Lexical Predictors of Intelligibility in Young Children's Speech

Abstract

Purpose: Speech perception is a probabilistic process, integrating bottom-up and top-down sources of information, and the frequency and phonological neighborhood of a word can predict how well it is perceived. In addition to asking how intelligible speakers are, it is important to ask how intelligible individual words are. We examined whether lexical features of words influenced intelligibility in young children. In particular, we applied the neighborhood activation model, which posits that a word's frequency and the overall frequency of a word's phonological competitors jointly affect the intelligibility of a word.

Method: We measured the intelligibility of 165 children between 30 and 47 months in age on 38 different single words. We performed an item response analysis using generalized mixed-effects logistic regression, adding word-level characteristics (target frequency, neighborhood competition, motor complexity, and phonotactic probability) as predictors of intelligibility.

Results: There was considerable variation among the words and the children, but between-word variability was larger in magnitude than between-child variability. There was a clear positive effect of target word frequency and a negative effect of neighborhood competition. We did not find a clear negative effect of motor complexity, and phonotactic probability did not have any effect on intelligibility.

Conclusion: Word frequency and neighborhood competition both had an effect on intelligibility in young children's speech, so listener expectations are an important factor in the selection of items for children's intelligibility assessment.

Figure 1.

Word variability is greater than child variability. Box plots compare child-level average intelligibilities (across words) and word-level average intelligibility (across children). Children were split into 6-month age bins, and the box plots are labeled with the age range and the number of children in the age bin. The wider box plots for words indicate greater variability among words than children. We had the model simulate intelligibility expectations for a 3-year-old child on a word with average target frequency and average neighborhood competition. In one simulation, we simulated new words for a typical child to show item variation, and in another, we simulated new children for a typical item to show child variation.

Figure 2.

Effects of target word frequency and neighborhood competition on expected intelligibility. There is a clear positive effect of frequency on intelligibility, and there is a likely negative effect on neighbor competition. Model predictions are for an average item with a complexity of 10 for an average 3-year-old child. Points represent the observed mean for each item across all children. For the purposes of illustration, the words were split into three bins based on neighborhood competition in the bottom row. The model predictions in each bin used are based on the median neighborhood competition value in each bin. That the frequency slope increases with neighborhood competition suggests an interaction between the two.