Can Chunk Size Differences Explain Developmental Changes in Lexical Learning?

Abstract

In three experiments, we investigated Hebb repetition learning (HRL) differences between children and adults, as a function of the type of item (lexical vs. sub-lexical) and the level of item-overlap between sequences. In a first experiment, it was shown that when non-repeating and repeating (Hebb) sequences of words were all permutations of the same words, HRL was slower than when the sequences shared no words. This item-overlap effect was observed in both children and adults. In a second experiment, we used syllable sequences and we observed reduced HRL due to item-overlap only in children. The findings are explained within a chunking account of the HRL effect on the basis of which we hypothesize that children, compared with adults, chunk syllable sequences in smaller units. By hypothesis, small chunks are more prone to interference from anagram representations included in the filler sequences, potentially explaining the item-overlap effect in children. This hypothesis was tested in a third experiment with adults where we experimentally manipulated the chunk size by embedding pauses in the syllable sequences. Interestingly, we showed that imposing a small chunk size caused adults to show the same behavioral effects as those observed in children. Departing from the analogy between verbal HRL and lexical development, the results are discussed in light of the less-is-more hypothesis of age-related differences in language acquisition.

Keywords: Hebb repetition learning; chunking; language acquisition; lexical development; working memory.

Figure 1

An example of a within-block overlap manipulation. Two different Hebb sequences are presented within one learning block. The overlapping Hebb sequence contains the same items as the intervening filler sequences. The non-overlapping Hebb sequence contains different items. Only the first 10 trials are shown.

Figure 2

Performance (percentage of correct scores) as a function of Sequence type (filler vs. Hebb non-overlap vs. Hebb overlap) and Sequence repetition (1–8) in both children and adults, Experiment 1. Left panel: performance for adults. Right panel: performance for children.

Figure 3

Mean percentage of items correctly recalled (with standard errors) for Hebb and filler sequences by sequence Halves, Experiment 1.

Figure 4

Performance (percentage of correct scores) as a function of Sequence type (filler vs. Hebb non-overlap vs. Hebb overlap) and Sequence repetition (1–8) in both children and adults, Experiment 2. Left panel: performance for adults. Right panel: performance for children.

Figure 5

Mean percentage of items correctly recalled (with standard errors) for Hebb and filler sequences by sequence Halves, in both children and adults, Experiment 2. Left panel: performance for adults. Right panel: performance for children.

Figure 6

Performance (percentage of correct scores) as a function of Sequence type (filler vs. Hebb non-overlap vs. Hebb overlap) and Sequence repetition (1–8) in the group with chunking and the control group, Experiment 3. Left panel: performance for control adults. Right panel: performance for chunk-encouraged adults.

Figure 7

Mean percentage of items correctly recalled (with standard errors) for Hebb and filler sequences by sequence Halves, in both control and chunk adults, Experiment 3. Left panel: performance for control adults. Right panel: performance for chunk adults.