The mean proportions of correct classifications for each group, stimulus set, and type of exemplar are shown in Table
2. The main analysis was a 2-between, 1-within mixed model analysis of variance (ANOVA) on the proportion of correct classifications; with group (memorize, control) and stimulus set (with feature, without feature) as between-subjects variables and type of exemplar (complete exemplar, fragment) as within-subjects variable. The ANOVA showed significant main effects of group (
F(1,52) = 40.217, MSE = 0.025,
P < 0.001) and type of exemplar (
F(1,52) = 24.916, MSE = 0.010,
P < 0.001), significant two-way interactions of group and type of exemplar (
F(1,52) = 21,921, MSE = 0.010,
P < 0.001) and of stimulus set and type of exemplar (
F(1,52) = 30.049, MSE = 0.010,
P < 0.001) and a significant three-way interaction of group, stimulus set and type of exemplar (
F(1,52) = 23.395, MSE = 0.010,
P < 0.001). Because main effects and two-way interactions are qualified by this three-way interaction, they will not be interpreted.
Table 2
Mean proportions of correct classifications and standard deviations for each type of exemplar by stimulus set and group for Experiment 1 and Experiment 2
Experiment 1 |
Memorize | 0.896 (0.148) | 0.527 (0.126) | 0.670 (0.157) | 0.682 (0.149) |
Control | 0.521 (0.174) | 0.503 (0.068) | 0.494 (0.107) | 0.500 (0.080) |
Experiment 2 |
Memorize | 0.772 (0.178) | 0.621 (0.169) | | |
Control | 0.506 (0.081) | 0.503 (0.040) | | |
The contribution of stimulus set to the three-way interaction is examined first, because participants were expected to learn different characteristics of the two sets of stimuli. For the stimulus set with a feature, there was a significant interaction between group and type of exemplar (F(1,26) = 33.905, MSE = 0.013, P < 0.001). Independent samples t tests showed that more complete exemplars were classified correctly by the memorize group than by the control group (t(26) = 6.139, P < 0.001). For fragments, however, there was no significant difference (t(26) < 1, 95% CI = −0.055 to 0.102). For the stimulus set without a feature, only the main effect of group was significant (F(1,26) = 17.137, MSE = 0.026, P < 0.001). The proportion of correct classifications was higher for the memorize group (M = 0.676, SD = 0.143) than for the control group (M = 0.497, SD = 0.075).
The ANOVA on the consistency scores showed the same pattern of results (see Table
3), indicating that the accuracy data were not biased by the way the grammars were assigned to the sides of the screen for the control group. In addition, this analysis indicated that participants who memorized exemplars containing a perfectly predictive feature did not learn any other characteristics of the grammars. If they had learned other characteristics, but failed to associate those with a side of the screen, they would have been more consistent than control participants in grouping fragments from the same grammar together. In summary, the results indicate that participants who memorized exemplars with a perfectly predictive feature were biased to learn only this characteristic, whereas participants who memorized exemplars without such a feature learned the less predictive characteristics of each grammar.
Table 3
Consistency analyses
Stimulus set × Group × Type of exemplar | F(1,52) = 19.496*** | |
Without feature |
Group | F(1,26) = 12.519** | |
With feature |
Group × Type of exemplar | F(1,26) = 19.866*** | F(1,26) = 4.417* |
Complete exemplars |
Group | t(26) = 5.315*** | t(16.0) = 5.063*** |
Fragments |
Group | t(26) = 1.604 | t(14.6) = 3.287** |