Figure 2 shows mean RTs of the schoolchildren with and without ASD to the six different stimuli, and Fig. 3 shows mean RTs of the 5- to 6-year-old preschool children participants with and without ASD to the six different stimuli. When the collected data were analysed by a 2 (with/without ASD, PARTICIPANT) × 2 (snake/flower, IMAGE) × 2 (preschool/school, AGE) ANOVA (analysis of variance), all of the three main effects were statistically significant (F (1, 36) = 16.553, p = 0.000246, ηG2 = 0.309 for PARTICIPANT; F (1, 36) = 6.9846, p = 0.01209, ηG2 = 0.00536 for IMAGE; F (1, 36) = 42.88, p = 0.000000013, ηG2 = 0.537 for AGE). By contrast, none of the interaction effects were significant. The interaction between PARTICIPANT and IMAGE was not significant (F (1, 36) = 1.34, p = 0.253, ηG2 = 0.00104). The interaction between PARTICIPANT and AGE was not significant either (F (1, 36) = 0.000174, p = 0.9895, ηG2 = 0.0000047), and neither was that between IMAGE and AGE (F (1, 36) = 0.308, p = 0.582, ηG2 = 0.000238). The interaction among PARTICIPANT, IMAGE and AGE was not significant (F (1, 36) = 0.0818, p = 0.777, ηG2 = 0.0000631).
Overall, children with ASD responded to the presented stimuli more slowly than the TD children regardless of age. In both of these participant groups, RTs to the images of snakes were shorter than RTs to the images of flowers. In addition, schoolchildren consistently responded to the presented stimuli more quickly than preschool children.
Next, we subsequently analyzed the influence of stimulus colours separately for each of age class (school or preschool children). When the collected data for schoolchildren were analyzed by a 2 (with/without ASD, PARTICIPANT) × 2 (snake/flower, IMAGE) × 3 (red/green/blue, COLOR) ANOVA (analysis of variance), all of the three main effects were statistically significant (F (1, 18) = 10.046, p = 0.005, ηG2 = 0.345 for PARTICIPANT; F (1, 18) = 11.813, p = 0.003, ηG2 = 0.00925 for IMAGE; F (2, 36) = 8.825, p = 0.001, ηG2 = 0.013 for COLOR). The interaction between PARTICIPANT and IMAGE was not significant (F (1, 18) = 0.884, p = 0.360, ηG2 = 0.000698). The interaction between PARTICIPANT and COLOR was not significant, either (F (2, 36) = 1.437, p = 0.251, ηG2 = 0.00227), and neither was that between IMAGE and COLOR (F (2, 36) = 0.772, p = 0.470, ηG2 = 0.000649). The interaction among PARTICIPANT, IMAGE and COLOR was not significant (F (2, 36) = 1.867, p = 0.169, ηG2 = 0.00157).
Likewise, when the collected data for preschool children were analyzed by ANOVA, the main effects were statistically significant for PARTICIPANT (F (1, 18) = 7.051, p = 0.016, ηG2 = 0.198), but not for IMAGE (F (1, 18) = 1.390, p = 0.254, ηG2 = 0.00184), or for COLOR (F (2, 36) = 1.955, p = 0.156, ηG2 = 0.0293). The interaction between PARTICIPANT and IMAGE was not significant (F (1, 18) = 0.668, p = 0.424, ηG2 = 0.000884). The interaction between PARTICIPANT and COLOR was not significant, either (F (2, 36) = 2.920, p = 0.067, ηG2 = 0.0431). However, the interaction between IMAGE and COLOR tended to be significant (F (2, 36) = 0.196, p = 0.053, ηG2 = 0.0120). The interaction among PARTICIPANT, IMAGE and COLOR also tended to be significant (F (2, 36) = 2.777, p = 0.076, ηG2 = 0.0105).
Overall, the schoolchildren with ASD responded to the presented stimuli more slowly than the TD schoolchildren. In both of these participant groups, RTs to the images of snakes were shorter than RTs to the images of flowers. Regarding the six different stimuli, the TD schoolchildren responded most rapidly to the image of the red snake and most slowly to the image of the blue flower, whereas the schoolchildren with ASD responded most rapidly to the image of the green snake. Among the three stimuli of the flower images, the schoolchildren with ASD also responded most rapidly to the image of the green flower. By contrast, as in the case of schoolchildren with ASD, the preschool children with ASD responded to the presented stimuli more slowly than the TD preschool children. Subsequent analyses of simple main effects (Bonferroni correction), which were performed because of the tendency toward significant interactions between IMAGE and COLOR and among PARTICIPANT, IMAGE and COLOR, revealed that the RT to flower images when they were presented in green was shorter than the RTs to the other five stimulus images in the preschool children with ASD (ps < 0.001) whereas RTs did not differ among any of the six stimuli in the TD preschool children (ps > 0.10).