The Independent Effects of Phonotactic Probability and Neighborhood Density on Lexical Acquisition by Preschool Children.

The goal of this research was to disentangle effects of phonotactic probability, the likelihood of occurrence of a sound sequence, and neighborhood density, the number of phonologically similar words, in lexical acquisition. Two word learning experiments were conducted with 4-year-old children. Experiment 1 manipulated phonotactic probability while holding neighborhood density and referent characteristics constant. Experiment 2 manipulated neighborhood density while holding phonotactic probability and referent characteristics constant. Learning was tested at two time points (immediate vs. retention) in both a naming and referent identification task, although only data from the referent identification task were analyzed due to poor performance in the naming task. Results showed that children were more accurate learning rare sound sequences than common sound sequences and this was consistent across time points. In contrast, the effect of neighborhood density varied by time. Children were more accurate learning sparse sound sequences than dense sound sequences at the immediate test point but accuracy for dense sound sequences significantly improved by the retention test without further training. It was hypothesized that phonotactic probability and neighborhood density influenced different cognitive processes that underlie lexical acquisition.