The Road to Language Learning Is Not Entirely Iconic: Iconicity, Neighborhood Density, and Frequency Facilitate Acquisition of Sign Language

Abstract

Iconic mappings between words and their meanings are far more prevalent than once estimated and seem to support children's acquisition of new words, spoken or signed. We asked whether iconicity's prevalence in sign language overshadows two other factors known to support the acquisition of spoken vocabulary: neighborhood density (the number of lexical items phonologically similar to the target) and lexical frequency. Using mixed-effects logistic regressions, we reanalyzed 58 parental reports of native-signing deaf children's productive acquisition of 332 signs in American Sign Language (ASL; Anderson & Reilly, 2002) and found that iconicity, neighborhood density, and lexical frequency independently facilitated vocabulary acquisition. Despite differences in iconicity and phonological structure between signed and spoken language, signing children, like children learning a spoken language, track statistical information about lexical items and their phonological properties and leverage this information to expand their vocabulary.

Keywords: frequency; iconicity; open data; phonological neighborhood density; sign language; vocabulary acquisition.

Fig. 1.

The signs for mommy, cookie, and milk in American Sign Language. These signs have iconicity ratings of 1.2, 3.3, and 4.2, respectively, on a 7-point scale.

Fig. 2.

Distribution of vocabulary size by age in the current sample. Vocabulary size was calculated over the 332 items used in the current analyses. The rug plot illustrates the marginal distributions of age and vocabulary size.

Fig. 3.

Comparison of the lexical properties of the CDI and non-CDI items in the ASL-LEX database. From left to right, the graphs show the distribution of signs according to their subjective frequency, iconicity, and neighborhood density. CDI = ASL Communication Development Inventories (Anderson & Reilly, 2002).

Fig. 4.

Predicted probability of a child having acquired a word given the child’s age (upper left) and the sign’s iconicity (upper right), neighborhood density (lower left), and subjective frequency (lower right). These probabilities were calculated using a link inverse function and reflect marginal effects (i.e., all other predictors in a given model were set to their mean).

Fig. 5.

Illustration of the two-way interaction between age and iconicity. Log odds (logit) of sign acquisition is shown as a function of iconicity, separately for each age quartile and the minimum and maximum ages (z-transformed values; translations into raw ages are presented to facilitate interpretation).

Fig. 6.

Results of the Monte Carlo analysis. The circles show the observed individual-level means for iconicity, frequency, and neighborhood density as a function of the child’s vocabulary size. The vertical lines indicate the 95th percentile of the randomly generated vocabulary for each child. Nontransformed values for frequency and iconicity are plotted for interpretability; the results were similar for the transformed and nontransformed measures.