η2

= .041, but here was a main effect of Step F (5, 170) = 12.994, p < .001, η2 _{= .276. Bonferroni post-hoc tests indicated that the performance at}

step 0-2 was significantly higher than the performance at step 3-5 (p = .008), step 4-6 (p = .003), and step 5-7 (p = .001). In addition, the performance at step 1-3 was significantly higher than the performance at step 3-5 (p < .001), step 4-6 (p < .001), and step 5-7 (p < .001). Further, the performance at step 2-4 was significantly higher than the performance at step 5-7 (p = .015). There was no interaction between the within-subject factor, Step, and the between-subject factor, Group F (5, 170) = .340, p = .888, η2

= .010.

Figure 39. Two-step discrimination curves across stimulus type for Mandarin ASD and Mandarin TD

A mixed ANOVA was performed with a within-subject factor, Step (step 0- 2, step 1-3, step 2-4, step 3-5, step 4-6, step 5-7), and a between-subject factor Group (Mandarin NLP, Mandarin SLP, Mandarin YNLP, Mandarin YTD, Mandarin OTD). There was no effect of Group F (4, 31) = 1.244, p = .313, η2

= .138, but here was a main effect of Step F (5, 155) = 14.846, p < .001, η2

= .324. Bonferroni post-hoc tests indicated that the performance at step 0-2 was significantly higher than the performance at step 3-5 (p = .001), step 4-6 (p < .001), and step 5-7 (p = .001). In addition, the performance at step 1-3 was significantly higher than the performance at step 3-5 (p < .001), step 4-6 (p < .001), and step 5-7 (p < .001). Further, the

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performance at step 2-4 was marginally higher than the performance at step 5-7 (p = .053). There was no interaction between the within-subject factor, Step, and the between-subject factor, Group F (20, 155) = 1.247, p = .224,

η2

= .139.

Figure 40. Two-step discrimination curves across stimulus type for Mandarin NLP, Mandarin SLP, Mandarin YNLP, Mandarin YTD, and Mandarin OTD

6.2 Breakdown of Mandarin results for the three stimulus types