Excerpts from Shultz, T. R., & Cohen, L. B. (2004). Modeling age differences in infant category learning. Infancy, 5(2), 153-171.
(Readers are advised to consult the published article for
full details.)
“Infants are well known to decrease their attention to repeated stimuli and to recover their attention to novel stimuli, but not to familiar stimuli. Recovery of attention to a novel test stimulus suggests its novelty; little or no recovery indicates familiarity. When applied to infant category learning, this pattern of decrease and selective recovery of attention presumably signals the gradual construction of a conceptual structure for a category of stimuli and the discrimination of novel stimuli fitting that category from novel stimuli not fitting the category. Infants are assumed to construct representational categories for repeated stimuli, ignoring novel stimuli that are consistent with the category, while concentrating on those novel stimuli that are not members of the category. See Cohen and Younger (1983) or Younger and Cohen (1985) for reviews of this literature.
There is also evidence that the use of correlated features in category formation becomes increasingly important with development. After repeated presentation of visual stimuli with correlated features, young infants recover attention to stimuli with novel features more than to stimuli with either correlated or uncorrelated familiar features (Younger and Cohen, 1983, 1986). In contrast, older infants recover attention to both stimuli with novel features and familiar uncorrelated features more than to stimuli with familiar correlated features. This pattern of recovery of attention suggests that young infants have learned about the individual stimulus features, but not about the relationship among features, whereas older infants have also learned about how these features are correlated with one another.”
Younger and Cohen (1986, Experiment 2):
“… We focus first on the most important finding, the interaction between age and preference for correlated and uncorrelated test stimuli. We then cover additional, related findings on discrimination of a correlated test stimulus and preference for novel feature values.
[In the Younger and Cohen Experiment 2 (1986), there were four familiarization stimuli that were repeatedly presented to the infants.] … The stimuli were line drawings of imaginary animals, characterized by three features with three values each. The body could be that of a giraffe, cow, or elephant. The tail could be feathered, fluffy, or a horse’s tail. And the feet could be webbed, hoofed, or club feet. Two sets of stimuli were used. In each set, features A and B were perfectly correlated across stimuli. Feature C was uncorrelated with features A and B.
The participants were 24 infants at each of three ages: 4, 7, and 10 months. Each infant received twelve, 20-second familiarization trials to one of the two sets of animals, each being presented three times.
Following the familiarization procedure each infant received 20-second presentations of each of the three test stimuli… The correlated test stimulus preserved both the feature values and t correlation pattern of the familiarization stimuli. The uncorrelated test stimulus used the same feature values but broke the pattern of correlation between features A and B. Finally, the novel test stimulus employed novel feature values.
Mean fixation times per trail to the three test stimuli by 4- and 10-month-old infants are presented in Figure 1 [not shown]. As noted, the 4-month-olds recovered attention more to the novel stimulus than to the correlated and uncorrelated stimuli, whereas 10-month-olds recovered attention more to the uncorrelated and novel stimuli than to the correlated stimulus. Thus, 4-month-olds seem to have learned only about the feature values, whereas 10-month-olds also learned about the pattern of correlations between features during the familiarization procedure. Curiously, 7-month-olds failed to habituate their attention during the familiarization phrase, so their recovery data are not easily interpretable. It is as if they failed to learn anything about the stimuli.
Younger and Cohen (1986, Experiment 3) and Cohen and Arthur (unpublished).
“… Experiment 3 (Younger & Cohen, 1986) tested two different explanations of the interaction between age and test stimulus: increasing sensitivity to correlations versus similarity between habituation and test stimuli. In Experiment 2, the correlated test item was most similar to those in the familiarization set (indeed it was identical to stimulus 4), followed by the uncorrelated test item, and then the novel test item. It is thus possible that age differences in recovery reflect a lower novelty threshold for older infants than for younger infant. Older infants may have responded more to the uncorrelated and novel test items because these stimuli were less similar to the familiarizations items than was the correlated test stimulus. Younger infants, in contrast, may have responded to both correlated and uncorrelated items as familiar because neither item reached its novelty threshold. On the other hand, it might have been as previously stated, that the older infants were sensitive to correlation information, and the younger infants were not.
These two explanations were tested in Experiment 3 by removing the correlated test item from the familiarization set. This ensured that the uncorrelated test item was now most similar to the familiarization set, followed by the correlated test item, and finally by the novel test item.
Eighteen infants were tested at each of two ages: 7 and 10 months, 9 infants per condition. Each infant received nine 20-second familiarization trials in which each stimulus was presented three times. Following the familiarization phrase, each test stimulus was present once for 20 seconds.
Again the 7-month-olds failed to habituate, thus rendering their recovery data difficult to interpret. The 10-month-olds showed the same recovery pattern as in Experiment 2, as shown in Figure 2 [not shown]. If recovery was based on similarity, they should have recovered attention more to the correlated test item than to uncorrelated test item. But if recovery was based on sensitivity to correlations, they should have recovered attention more to the uncorrelated test item than to the correlated test item, which they in fact did. We recently ran 12 4-month-olds on essentially the same task as Experiment 3 (Cohen & Arthur, unpublished). The 4-month-olds’ data are also presented in Figure 2 for comparison … Four-month-olds once again produced the pattern characteristic of responding to independent features rather than the correlation among features. We take the interaction between age and test stimulus shown in both Figures 1 and 2 to be the main results to cover in a computer simulation.”