The effect of incremental changes in phonotactic probability and neighborhood density on word learning by preschool children

Abstract

Purpose: Phonotactic probability or neighborhood density has predominately been defined through the use of gross distinctions (i.e., low vs. high). In the current studies, the authors examined the influence of finer changes in probability (Experiment 1) and density (Experiment 2) on word learning.

Method: The authors examined the full range of probability or density by sampling 5 nonwords from each of 4 quartiles. Three- and 5-year-old children received training on nonword-nonobject pairs. Learning was measured in a picture-naming task immediately following training and 1 week after training. Results were analyzed through the use of multilevel modeling.

Results: A linear spline model best captured nonlinearities in phonotactic probability. Specifically, word learning improved as probability increased in the lowest quartile, worsened as probability increased in the mid-low quartile, and then remained stable and poor in the 2 highest quartiles. An ordinary linear model sufficiently described neighborhood density. Here, word learning improved as density increased across all quartiles.

Conclusion: Given these different patterns, phonotactic probability and neighborhood density appear to influence different word learning processes. Specifically, phonotactic probability may affect recognition that a sound sequence is an acceptable word in the language and is a novel word for the child, whereas neighborhood density may influence creation of a new representation in long-term memory.

Keywords: neighborhood density; phonotactic probability; spline regression; vocabulary; word learning.

Figure 1

Mean proportion correct for Experiment 1: Phonotactic Probability (top panel, z scores) and Experiment 2: Neighborhood Density (bottom panel, raw values), collapsed across time and age. Circles represent individual nonwords (Experiment 1: Phonotactic Probability) or mean proportion correct across nonwords with the same neighborhood density (Experiment 2: Neighborhood Density). Vertical grey lines indicate the dividing points between the four quartiles of the distribution: lowest, midlow, midhigh, highest. The four solid lines are the linear fit lines for each quartile (i.e., lowest, midlow, midhigh, highest). This corresponds to the fully-segmented spline model. The dashed line is the linear fit line for the full distribution. This corresponds to the linear model.