The Interaction of Phonology and Morphosyntax in Early Language Development: A Study of English-Acquiring Toddlers

Abstract

The development of grammatical morphology in early childhood is often treated independently of phonological development, yet toddlers' ability to produce and comprehend morphosyntactic forms may be constrained by phonological factors. We examined 24 English-acquiring children (mean age 24 months) using comprehension tasks and spontaneous speech samples collected every two weeks over a six-month period. Phonotactic complexity significantly predicted comprehension of third-person singular and plural forms. Analysis of speech samples revealed that children preferentially produced verbs and nouns with simpler word-final phonotactics, suggesting a phonological constraint on early morphosyntactic output. Results indicate that the emergence of grammatical morphology is shaped not by abstract grammatical principles alone, but by interaction with phonological processing capacities.

Introduction

The acquisition of grammatical morphology in English is a protracted process, with productive use of tense and agreement markers typically emerging between 24 and 36 months of age (Brown, 1973). Traditional accounts have emphasised the role of innate grammatical knowledge and input frequency, treating morphosyntactic acquisition as a process largely independent of other linguistic domains. However, recent work in developmental phonology and psycholinguistics raises the possibility that the phonological structure of morphemes, and the phonotactic complexity they create in word-final position, may constrain toddlers' capacity to perceive, store, and produce morphological forms.

The third-person singular marker "-s" (as in "walks" or "talks") and the plural marker "-s" are amongst the earliest grammatical morphemes to appear in English. Yet acquisition of productive marking of tense and number is frequently delayed relative to the emergence of these forms in comprehension. We hypothesised that phonological factors—specifically the relationship between verb or noun phonotactics and the phonotactic requirements imposed by the suffix—would significantly predict individual differences in morphological comprehension and production.

Method

Participants

Twenty-four monolingual English-acquiring children (mean age 24.3 months, SD = 2.1; 12 female) were recruited from middle-class families in the Greater Toronto Area. Parents reported normal language exposure and no family history of language disorder.

Procedure

Comprehension was assessed using a preferential looking procedure adapted from Naigles (1990). On each trial, two video scenes appeared side-by-side: one depicting a singular referent (e.g., a ball rolling) and another depicting a plural action (e.g., balls rolling). While children viewed the scenes, an audio sentence was played (e.g., "Look! The ball rolls" or "Look! The balls roll"). We measured the proportion of time children looked toward the correct referent. The stimuli included 24 test sentences: 12 with third-person singular forms and 12 with plural forms. Phonotactic complexity of the verb or noun base (prior to the suffix) was quantified using a corpus-derived measure: the proportion of English words sharing the word-final consonant cluster of the test stimulus. For example, a word ending in "-ft" (as in "lift") was rated as high-complexity because few English words share this cluster; a word ending in "-p" was rated low-complexity.

Spontaneous speech samples were collected biweekly during 20-minute play sessions with the experimenter. Sessions were audio-recorded, transcribed, and coded for all verb and noun productions. For each target morpheme produced, the phonotactic complexity of the base was computed.

Results

A one-way ANOVA revealed that comprehension accuracy was significantly higher for plural and singular forms attached to low-complexity phonotactic bases (M = 78.2%, SD = 8.1%) than to high-complexity bases (M = 62.3%, SD = 11.7%), F(1, 46) = 18.6, p < .001. Phonotactic complexity also predicted production: across the six-month period, children were significantly more likely to produce novel morphologically-marked forms (e.g., overgeneralising the plural to novel nouns, as in "mouses") with simple phonotactic bases, *χ²(1, N = 247) = 12.4, p < .001. A Pearson correlation across participants confirmed that individual comprehension accuracy was positively correlated with the proportion of low-complexity verbs and nouns in each child's spontaneous speech sample, r(24) = .51, p < .01.

Discussion

These findings indicate that the emergence of English grammatical morphology is constrained by phonological factors. The systematic advantage for morphemes attached to phonotactically simpler bases suggests that toddlers' capacity to perceive and process morphologically-marked words is modulated by the phonotactic well-formedness of the resulting form. This aligns with recent connectionist models of language development (Plunkett & Marchman, 1993) which propose that learning is sensitive to phonological structure, and extends those models to the domain of morphosyntactic development.

The preferential production of marked forms with simple phonotactics suggests that children may rely on implicit phonological templates when generating novel morphological forms. This has important implications for understanding individual differences in grammatical development and for explaining why certain morphemes (such as the present progressive "-ing," which is phonotactically less demanding) are acquired earlier than others. Future work should examine whether similar phonological constraints shape the acquisition of morphology in languages with different phonotactic systems.

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